| 1. |
- van de Werken, Harmen, et al.
(författare)
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Hydrogenomics of the extremely thermophilic bacterium Caldicellulosiruptor saccharolyticus
- 2008
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Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 74:21, s. 6720-6729
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Tidskriftsartikel (refereegranskat)abstract
- Caldicellulosiruptor saccharolyticus is an extremely thermophilic, gram-positive anaerobe which ferments cellulose-, hemicellulose- and pectin-containing biomass to acetate, CO2, and hydrogen. Its broad substrate range, high hydrogen-producing capacity, and ability to coutilize glucose and xylose make this bacterium an attractive candidate for microbial bioenergy production. Here, the complete genome sequence of C. saccharolyticus, consisting of a 2,970,275-bp circular chromosome encoding 2,679 predicted proteins, is described. Analysis of the genome revealed that C. saccharolyticus has an extensive polysaccharide-hydrolyzing capacity for cellulose, hemicellulose, pectin, and starch, coupled to a large number of ABC transporters for monomeric and oligomeric sugar uptake. The components of the Embden-Meyerhof and nonoxidative pentose phosphate pathways are all present; however, there is no evidence that an Entner-Doudoroff pathway is present. Catabolic pathways for a range of sugars, including rhamnose, fucose, arabinose, glucuronate, fructose, and galactose, were identified. These pathways lead to the production of NADH and reduced ferredoxin. NADH and reduced ferredoxin are subsequently used by two distinct hydrogenases to generate hydrogen. Whole-genome transcriptome analysis revealed that there is significant upregulation of the glycolytic pathway and an ABC-type sugar transporter during growth on glucose and xylose, indicating that C. saccharolyticus coferments these sugars unimpeded by glucose-based catabolite repression. The capacity to simultaneously process and utilize a range of carbohydrates associated with biomass feedstocks is a highly desirable feature of this lignocelluloseutilizing, biofuel-producing bacterium.
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| 2. |
- Bhattacharya, Abhishek, et al.
(författare)
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Cross-Feeding and Enzymatic Catabolism for Mannan-Oligosaccharide Utilization by the Butyrate-Producing Gut Bacterium Roseburia hominis A2-183
- 2022
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Ingår i: Microorganisms. - : MDPI AG. - 2076-2607. ; 10:12
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Tidskriftsartikel (refereegranskat)abstract
- β-Mannan is abundant in the human diet and in hemicellulose derived from softwood. Linear or galactose-substituted β-mannan-oligosaccharides (MOS/GMOSs) derived from β-mannan are considered emerging prebiotics that could stimulate health-associated gut microbiota. However, the underlying mechanisms are not yet resolved. Therefore, this study investigated the cross-feeding and metabolic interactions between Bifidobacterium adolescentis ATCC 15703, an acetate producer, and Roseburia hominis A2-183 DSMZ 16839, a butyrate producer, during utilization of MOS/GMOSs. Cocultivation studies suggest that both strains coexist due to differential MOS/GMOS utilization, along with the cross-feeding of acetate from B. adolescentis E194a to R. hominis A2-183. The data suggest that R. hominis A2-183 efficiently utilizes MOS/GMOS in mono- and cocultivation. Notably, we observed the transcriptional upregulation of certain genes within a dedicated MOS/GMOS utilization locus (RhMosUL), and an exo-oligomannosidase (RhMan113A) gene located distally in the R. hominis A2-183 genome. Significantly, biochemical analysis of β-1,4 mannan-oligosaccharide phosphorylase (RhMOP130A), α-galactosidase (RhGal36A), and exo-oligomannosidase (RhMan113A) suggested their potential synergistic role in the initial utilization of MOS/GMOSs. Thus, our results enhance the understanding of MOS/GMOS utilization by potential health-promoting human gut microbiota and highlight the role of cross-feeding and metabolic interactions between two secondary mannan degraders inhabiting the same ecological niche in the gut.
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| 3. |
- Bielen, Abraham A. M., et al.
(författare)
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Pyrophosphate as a central energy carrier in the hydrogen-producing extremely thermophilic Caldicellulosiruptor saccharolyticus
- 2010
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Ingår i: FEMS Microbiology Letters. - : Oxford University Press (OUP). - 1574-6968 .- 0378-1097. ; 307:1, s. 48-54
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Tidskriftsartikel (refereegranskat)abstract
- The role of inorganic pyrophosphate (PPi) as an energy carrier in the central metabolism of the extremely thermophilic bacterium Caldicellulosiruptor saccharolyticus was investigated. In agreement with its annotated genome sequence, cell extracts were shown to exhibit PPi-dependent phosphofructokinase and pyruvate phosphate dikinase activity. In addition, membrane-bound pyrophosphatase activity was demonstrated, while no significant cytosolic pyrophosphatase activity was detected. During the exponential growth phase, high PPi levels (approximately 4 +/- 2 mM) and relatively low ATP levels (0.43 +/- 0.07 mM) were found, and the PPi/ATP ratio decreased 13-fold when the cells entered the stationary phase. Pyruvate kinase activity appeared to be allosterically affected by PPi. Altogether, these findings suggest an important role for PPi in the central energy metabolism of C. saccharolyticus.
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| 4. |
- Bergdahl, Basti, et al.
(författare)
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Dynamic metabolomics differentiates between carbon and energy starvation in recombinant Saccharomyces cerevisiae fermenting xylose
- 2012
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Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 5:34
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Tidskriftsartikel (refereegranskat)abstract
- Background: The concerted effects of changes in gene expression due to changes in the environment are ultimately reflected in the metabolome. Dynamics of metabolite concentrations under a certain condition can therefore give a description of the cellular state with a high degree of functional information. We used this potential to evaluate the metabolic status of two recombinant strains of Saccharomyces cerevisiae during anaerobic batch fermentation of a glucose/xylose mixture. Two isogenic strains were studied, differing only in the pathways used for xylose assimilation: the oxidoreductive pathway with xylose reductase (XR) and xylitol dehydrogenase (XDH) or the isomerization pathway with xylose isomerase (XI). The isogenic relationship between the two strains ascertains that the observed responses are a result of the particular xylose pathway and not due to unknown changes in regulatory systems. An increased understanding of the physiological state of these strains is important for further development of efficient pentose-utilizing strains for bioethanol production. Results: Using LC-MS/MS we determined the dynamics in the concentrations of intracellular metabolites in central carbon metabolism, nine amino acids, the purine nucleotides and redox cofactors. The general response to the transition from glucose to xylose was increased concentrations of amino acids and TCA-cycle intermediates, and decreased concentrations of sugar phosphates and redox cofactors. The two strains investigated had significantly different uptake rates of xylose which led to an enhanced response in the XI-strain. Despite the difference in xylose uptake rate, the adenylate energy charge remained high and stable around 0.8 in both strains. In contrast to the adenylate pool, large changes were observed in the guanylate pool. Conclusions: The low uptake of xylose by the XI-strain led to several distinguished responses: depletion of key metabolites in glycolysis and NADPH, a reduced GTP/GDP ratio and accumulation of PEP and aromatic amino acids. These changes are strong indicators of carbon starvation. The XR/XDH-strain displayed few such traits. The coexistence of these traits and a stable adenylate charge indicates that xylose supplies energy to the cells but does not suppress a response similar to carbon starvation. Particular signals may play a role in the latter, of which the GTP/GMP ratio could be a candidate as it decreased significantly in both strains.
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| 5. |
- Bergdahl, Basti, et al.
(författare)
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Engineering yeast hexokinase 2 for improved tolerance toward xylose-induced inactivation.
- 2013
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:9
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Tidskriftsartikel (refereegranskat)abstract
- Hexokinase 2 (Hxk2p) from Saccharomyces cerevisiae is a bi-functional enzyme being both a catalyst and an important regulator in the glucose repression signal. In the presence of xylose Hxk2p is irreversibly inactivated through an autophosphorylation mechanism, affecting all functions. Consequently, the regulation of genes involved in sugar transport and fermentative metabolism is impaired. The aim of the study was to obtain new Hxk2p-variants, immune to the autophosphorylation, which potentially can restore the repressive capability closer to its nominal level. In this study we constructed the first condensed, rationally designed combinatorial library targeting the active-site in Hxk2p. We combined protein engineering and genetic engineering for efficient screening and identified a variant with Phe159 changed to tyrosine. This variant had 64% higher catalytic activity in the presence of xylose compared to the wild-type and is expected to be a key component for increasing the productivity of recombinant xylose-fermenting strains for bioethanol production from lignocellulosic feedstocks.
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| 6. |
- Bergdahl, Basti, et al.
(författare)
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Physiological effects of over-expressing compartment-specific components of the protein folding machinery in xylose-fermenting Saccharomyces cerevisiae
- 2014
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Ingår i: BMC Biotechnology. - : Springer Science and Business Media LLC. - 1472-6750. ; 14:28
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Tidskriftsartikel (refereegranskat)abstract
- Background: Efficient utilization of both glucose and xylose is necessary for a competitive ethanol production from lignocellulosic materials. Although many advances have been made in the development of xylose-fermenting strains of Saccharomyces cerevisiae, the productivity remains much lower compared to glucose. Previous transcriptional analyses of recombinant xylose-fermenting strains have mainly focused on central carbon metabolism. Very little attention has been given to other fundamental cellular processes such as the folding of proteins. Analysis of previously measured transcript levels in a recombinant XR/XDH-strain showed a wide down-regulation of genes targeted by the unfolded protein response during xylose fermentation. Under anaerobic conditions the folding of proteins is directly connected with fumarate metabolism and requires two essential enzymes: FADH2-dependent fumarate reductase (FR) and Ero1p. In this study we tested whether these enzymes impair the protein folding process causing the very slow growth of recombinant yeast strains on xylose under anaerobic conditions. Results: Four strains over-expressing the cytosolic (FRD1) or mitochondrial (OSM1) FR genes and ERO1 in different combinations were constructed. The growth and fermentation performance was evaluated in defined medium as well as in a complex medium containing glucose and xylose. Over-expression of FRD1, alone or in combination with ERO1, did not have any significant effect on xylose fermentation in any medium used. Over-expression of OSM1, on the other hand, led to a diversion of carbon from glycerol to acetate and a decrease in growth rate by 39% in defined medium and by 25% in complex medium. Combined over-expression of OSM1 and ERO1 led to the same diversion of carbon from glycerol to acetate and had a stronger detrimental effect on the growth in complex medium. Conclusions: Increasing the activities of the FR enzymes and Ero1p is not sufficient to increase the anaerobic growth on xylose. So additional components of the protein folding mechanism that were identified in transcription analysis of UPR related genes may also be limiting. This includes i) the transcription factor encoded by HAC1 ii) the activity of Pdi1p and iii) the requirement of free FAD during anaerobic growth.
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| 7. |
- Björkmalm, Johanna, et al.
(författare)
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A non-linear model of hydrogen production by Caldicellulosiruptor saccharolyticus for diauxic-like consumption of lignocellulosic sugar mixtures
- 2018
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Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 11:1, s. 1-15
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Tidskriftsartikel (refereegranskat)abstract
- Background: Caldicellulosiruptor saccharolyticus is an attractive hydrogen producer suitable for growth on various lignocellulosic substrates. The aim of this study was to quantify uptake of pentose and hexose monosaccharides in anindustrial substrate and to present a kinetic growth model of C. saccharolyticus that includes sugar uptake on defined and industrial media. The model is based on Monod and Hill kinetics extended with gas-to-liquid mass transfer and acybernetic approach to describe diauxic-like growth.Results: Mathematical expressions were developed to describe hydrogen production by C. saccharolyticus consuming glucose, xylose, and arabinose. The model parameters were calibrated against batch fermentation data. Theexperimental data included four different cases: glucose, xylose, sugar mixture, and wheat straw hydrolysate (WSH) fermentations. The fermentations were performed without yeast extract. The substrate uptake rate of C. saccharolyticuson single sugar-defined media was higher on glucose compared to xylose. In contrast, in the defined sugar mixture and WSH, the pentoses were consumed faster than glucose. Subsequently, the cultures entered a lag phasewhen all pentoses were consumed after which glucose uptake rate increased. This phenomenon suggested a diauxic-like behavior as was deduced from the successive appearance of two peaks in the hydrogen and carbon dioxideproductivity. The observation could be described with a modified diauxic model including a second enzyme system with a higher affinity for glucose being expressed when pentose saccharides are consumed. This behavior was morepronounced when WSH was used as substrate.Conclusions: The previously observed co-consumption of glucose and pentoses with a preference for the latter was herein confirmed. However, once all pentoses were consumed, C. saccharolyticus most probably expressed anotheruptake system to account for the observed increased glucose uptake rate. This phenomenon could be quantitatively captured in a kinetic model of the entire diauxic-like growth process. Moreover, the observation indicates a regulationsystem that has fundamental research relevance, since pentose and glucose uptake in C. saccharolyticus has only been described with ABC transporters, whereas previously reported diauxic growth phenomena have been correlatedmainly to PTS systems for sugar uptake.
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| 8. |
- Boshagh, Fatemeh, et al.
(författare)
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Application of kinetic models in dark fermentative hydrogen production–A critical review
- 2022
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Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 0360-3199. ; 47:52, s. 21952-21968
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Forskningsöversikt (refereegranskat)abstract
- Kinetic modeling could be viewed as an important step in developing a bioprocess, since models can be used in process control, reducing costs and optimizing processes. In the present study, the application of kinetic models in dark fermentative hydrogen production has been investigated. A wide variety of kinetic models are addressed and compared regarding their accuracy to fit the data. This literature survey indicates that the modified Gompertz was extensively used to describe the production of hydrogen, organic acids and alcohols, substrate degradation, and biomass growth. The development of kinetic models can assist researchers to identify the most important variables, facilitate future research, and maximize hydrogen production.
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| 9. |
- Byrne, Eoin, et al.
(författare)
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Characterization and adaptation of Caldicellulosiruptor strains to higher sugar concentrations, targeting enhanced hydrogen production from lignocellulosic hydrolysates
- 2021
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Ingår i: Biotechnology for Biofuels. - : BioMed Central Ltd. - 1754-6834. ; 14:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: The members of the genus Caldicellulosiruptor have the potential for future integration into a biorefinery system due to their capacity to generate hydrogen close to the theoretical limit of 4 mol H2/mol hexose, use a wide range of sugars and can grow on numerous lignocellulose hydrolysates. However, members of this genus are unable to survive in high sugar concentrations, limiting their ability to grow on more concentrated hydrolysates, thus impeding their industrial applicability. In this study five members of this genus, C.owensensis, C. kronotskyensis, C.bescii, C.acetigenus and C.kristjanssonii, were developed to tolerate higher sugar concentrations through an adaptive laboratory evolution (ALE) process. The developed mixed population C.owensensis CO80 was further studied and accompanied by the development of a kinetic model based on Monod kinetics to quantitatively compare it with the parental strain. Results: Mixed populations of Caldicellulosiruptor tolerant to higher glucose concentrations were obtained with C.owensensis adapted to grow up to 80 g/L glucose; other strains in particular C. kristjanssonii demonstrated a greater restriction to adaptation. The C.owensensis CO80 mixed population was further studied and demonstrated the ability to grow in glucose concentrations up to 80 g/L glucose, but with reduced volumetric hydrogen productivities (QH2) and incomplete sugar conversion at elevated glucose concentrations. In addition, the carbon yield decreased with elevated concentrations of glucose. The ability of the mixed population C.owensensis CO80 to grow in high glucose concentrations was further described with a kinetic growth model, which revealed that the critical sugar concentration of the cells increased fourfold when cultivated at higher concentrations. When co-cultured with the adapted C.saccharolyticus G5 mixed culture at a hydraulic retention time (HRT) of 20 h, C.owensensis constituted only 0.09–1.58% of the population in suspension. Conclusions: The adaptation of members of the Caldicellulosiruptor genus to higher sugar concentrations established that the ability to develop improved strains via ALE is species dependent, with C.owensensis adapted to grow on 80 g/L, whereas C.kristjanssonii could only be adapted to 30 g/L glucose. Although C.owensensis CO80 was adapted to a higher sugar concentration, this mixed population demonstrated reduced QH2 with elevated glucose concentrations. This would indicate that while ALE permits adaptation to elevated sugar concentrations, this approach does not result in improved fermentation performances at these higher sugar concentrations. Moreover, the observation that planktonic mixed culture of CO80 was outcompeted by an adapted C.saccharolyticus, when co-cultivated in continuous mode, indicates that the robustness of CO80 mixed culture should be improved for industrial application. © 2021, The Author(s).
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| 10. |
- Byrne, Eoin, et al.
(författare)
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Reduced use of phosphorus and water in sequential dark fermentation and anaerobic digestion of wheat straw and the application of ensiled steam-pretreated lucerne as a macronutrient provider in anaerobic digestion
- 2018
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Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 11:1
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Tidskriftsartikel (refereegranskat)abstract
- Background: Current EU directives demand increased use of renewable fuels in the transportation sector but restrict governmental support for production of biofuels produced from crops. The use of intercropped lucerne and wheat may comply with the directives. In the current study, the combination of ensiled lucerne (Medicago sativa L.) and wheat straw as substrate for hydrogen and methane production was investigated. Steam-pretreated and enzymatically hydrolysed wheat straw [WSH, 76% of total chemical oxygen demand (COD)] and ensiled lucerne (LH, 24% of total COD) were used for sequential hydrogen production through dark fermentation and methane production through anaerobic digestion and directly for anaerobic digestion. Synthetic co-cultures of extreme thermophilic Caldicellulosiruptor species adapted to elevated osmolalities were used for dark fermentation. Results: Based on 6 tested steam pretreatment conditions, 5 min at 200 °C was chosen for the ensiled lucerne. The same conditions as applied for wheat straw (10 min at 200 °C with 1% acetic acid) would give similar sugar yields. Volumetric hydrogen productivities of 6.7 and 4.3 mmol/L/h and hydrogen yields of 1.9 and 1.8 mol/mol hexose were observed using WSH and the combination of WSH and LH, respectively, which were relatively low compared to those of the wild-type strains. The combinations of WSH plus LH and the effluent from dark fermentation of WSH plus LH were efficiently converted to methane in anaerobic digestion with COD removal of 85-89% at organic loading rates of COD 5.4 and 8.5 g/L/day, respectively, in UASB reactors. The nutrients in the combined hydrolysates could support this conversion. Conclusions: This study demonstrates the possibility of reducing the water addition to WSH by 26% and the phosphorus addition by 80% in dark fermentation with Caldicellulosiruptor species, compared to previous reports. WSH and combined WSH and LH were well tolerated by osmotolerant co-cultures. The yield was not significantly different when using defined media or hydrolysates with the same concentrations of sugars. However, the sugar concentration was negatively correlated with the hydrogen yield when comparing the results to previous reports. Hydrolysates and effluents from dark fermentation can be efficiently converted to methane. Lucerne can serve as macronutrient provider in anaerobic digestion. Intercropping with wheat is promising.
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| 11. |
- Cao, Rong, et al.
(författare)
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Inhibition kinetics of catabolic dehydrogenases by elevated moieties of ATP and ADP - implication for a new regulation mechanism in Lactococcus lactis
- 2010
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Ingår i: The FEBS Journal. - : Wiley. - 1742-464X. ; 277:8, s. 1843-1852
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Tidskriftsartikel (refereegranskat)abstract
- ATP and ADP inhibit, in varying degrees, several dehydrogenases of the central carbon metabolism of Lactococcus lactis ATCC 19435 in vitro, i.e. glyceraldehyde-3-phosphate dehydrogenase (GAPDH), lactate dehydrogenase (LDH) and alcohol dehydrogenase (ADH). Here we demonstrate mixed inhibition for GAPDH and competitive inhibition for LDH and ADH by adenine nucleotides in single inhibition studies. The nonlinear negative co-operativity was best modelled with Hill-type kinetics, showing greater flexibility than the usual parabolic inhibition equation. Because these natural inhibitors are present simultaneously in the cytoplasm, multiple inhibition kinetics was determined for each dehydrogenase. For ADH and LDH, the inhibitor combinations ATP plus NAD and ADP plus NAD are indifferent to each other. Model discrimination suggested that the weak allosteric inhibition of GAPDH had no relevance when multiple inhibitors are present. Interestingly, with ADH and GAPDH the combination of ATP and ADP exhibits lower dissociation constants than with either inhibitor alone. Moreover, the concerted inhibition of ADH and GAPDH, but not of LDH, shows synergy between the two nucleotides. Similar kinetics, but without synergies, were found for horse liver and yeast ADHs, indicating that dehydrogenases can be modulated by these nucleotides in a nonlinear manner in many organisms. The action of an elevated pool of ATP and ADP may effectively inactivate lactococcal ADH, but not GAPDH and LDH, providing leverage for the observed metabolic shift to homolactic acid formation in lactococcal resting cells on maltose. Therefore, we interpret these results as a regulation mechanism contributing to readjusting the flux of ATP production in L. lactis.
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| 12. |
- Carlquist, Magnus, et al.
(författare)
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Kinetic resolution of racemic 5,6-epoxy-bicyclo[2.2.1]heptane-2-one using genetically engineered Saccharomyces cerevisiae
- 2009
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Ingår i: Journal of Molecular Catalysis B: Enzymatic. - : Elsevier BV. - 1873-3158 .- 1381-1177. ; 58:2, s. 98-102
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Tidskriftsartikel (refereegranskat)abstract
- (+)-5,6-Epoxy-bicyclo[2.2.1]heptane-2-one, (+)-1, and endo-(−)-5,6-epoxy-bicyclo[2.2.1]heptane-2-ol, endo-(−)-2, were obtained by kinetic resolution of rac-1 by asymmetric bioreduction catalyzed by whole cells of a genetically engineered Saccharomyces cerevisiae yeast strain. The strain, TMB4100, had 1% phosphoglucose isomerase (PGI) activity and overexpressed a specific short-chain dehydrogenase, encoded by the gene YMR226c. The whole cell biocatalystwas demonstrated to be significantly inactivated within 24 h, thus restricting the reaction to lowconcentration. Despite this, the resolution method could be used to produce optically pure (+)-1 and endo-(−)-2 from the racemic mixture at 5 g/L substrate. At optimal conditions, 1 g of rac-1 was kinetically resolved to give (+)-1 in 95% ee and 28% yield and endo-(−)-2 in 74% ee, 80% de and 45% yield.
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| 13. |
- Ciranna, Alessandro, et al.
(författare)
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Assessment of metabolic flux distribution in the thermophilic hydrogen producer Caloramator celer as affected by external pH and hydrogen partial pressure
- 2014
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Ingår i: Microbial Cell Factories. - : Springer Science and Business Media LLC. - 1475-2859. ; 13:48, s. 16-48
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Tidskriftsartikel (refereegranskat)abstract
- Background: Caloramator celer is a strict anaerobic, alkalitolerant, thermophilic bacterium capable of converting glucose to hydrogen (H2), carbon dioxide, acetate, ethanol and formate by a mixed acid fermentation. Depending on the growth conditions C. celer can produce H2 at high yields. For a biotechnological exploitation of this bacterium for H2 production it is crucial to understand the factors that regulate carbon and electron fluxes and therefore the final distribution of metabolites to channel the metabolic flux towards the desired product. Results: Combining experimental results from batch fermentations with genome analysis, reconstruction of central carbon metabolism and metabolic flux analysis (MFA), this study shed light on glucose catabolism of the thermophilic alkalitolerant bacterium C. celer. Two innate factors pertaining to culture conditions have been identified to significantly affect the metabolic flux distribution: culture pH and partial pressures of H2 (PH2). Overall, at alkaline to neutral pH the rate of biomass synthesis was maximized, whereas at acidic pH the lower growth rate and the less efficient biomass formation are accompanied with more efficient energy recovery from the substrate indicating high cell maintenance possibly to sustain intracellular pH homeostasis. Higher H2 yields were associated with fermentation at acidic pH as a consequence of the lower synthesis of other reduced by-products such as formate and ethanol. In contrast, PH2 did not affect the growth of C. celer on glucose. At high PH2 the cellular redox state was balanced by rerouting the flow of carbon and electrons to ethanol and formate production allowing unaltered glycolytic flux and growth rate, but resulting in a decreased H2 synthesis. Conclusion: C. celer possesses a flexible fermentative metabolism that allows redistribution of fluxes at key metabolic nodes to simultaneously control redox state and efficiently harvest energy from substrate even under unfavorable conditions (i.e. low pH and high PH2). With the H2 production in mind, acidic pH and low PH2 should be preferred for a high yield-oriented process, while a high productivity-oriented process can be achieved at alkaline pH and high PH2.
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| 14. |
- Claassen, Pieternel, et al.
(författare)
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Non-thermal production of pure hydrogen from biomass: HYVOLUTION
- 2010
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Ingår i: Journal of Cleaner Production. - : Elsevier BV. - 0959-6526. ; 18:Supplement 1, s. 4-8
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Tidskriftsartikel (refereegranskat)abstract
- The objectives and methodology of the EU-funded research project HYVOLUTION devoted to hydrogen production from biomass are reviewed. The main scientific objective of this project is the development of a novel two-stage bioprocess employing thermophilic and phototrophic bacteria, for the cost-effective production of pure hydrogen from multiple biomass feedstocks in small-scale, cost-effective industries. Results are summarised of the work on pretreatment technologies for optimal biodegradation of energy crops and bio-residues, conditions for maximum efficiency in conversion of fermentable biomass to hydrogen and CO2, concepts of dedicated installations for optimal gas cleaning and gas quality protocols, as well as innovative system integration aimed at minimizing energy demand and maximizing product output. The main technological objective is the construction of prototype modules of the plant which, when assembled, form the basis of a blueprint for the whole chain for converting biomass to pure hydrogen. A brief outline is presented of the progress made towards developing reactors for thermophilic hydrogen production, reactors for photoheterotrophic hydrogen production and equipment for optimal gas cleaning procedures.
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| 15. |
- Claassen, PAM, et al.
(författare)
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Utilization of biomass for hydrogen fermentation
- 2005
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Ingår i: Biofuels for fuel cells : renewable energy from biomass fermentation. - 1843390922 ; , s. 221-230
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Bokkapitel (övrigt vetenskapligt/konstnärligt)
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| 16. |
- Hernández, Armando, et al.
(författare)
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Impact of the fermentation parameters pH and temperature on stress resilience of Lactobacillus reuteri DSM 17938
- 2019
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Ingår i: AMB Express. - : Springer Science and Business Media LLC. - 2191-0855. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- This study was undertaken to investigate the impact of culture pH (4.5–6.5) and temperature (32–37 °C) on the stress resilience of Lactobacillus reuteri DSM 17938 during freeze-drying and post freeze-drying exposure to low pH (pH 2)and bile salts. Response-surface methodology analysis revealed that freeze-drying survival rates Ncells after drying/Ncells before drying*100 were linearly related to pH with the highest survival rate of 80% when cells were cultured at pH 6.5 and the lowest was 40% when cells were cultured at pH 4.5. The analysis further revealed that within the chosen temperature range the culture temperature did not significantly affect the freeze-drying survival rate. However, fermentation at pH 4.5 led to better survival rates when rehydrated cells were exposed to low pH shock or bile salts. Thus, the effect of pH onfreeze-drying survival was in contrast to effects on low pH and bile salts stress tolerance. The rationale behind this irreconcilability is based on the responses being dissimilar and are not tuned to each other. Culturing strain DSM17938 at pH values higher than 5.5 could be a useful option to improve the survivability and increase viable cell numbers in the final freeze-dried product. However, the dissimilar responses for the process- and application parameterstested here suggest that an optimal compromise has to be found in order to obtain the most functional probiotic product possible.
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| 17. |
- Hofvendahl, Karin, et al.
(författare)
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Effect of temperature and pH on growth and product formation of Lactococcus lactis ssp. lactis ATCC 19435 growing on maltose
- 1999
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 51:5, s. 669-672
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Tidskriftsartikel (refereegranskat)abstract
- Lactococcus lactis ssp. lactis ATCC 19435 is known to produce mixed acids when grown on maltose. A change in fermentation conditions only, elevated temperatures (up to 37 °C) and reduced pH values (down to 5.0) resulted in a shift towards homolactic product formation. This was accompanied by decreased growth rate and cell yield. The results are discussed in terms of redox balance and maintenance, and the regulation of lactate dehydrogenase and pyruvate formate-lyase.
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| 18. |
- Ioannis, Panagiotopoulos, et al.
(författare)
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Exploring critical factors for fermentative hydrogen production from various types of lignocellulosic biomass
- 2011
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Ingår i: Journal of the Japan Institute of Energy. - : The Japan Institute of Energy. - 1882-6121 .- 0916-8753. ; 90:4, s. 363-368
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Tidskriftsartikel (refereegranskat)abstract
- Four dilute-acid pretreated and hydrolysed lignocellulosic raw materials were evaluated as substrates for fermentative hydrogen production by Caldicellulosiruptor saccharolyticus. Their fermentability was ranked in the order: barley straw > wheat straw > corn stalk > corn cob. The content of 5-hydroxymethylfurfural (HMF) in medium with hydrolysates prepared from corn cob (1.0 g/L) and corn stalk (0.8 g/L), respectively, reached levels likely to be toxic for growth of C. saccharolyticus. HMF was absent in wheat and barley straw hydrolysates. Furfural concentrations in media with wheat straw, barley straw and corn stalk hydrolysates were low (0.2-0.3 g/L), while it was higher in corn cob hydrolysates (0.6 g/L).
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| 19. |
- Kostesha, Natalie, et al.
(författare)
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Probing the redox metabolism in the strictly anaerobic, extremely thermophilic, hydrogen-producing Caldicellulosiruptor saccharolyticus using amperometry
- 2011
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Ingår i: Extremophiles. - : Springer Science and Business Media LLC. - 1433-4909 .- 1431-0651. ; 15:1, s. 77-87
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Tidskriftsartikel (refereegranskat)abstract
- Changes in the redox metabolism in the anaerobic, extremely thermophilic, hydrogen-forming bacterium Caldicellulosiruptor saccharolyticus were probed for the first time in vivo using mediated amperometry with ferricyanide as a thermotolerant external mediator. Clear differences in the intracellular electron flow were observed when cells were supplied with different carbon sources. A higher electrochemical response was detected when cells were supplied with xylose than with sucrose or glucose. Moreover, using the mediated electrochemical method, it was possible to detect differences in the electron flow between cells harvested in the exponential and stationary growth phases. The electron flow of C. saccharolyticus was dependent on the NADH- and reduced ferredoxin generation flux and the competitive behavior of cytosolic and membrane-associated oxidoreductases. Sodium oxamate was used to inhibit the NADH-dependent lactate dehydrogenase, upon which more NADH was directed to membrane-associated enzymes for ferricyanide reduction, leading to a higher electrochemical signal. The method is noninvasive and the results presented here demonstrate that this method can be used to accurately detect changes in the intracellular electron flow and to probe redox enzyme properties of a strictly anaerobic thermophile in vivo.
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| 20. |
- Kristjansdottir, Thordis, et al.
(författare)
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Engineering the carotenoid biosynthetic pathway in Rhodothermus marinus for lycopene production
- 2020
-
Ingår i: Metabolic Engineering Communications. - : Elsevier BV. - 2214-0301. ; 11
-
Tidskriftsartikel (refereegranskat)abstract
- Rhodothermus marinus has the potential to be well suited for biorefineries, as an aerobic thermophile that produces thermostable enzymes and is able to utilize polysaccharides from different 2nd and 3rd generation biomass. The bacterium produces valuable chemicals such as carotenoids. However, the native carotenoids are not established for industrial production and R. marinus needs to be genetically modified to produce higher value carotenoids. Here we genetically modified the carotenoid biosynthetic gene cluster resulting in three different mutants, most importantly the lycopene producing mutant TK-3 (ΔtrpBΔpurAΔcruFcrtB::trpBcrtBT.thermophilus). The genetic modifications and subsequent structural analysis of carotenoids helped clarify the carotenoid biosynthetic pathway in R. marinus. The nucleotide sequences encoding the enzymes phytoene synthase (CrtB) and the previously unidentified 1′,2′-hydratase (CruF) were found fused together and encoded by a single gene in R. marinus. Deleting only the cruF part of the gene did not result in an active CrtB enzyme. However, by deleting the entire gene and inserting the crtB gene from Thermus thermophilus, a mutant strain was obtained, producing lycopene as the sole carotenoid. The lycopene produced by TK-3 was quantified as 0.49 g/kg CDW (cell dry weight).
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| 21. |
- Ljunggren, Mattias, et al.
(författare)
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A kinetic model for quantitative evaluation of the effect of hydrogen and osmolarity on hydrogen production by Caldicellulosiruptor saccharolyticus
- 2011
-
Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 4:31:1, s. 1-15
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Caldicellulosiruptor saccharolyticus has attracted increased interest as an industrial hydrogen (H2)producer. The aim of the present study was to develop a kinetic growth model for this extreme thermophile. The model is based on Monod kinetics supplemented with the inhibitory effects of H2 and osmotic pressure, as well as the liquid-to-gas mass transfer of H2. Results: Mathematical expressions were developed to enable the simulation of microbial growth, substrate consumption and product formation. The model parameters were determined by fitting them to experimental data. The derived model corresponded well with experimental data from batch fermentations in which the stripping rates and substrate concentrations were varied. The model was used to simulate the inhibition of growth by H2 and solute concentrations, giving a critical dissolved H2 concentration of 2.2 mmol/L and an osmolarity of 0.27 to 29 mol/L. The inhibition by H2, being a function of the dissolved H2 concentration, was demonstrated to be mainly dependent on H2 productivity and mass transfer rate. The latter can be improved by increasing the stripping rate, thereby allowing higher H2 productivity. The experimentally determined degree of oversaturation of dissolved H2 was 12 to 34 times the equilibrium concentration and was comparable to the values given by the model. Conclusions: The derived model is the first mechanistically based model for fermentative H2 production and provides useful information to improve the understanding of the growth behavior of C. saccharolyticus. The model can be used to determine optimal operating conditions for H2 production regarding the substrate concentration and the stripping rate.
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| 22. |
- Narayanan, Venkatachalam, et al.
(författare)
-
Adaptation to low pH and lignocellulosic inhibitors resulting in ethanolic fermentation and growth of Saccharomyces cerevisiae
- 2016
-
Ingår i: AMB Express. - : Springer Science and Business Media LLC. - 2191-0855. ; 6
-
Tidskriftsartikel (refereegranskat)abstract
- Lignocellulosic bioethanol from renewable feedstocks using Saccharomyces cerevisiae is a promising alternative tofossil fuels owing to environmental challenges. S. cerevisiae is frequently challenged by bacterial contamination anda combination of lignocellulosic inhibitors formed during the pre-treatment, in terms of growth, ethanol yield andproductivity. We investigated the phenotypic robustness of a brewing yeast strain TMB3500 and its ability to adapt tolow pH thereby preventing bacterial contamination along with lignocellulosic inhibitors by short-term adaptation andadaptive lab evolution (ALE). The short-term adaptation strategy was used to investigate the inherent ability of strainTMB3500 to activate a robust phenotype involving pre-culturing yeast cells in defined medium with lignocellulosicinhibitors at pH 5.0 until late exponential phase prior to inoculating them in defined media with the same inhibitorcocktail at pH 3.7. Adapted cells were able to grow aerobically, ferment anaerobically (glucose exhaustion by 19 ± 5 hto yield 0.45 ± 0.01 g ethanol g glucose−1) and portray significant detoxification of inhibitors at pH 3.7, when comparedto non-adapted cells. ALE was performed to investigate whether a stable strain could be developed to growand ferment at low pH with lignocellulosic inhibitors in a continuous suspension culture. Though a robust populationwas obtained after 3600 h with an ability to grow and ferment at pH 3.7 with inhibitors, inhibitor robustness was notstable as indicated by the characterisation of the evolved culture possibly due to phenotypic plasticity. With furtherresearch, this short-term adaptation and low pH strategy could be successfully applied in lignocellulosic ethanolplants to prevent bacterial contamination.
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| 23. |
- Narayanan, Venkatachalam, et al.
(författare)
-
Increased lignocellulosic inhibitor tolerance of Saccharomyces cerevisiae cell populations in early stationary phase
- 2017
-
Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Production of second-generation bioethanol and other bulk chemicals by yeast fermentation requirescells that tolerate inhibitory lignocellulosic compounds at low pH. Saccharomyces cerevisiae displays high plasticitywith regard to inhibitor tolerance, and adaptation of cell populations to process conditions is essential for reachingefficient and robust fermentations.Results: In this study, we assessed responses of isogenic yeast cell populations in different physiological states tocombinations of acetic acid, vanillin and furfural at low pH. We found that cells in early stationary phase (ESP) exhibitedsignificantly increased tolerance compared to cells in logarithmic phase, and had a similar ability to initiategrowth in the presence of inhibitors as pre-adapted cells. The ESP cultures consisted of subpopulations with differentbuoyant cell densities which were isolated with flotation and analysed separately. These so-called quiescent (Q) andnon-quiescent (NQ) cells were found to possess similar abilities to initiate growth in the presence of lignocellulosicinhibitors at pH 3.7, and had similar viabilities under static conditions. Therefore, differentiation into Q-cells was notthe cause for increased tolerance of ESP cultures. Flow cytometry analysis of cell viability, intracellular pH and reactiveoxygen species levels revealed that tolerant cell populations had a characteristic response upon inhibitor perturbations.Growth in the presence of a combination of inhibitors at low pH correlated with pre-cultures having a highfrequency of cells with low pHiand low ROS levels. Furthermore, only a subpopulation of ESP cultures was able totolerate lignocellulosic inhibitors at low pH, while pre-adapted cell populations displayed an almost uniform high toleranceto the adverse condition. This was in stark contrast to cell populations growing exponentially in non-inhibitorymedium that were uniformly sensitive to the inhibitors at low pH.Conclusions: ESP cultures of S. cerevisiae were found to have high tolerance to lignocellulosic inhibitors at low pH,and were able to initiate growth to the same degree as cells that were pre-adapted to inhibitors at a slightly acidic pH.Carbon starvation may thus be a potential strategy to prepare cell populations for adjacent stressful environmentswhich may be beneficial from a process perspective for fermentation of non-detoxified lignocellulosic substrates atlow pH. Furthermore, flow cytometry analysis of pHiand ROS level distributions in ESP cultures revealed responsesthat were characteristic for populations with high tolerance to lignocellulosic inhibitors. Measurement of populationdistribution responses as described herein may be applied to predict the outcome of environmental perturbationsand thus can function as feedback for process control of yeast fitness during lignocellulosic fermentation.
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| 24. |
- Palmfeldt, Johan, et al.
(författare)
-
The pool of ADP and ATP regulates anaerobic product formation in resting cells of Lactococcus lactis
- 2004
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Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 70:9, s. 5477-5484
-
Tidskriftsartikel (refereegranskat)abstract
- Lactococcus lactis grows homofermentatively on glucose, while its growth on maltose under anaerobic conditions results in mixed acid product formation in which formate, acetate, and ethanol are formed in addition to lactate. Maltose was used as a carbon source to study mixed acid product formation as a function of the growth rate. In batch and nitrogen-limited chemostat cultures mixed acid product formation was shown to be linked to the growth rate, and homolactic fermentation occurred only in resting cells. Two of the four lactococcal strains investigated with maltose, L. lactis 65.1 and MG1363, showed more pronounced mixed acid product formation during growth than L. lactis ATCC 19435 or IL-1403. In resting cell experiments all four strains exhibited homolactic fermentation. In resting cells the intracellular concentrations of ADP, ATP, and fructose 1,6-bisphosphate were increased and the concentration of P-i was decreased compared with the concentrations in growing cells. Addition of an ionophore (monensin or valinomycin) to resting cultures of L. lactis 65.1 induced mixed acid product formation concomitant with decreases in the ADP, ATP, and fructose 1,6-bisphosphate concentrations. ADP and ATP were shown to inhibit glyceraldehyde-3-phosphate dehydrogenase, lactate dehydrogenase, and alcohol dehydrogenase in vitro. Alcohol dehydrogenase was the most sensitive enzyme and was totally inhibited at an adenine nucleotide concentration of 16 mM, which is close to the sum of the intracellular concentrations of ADP and ATP of resting cells. This inhibition of alcohol dehydrogenase might be partially responsible for the homolactic behavior of resting cells. A hypothesis regarding the level of the ATP-ADP pool as a regulating mechanism for the glycolytic flux and product formation in L. lactis is discussed
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| 25. |
- Pawar, Sudhanshu, et al.
(författare)
-
Biofilm formation by designed co-cultures of Caldicellulosiruptor species as a means to improve hydrogen productivity
- 2015
-
Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Background: Caldicellulosiruptor species have gained a reputation as being among the best microorganisms to produce hydrogen (H2) due to possession of a combination of appropriate features. However, due to their low volumetric H2 productivities (QH2), Caldicellulosiruptor species cannot be considered for any viable biohydrogen production process yet. In this study, we evaluate biofilm forming potential of pure and co-cultures of Caldicellulosiruptor saccharolyticus and Caldicellulosiruptor owensensis in continuously stirred tank reactors (CSTR) and up-flow anaerobic (UA) reactors. We also evaluate biofilms as a means to retain biomass in the reactor and its influence on QH2. Moreover, we explore the factors influencing the formation of biofilm. Results: Co-cultures of C. saccharolyticus and C. owensensis form substantially more biofilm than formed by C. owensensis alone. Biofilms improved substrate conversion in both of the reactor systems, but improved the QH2 only in the UA reactor. When grown in the presence of each other’s culture supernatant, both C. saccharolyticus and C. owensensis were positively influenced on their individual growth and H2 production. Unlike the CSTR, UA reactors allowed retention of C. saccharolyticus and C. owensensis when subjected to very high substrate loading rates. In the UA reactor, maximum QH2 (approximately 20 mmol · L−1 · h−1) was obtained only with granular sludge as the carrier material. In the CSTR, stirring negatively affected biofilm formation. Whereas, a clear correlation was observed between elevated (>40 μM) intracellular levels of the secondary messenger bis-(3′-5′)-cyclic dimeric guanosine monophosphate (c-di-GMP) and biofilm formation. Conclusions: In co-cultures C. saccharolyticus fortified the trade of biofilm formation by C. owensensis, which was mediated by elevated levels of c-di-GMP in C. owensensis. These biofilms were effective in retaining biomass of both species in the reactor and improving QH2 in a UA reactor using granular sludge as the carrier material. This concept forms a basis for further optimizing the QH2 at laboratory scale and beyond.
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| 26. |
- Pawar, Sudhanshu, et al.
(författare)
-
Biohydrogen production from wheat straw hydrolysate using Caldicellulosiruptor saccharolyticus followed by biogas production in a two-step uncoupled process
- 2013
-
Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 1879-3487 .- 0360-3199. ; 38:22, s. 9121-9130
-
Tidskriftsartikel (refereegranskat)abstract
- A two-step, un-coupled process producing hydrogen (H2) from wheat straw using Caldicellulosiruptor saccharolyticus in a ‘Continuously stirred tank reactor’ (CSTR) followed by anaerobic digestion of its effluent to produce methane (CH4) was investigated. C. saccharolyticus was able to convert wheat straw hydrolysate to hydrogen at maximum production rate of approximately 5.2 L H2/L/Day. The organic compounds in the effluent collected from the CSTR were successfully converted to CH4 through anaerobic digestion performed in an ‘Up-flow anaerobic sludge bioreactor’ (UASB) reactor at a maximum production rate of 2.6 L CH4/L/day. The maximum energy output of the process (10.9 kJ/g of straw) was about 57% of the total energy, and 67% of the energy contributed by the sugar fraction, contained in the wheat straw. Sparging the hydrogenogenic CSTR with the flue gas of the UASB reactor ((60% v/v) CH4 and (40% v/v) CO2) decreased the H2 production rate by 44%, which was due to the significant presence of CO2. The presence of CH4 alone, like N2, was indifferent to growth and H2 production by C. saccharolyticus. Hence, sparging with upgraded CH4 would guarantee successful hydrogen production from lignocellulosic biomass prior to anaerobic digestion and thus, reasonably high conversion efficiency can be achieved.
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| 27. |
- Pawar, Sudhanshu, et al.
(författare)
-
Biological hydrogen production from lignocellulosic biomass
- 2015
-
Ingår i: Enriched methane : the first step towards the hydrogen economy. - Cham : Springer International Publishing. - 1865-3529. - 9783319221922 - 9783319221915 ; , s. 111-127
-
Bokkapitel (refereegranskat)abstract
- Biologically derived hydrogen (biohydrogen) from lignocellulosic biomass has the potential to be an ideal renewable fuel as its combustion does not produce carbon-based emissions and it can be derived from sources which do not affect food production. Moreover, the by-products of biohydrogen production can be fed to an anaerobic digester producing biogas. Thus, a two-step process involving biohydrogen production followed by biogas production is emerging as a viable option for conversion of lignocellulosic biomass. Essential aspects of designing a viable hydrogen production system such as biomass selection, inhibitory compounds in the biomass, removal and salvage of hydrogen and the desirable qualities in any hydrogen producing organism are discussed in this chapter.
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| 28. |
- Pawar, Sudhanshu, et al.
(författare)
-
Evaluation of assimilatory sulphur metabolism in Caldicellulosiruptor saccharolyticus
- 2014
-
Ingår i: Bioresource Technology. - : Elsevier BV. - 1873-2976 .- 0960-8524. ; 169, s. 677-685
-
Tidskriftsartikel (refereegranskat)abstract
- Caldicellulosiruptor saccharolyticus has gained reputation as being among the best microorganisms to produce H2 due to possession of various appropriate features. The quest to develop an inexpensive cultivation medium led to determine a possible replacement of the expensive component cysteine, i.e. sulphate. C. saccharolyticus assimilated sulphate successfully in absence of a reducing agent without releasing hydrogen sulphide. A complete set of genes coding for enzymes required for sulphate assimilation were found in the majority of Caldicellulosiruptor species including C. saccharolyticus. C. saccharolyticus displayed indifferent physiological behaviour to source of sulphur when grown under favourable conditions in continuous cultures. Increasing the usual concentration of sulphur in the feed medium increased substrate conversion. Choice of sulphur source did not affect the tolerance of C. saccharolyticus to high partial pressures of H2. Thus, sulphate can be a principle sulphur source in an economically viable and more sustainable biohydrogen process using C. saccharolyticus.
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| 29. |
- Pawar, Sudhanshu, et al.
(författare)
-
Thermophilic biohydrogen production: how far are we?
- 2013
-
Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 97:18, s. 7999-8009
-
Forskningsöversikt (refereegranskat)abstract
- Apart from being applied as an energy carrier, hydrogen is in increasing demand as a commodity. Currently, the majority of hydrogen (H2) is produced from fossil fuels, but from an environmental perspective, sustainable H2 production should be considered. One of the possible ways of hydrogen production is through fermentation, in particular, at elevated temperature, i.e. thermophilic biohydrogen production. This short review recapitulates the current status in thermophilic biohydrogen production through fermentation of commercially viable substrates produced from readily available renewable resources, such as agricultural residues. The route to commercially viable biohydrogen production is a multidisciplinary enterprise. Microbiological studies have pointed out certain desirable physiological characteristics in H2-producing microorganisms. More process-oriented research has identified best applicable reactor types and cultivation conditions. Techno-economic and life cycle analyses have identified key process bottlenecks with respect to economic feasibility and its environmental impact. The review has further identified current limitations and gaps in the knowledge, and also deliberates directions for future research and development of thermophilic biohydrogen production.
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| 30. |
- Ron, Emanuel, et al.
(författare)
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Characterization of carotenoids in Rhodothermus marinus
- 2018
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Ingår i: MicrobiologyOpen. - : Wiley. - 2045-8827. ; 7:1
-
Tidskriftsartikel (refereegranskat)abstract
- Rhodothermus marinus, a marine aerobic thermophile, was first isolated from an intertidal hot spring in Iceland. In recent years, the R. marinus strain PRI 493 has been genetically modified, which opens up possibilities for targeted metabolic engineering of the species, such as of the carotenoid biosynthetic pathway. In this study, the carotenoids of the R. marinus type-strain DSM 4252T, strain DSM 4253, and strain PRI 493 were characterized. Bioreactor cultivations were used for pressurized liquid extraction and analyzed by ultra-high performance supercritical fluid chromatography with diode array and quadropole time-of-flight mass spectrometry detection (UHPSFC-DAD-QTOF/MS). Salinixanthin, a carotenoid originally found in Salinibacter ruber and previously detected in strain DSM 4253, was identified in all three R. marinus strains, both in the hydroxylated and nonhydroxylated form. Furthermore, an additional and structurally distinct carotenoid was detected in the three strains. MS/MS fragmentation implied that the mass difference between salinixanthin and the novel carotenoid structure corresponded to the absence of a 4-keto group on the ß-ionone ring. The study confirmed the lack of carotenoids for the strain SB-71 (ΔtrpBΔpurAcrtBI’::trpB) in which genes encoding two enzymes of the proposed pathway are partially deleted. Moreover, antioxidant capacity was detected in extracts of all the examined R. marinus strains and found to be 2–4 times lower for the knock-out strain SB-71. A gene cluster with 11 genes in two operons in the R. marinusDSM 4252T genome was identified and analyzed, in which several genes were matched with carotenoid biosynthetic pathway genes in other organisms.
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| 31. |
- Ron, Emanuel Y C, et al.
(författare)
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Cultivation technology development of Rhodothermus marinus DSM 16675
- 2019
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Ingår i: Extremophiles : life under extreme conditions. - : Springer Science and Business Media LLC. - 1433-4909. ; 23:6, s. 735-745
-
Tidskriftsartikel (refereegranskat)abstract
- This work presents an evaluation of batch, fed-batch, and sequential batch cultivation techniques for production of R. marinus DSM 16675 and its exopolysaccharides (EPSs) and carotenoids in a bioreactor, using lysogeny broth (LB) and marine broth (MB), respectively, in both cases supplemented with 10 g/L maltose. Batch cultivation using LB supplemented with maltose (LBmalt) resulted in higher cell density (OD620 = 6.6) than use of MBmalt (OD620 = 1.7). Sequential batch cultivation increased the cell density threefold (OD620 = 20) in LBmalt and eightfold (OD620 = 14) in MBmalt. In both single and sequential batches, the production of carotenoids and EPSs using LBmalt was detected in the exponential phase and stationary phase, respectively, while in MBmalt formation of both products was detectable in both the exponential and stationary phases of the culture. Heteropolymeric EPSs were produced with an overall volumetric productivity (QE) of 0.67 (mg/L h) in MBmalt and the polymer contained xylose. In LB, QE was lower (0.1 mg/L h) and xylose could not be detected in the composition of the produced EPSs. In conclusion, this study showed the importance of a process design and medium source for production of R. marinus DSM 16675 and its metabolites.
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| 32. |
- Seshagiri Rao, Nikhil, et al.
(författare)
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Non-inhibitory levels of oxygen during cultivation increase freeze-drying stress tolerance in Limosilactobacillus reuteri DSM 17938
- 2023
-
Ingår i: Frontiers in Microbiology. - 1664-302X. ; 14
-
Tidskriftsartikel (refereegranskat)abstract
- The physiological effects of oxygen on Limosilactobacillus reuteri DSM 17938 during cultivation and the ensuing properties of the freeze-dried probiotic product was investigated. On-line flow cytometry and k-means clustering gating was used to follow growth and viability in real time during cultivation. The bacterium tolerated aeration at 500 ml/min, with a growth rate of 0.74 ± 0.13 h-1 which demonstrated that low levels of oxygen did not influence the growth kinetics of the bacterium. Modulation of the redox metabolism was, however, seen already at non-inhibitory oxygen levels by 1.5-fold higher production of acetate and 1.5-fold lower ethanol production. A significantly higher survival rate in the freeze-dried product was observed for cells cultivated in presence of oxygen compared to absence of oxygen (61.8 ± 2.4 % vs 11.5 ± 4.3 %), coinciding with a higher degree of unsaturated fatty acids (UFA:SFA ratio of 10 for air sparged vs 3.59 for N2 sparged conditions.). Oxygen also resulted in improved bile tolerance and boosted 5’nucleotidase activity (370 U/L vs 240 U/L in N2 sparged conditions) but lower tolerance to acidic conditions compared bacteria grown under complete anaerobic conditions which survived up to 90 min of exposure at pH 2. Overall, our results indicate the controlled supply of oxygen during production may be used as means for probiotic activity optimisation of L. reuteri DSM 17938.
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| 33. |
- Skorupa Parachin, Nadia, et al.
(författare)
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Kinetic modelling reveals current limitations in the production of ethanol from xylose by recombinant Saccharomyces cerevisiae.
- 2011
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Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176. ; 13, s. 508-517
-
Tidskriftsartikel (refereegranskat)abstract
- Saccharomyces cerevisiae lacks the ability to ferment the pentose sugar xylose that is the second most abundant sugar in nature. Therefore two different xylose catabolic pathways have been heterologously expressed in S. cerevisiae. Whereas the xylose reductase (XR)-xylitol dehydrogenase (XDH) pathway leads to the production of the by-product xylitol, the xylose isomerase (XI) pathway results in significantly lower xylose consumption. In this study, kinetic models including the reactions ranging from xylose transport into the cell to the phosphorylation of xylulose to xylulose 5-P were constructed. They were used as prediction tools for the identification of putative targets for the improvement of xylose utilization in S. cerevisiae strains engineered for higher level of the non-oxidative pentose phosphate pathway (PPP) enzymes, higher xylulokinase and inactivated GRE3 gene encoding an endogenous NADPH-dependent aldose reductase. For both pathways, the in silico analyses identified a need for even higher xylulokinase (XK) activity. In a XR-XDH strain expressing an integrated copy of the Escherichia coli XK encoding gene xylB about a six-fold reduction of xylitol formation was confirmed under anaerobic conditions. Similarly overexpression of the xylB gene in a XI strain increased the aerobic growth rate on xylose by 21%. In contrast to the in silico predictions, the aerobic growth also increased 24% when the xylose transporter gene GXF1 from Candida intermedia was overexpressed together with xylB in the XI strain. Under anaerobic conditions, the XI strains overexpressing xylB gene and the combination of xylB and GFX1 genes consumed 27% and 37% more xylose than the control strain.
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| 34. |
- Soto, Luis Romero, et al.
(författare)
-
Hydrogen and polyhydroxybutyrate production from wheat straw hydrolysate using Caldicellulosiruptor species and Ralstonia eutropha in a coupled process
- 2019
-
Ingår i: Bioresource Technology. - : Elsevier BV. - 0960-8524. ; 272, s. 259-266
-
Tidskriftsartikel (refereegranskat)abstract
- This report presents an integrated biorefinery concept in which wheat straw hydrolysate was treated with co-cultures of osmotolerant thermophilic bacterial strains, Caldicellulosiruptor saccharolyticus and C. owensensis to obtain hydrogen, while the liquid effluent containing acetate and residual glucose was used as feed for polyhydroxybutyrate (PHB) production by Ralstonia eutropha. The Caldicellulosiruptor spp. co-culture consumed 10.8 g/L of pretreated straw sugars, glucose and xylose, producing 134 mmol H2/L. PHB accumulation by R. eutropha was first studied in minimal salts medium using acetate with/without glucose as carbon source. Addition of salts promoted cell growth and PHB production in the effluent. Fed-batch cultivation in a nitrogen limited medium with 40% (v/v) aeration resulted in a cell density of 15.1 g/L with PHB content of 80.1% w/w and PHB concentration of 12.1 g/L, while 20% aeration gave a cell density of 11.3 g/L with 83.4% w/w PHB content and 9.4 g/L PHB concentration.
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| 35. |
- Sreenivas, Krishnan, et al.
(författare)
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Evaluation of Pyrophosphate‐Driven Proton Pumps in Saccharomyces cerevisiae under Stress Conditions
- 2024
-
Ingår i: Microorganisms. - 2076-2607. ; 12:3
-
Tidskriftsartikel (refereegranskat)abstract
- In Saccharomyces cerevisiae, pH homeostasis is reliant on ATP due to the use of proton-translocating ATPase (H+-ATPase) which constitutes a major drain within cellular ATP supply. Here, an exogenous proton-translocating pyrophosphatase (H+-PPase) from Arabidopsis thaliana, which uses inorganic pyrophosphate (PPi) rather than ATP, was evaluated for its effect on reducing the ATP burden. The H+-Ppase was localized to the vacuolar membrane or to the cell membrane, and their impact was studied under acetate stress at a low pH. Biosensors (pHluorin and mQueen-2m) were used to observe changes in intracellular pH (pHi) and ATP levels during growth on either glucose or xylose. A significant improvement of 35% in the growth rate at a pH of 3.7 and 6 g·L−1 acetic acid stress was observed in the vacuolar membrane H+-PPase strain compared to the parent strain. ATP levels were elevated in the same strain during anaerobic glucose and xylose fermentations. During anaerobic xylose fermentations, co-expression of pHluorin and a vacuolar membrane H+-PPase improved the growth characteristics by means of an improved growth rate (11.4%) and elongated logarithmic growth duration. Our study identified a potential method for improving productivity in the use of S. cerevisiae as a cell factory under the harsh conditions present in industry.
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| 36. |
- van Niel, Ed
(författare)
-
Biological processes for hydrogen production
- 2016
-
Ingår i: Anaerobes in Biotechnology. - Berlin, Heidelberg : Springer Berlin Heidelberg. - 9783319456515 ; , s. 1-39
-
Bokkapitel (refereegranskat)abstract
- Methane is produced usually from organic waste in a straightforward anaerobic digestion process. However, hydrogen production is technically more challenging as more stages are needed to convert all biomass to hydrogen because of thermodynamic constraints. Nevertheless, the benefit of hydrogen is that it can be produced, both biologically and thermochemically, in more than one way from either organic compounds or water. Research in biological hydrogen production is booming, as reflected by the myriad of recently published reviews on the topic. This overview is written from the perspective of how to transfer as much energy as possible from the feedstock into the gaseous products hydrogen, and to a lesser extent, methane. The status and remaining challenges of all the biological processes are concisely discussed.
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| 37. |
- van Niel, Ed, et al.
(författare)
-
Close to the edge: growth restrained by the NAD(P)H/ATP formation flux ratio
- 2017
-
Ingår i: Frontiers in Microbiology. - : Frontiers Media SA. - 1664-302X. ; 8
-
Tidskriftsartikel (refereegranskat)abstract
- Most fermentative microorganisms grow well-under anaerobic conditions managing a balanced redox and appropriate energy metabolism, but a few species do exist in which cells have to cope with inadequate energy recovery or capture and/or redox balancing. Two cases of these species, i.e., the metabolically engineered Saccharomyces cerevisiae enabling it to ferment xylose and Lactobacillus reuteri fermenting glucose via the phosphoketolase pathway, are here used to introduce a quantification parameter to capture what limits the growth rate of these microorganisms under anaerobic conditions. This dimensionless parameter, the cofactor formation flux ratio (RJ), is the ratio between the redox formation flux (JNADH+NADPH), and the energy carrier formation flux (JATP), which are mainly connected to the central carbon pathways. Data from metabolic flux analyses performed in previous and present studies were used to estimate the RJ-values. Even though both microorganisms possess different central pathways, a similar relationship between RJ and the specific growth rate (μ) was found. Furthermore, for both microorganisms external electron acceptors moderately reduced the RJ-value,thereby raising the μ accordingly. Based on the emerging profile of this relationship an interpretation is presented suggesting that this quantitative analysis can be applied beyond the two microbial species experimentally investigated in the current study to provide data for future targeted strain development strategies.
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| 38. |
- van Niel, Ed, et al.
(författare)
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Effect of carbon dioxide and temperature on H2 producing cultures of the extreme thermophile, Caldicellulosiruptor saccharolyticus
- 2004
-
Ingår i: Proceedings of the 15th World Hydrogen Energy Conference.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Carbon dioxide could replace nitrogen gas as stripping gas for the production of H2 by the extreme thermophile, Caldicellulosiruptor saccharolyticus, provided that the pH is kept below 7.0. Above this pH, ≥77 mM sodium bicarbonate will be introduced as an extra salt burden to the culture. High concentrations of sugars and salts contribute each to the inhibition of growth and H2 production, which is most probably due to the osmolality. As a consequence, using CO2 as stripping gas might lower the maximum allowable acetate concentration in culture, and therefore the productivity of the culture at neutral pH. Although the growth rate was not affected by CO2, lower biomass and hydrogen yields were obtained. This could be due to an increased lactate production. In a thermodynamic study an estimation of the activation enthalpies was made for both hydrogen production and its thermal inactivation, being 45.9 kJ/mol and 112.3 kJ/mol, respectively. Hydrogen production showed a wider temperature range (estimated 40 - 90° C) than growth (49.6 – 85.7° C).
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| 39. |
- van Niel, Ed, et al.
(författare)
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Formation and conversion of oxygen metabolites by Lactococcus lactis subsp lactis ATCC 19435 under different growth conditions
- 2002
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Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 68:9, s. 4350-4356
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Tidskriftsartikel (refereegranskat)abstract
- A semidefined medium based on Casamino Acids allowed Lactococcus lactis ATCC 19435 to grow in the presence of oxygen at a slow rate (0.015 h(-1)). Accumulation of H2O2 in the culture prevented a higher growth rate. Addition of asparagine to the medium increased the growth rate; whereby H2O2 accumulated only temporarily during the lag phase. H2O2 is an inhibitor for several glycolytic enzymes, glyceraldehyde-3-phosphate dehydrogenase being the most sensitive. Strain ATCC 19435 contained NADH oxidase (maximum specific rate under aerobic conditions, 426 nmol of NADH min(-1) mg of protein(-1)), which reduced oxygen to water, whereby superoxide was formed as a by-product. H2O2 originated from the dismutation of superoxide by superoxide dismutase. Although H2O2, was rapidly destroyed under high metabolic fluxes, neither NADH peroxidase nor any other enzymatic H2O2-reducing activity was detected. However, pyruvate, the end product of glycolysis; reacted nonenzymatically and rapidly with H2O2 and hence was a potential alternative for scavenging of this oxygen metabolite intracellularly. Indeed, intracellular concentrations of up to 93 mM pyruvate were detected in aerobic cultures growing at high rates. It is hypothesized that self-generated pyruvate may serve to protect L. lactis strain ATCC 19435 from H2O2.
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| 40. |
- van Niel, Ed, et al.
(författare)
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Hydrogen production by thermophilic fermentation
- 2011
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Ingår i: State of the art and progress in production of biohydrogen. - : BENTHAM SCIENCE PUBLISHERS. - 9781608054114 ; , s. 137-159
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Bokkapitel (refereegranskat)abstract
- Of the many ways hydrogen can be produced, this chapter focuses on biological hydrogen production 12 by thermophilic bacteria and archaea in dark fermentations. The thermophiles are held as promising candidates 13 for a cost-effective fermentation process, because of their relatively high yields and broad substrate palette. Yet 14 many challenges remain to be faced, including improving productivity, tolerance to high osmolality and growth 15 inhibitors, and reactor configuration. This review consolidates current insights in the quest for high yields and 16 productivities within thermophilic hydrogen production. Important is to understand how environmental 17 parameters affect the redox- and energy metabolism of the microorganism(s) involved. This knowledge is 18 required for designing an optimal bioreactor configuration and operation.
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| 41. |
- van Niel, Ed, et al.
(författare)
-
) Inhibition of anaerobic phosphate release by nitric oxide in activated sludge
- 1998
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Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 64:8, s. 2925-2930
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Tidskriftsartikel (refereegranskat)abstract
- Activated sludge not containing significant numbers of denitrifying, polyphosphate [poly(P)]-accumulating bacteria was grown in a fill-and-draw system and exposed to alternating anaerobic and aerobic periods. During the aerobic period, poly(P) accumulated up to 100 mg of P · g of (dry) weight. When portions of the sludge were incubated anaerobically in the presence of acetate, 80 to 90% of the intracellular poly(P) was degraded and released as orthophosphate. Degradation of poly(P) was mainly catalyzed by the concerted action of polyphosphate:AMP phosphotransferase and adenylate kinase, resulting in ATP formation. In the presence of 0.3 mM nitric oxide (NO) in the liquid-phase release of phosphate, uptake of acetate, formation of poly-β-hydroxybutyrate, utilization of glycogen, and formation of ATP were severely inhibited or completely abolished. In cell extracts of the sludge, adenylate kinase activity was completely inhibited by 0.15 mM NO. The nature of this inhibition was probably noncompetitive, similar to that with hog adenylate kinase. Activated sludge polyphosphate glucokinase was also completely inhibited by 0.15 mM NO. It is concluded that the inhibitory effect of NO on acetate-mediated phosphate release by the sludge used in this study is due to the inhibition of adenylate kinase in the phosphate-releasing organisms. The inhibitory effect of nitrate and nitrite on phosphate release is probably due to their conversion to NO. The lack of any inhibitory effect of NO on adenylate kinase of the poly(P)-accumulatingAcinetobacter johnsonii 210A suggests that this type of organism is not involved in the enhanced biological phosphate removal by the sludges used.
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| 42. |
- van Niel, Ed, et al.
(författare)
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Nutrient requirements of lactococci in defined growth media
- 1999
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 52:5, s. 617-627
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Forskningsöversikt (refereegranskat)abstract
- Many attempts have been made for the last six decades to design defined media for species of the lactococcus group. The general outcome of the studies suggests that this group is heterogeneous with respect to specific requirements for nutrients. Lactococcal species are limited in various metabolic pathways. Early attempts to trace the required nutrients were not always successful because of the poor quality of analysis and the presence of impurities in the medium components.
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| 43. |
- van Niel, Ed, et al.
(författare)
-
Physiology of chemoheterotrophic thermoanaerobes
- 2023
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Ingår i: Thermophilic Anaerobes : Phylogeny, Physiology and Biotechnological Applications - Phylogeny, Physiology and Biotechnological Applications. - 9783031417191 - 9783031417207 ; , s. 133-151
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Bokkapitel (refereegranskat)abstract
- The industry is increasingly discovering the potential of strict anaerobic thermophilic bacteria, as there are many applications to consider, including the production of stable thermozymes and degradation of lignocellulosic materials, proteins, and alkanes. However, the metabolism of these thermoanaerobes is still poorly understood and so far, there is comprehensive knowledge of only a few model species. Of the studies published to date, the vast majority have focused almost exclusively on the anaerobic catabolism of carbohydrates, including polysaccharides, hexoses, pentoses, and disaccharides. While research on the fermentation of proteins and amino acids has enjoyed some recent developments, the exploration of the degradation of lipids and alkanes under these conditions has only just begun. In this chapter, the different central carbon pathways are discussed along with the utilization of alternative intracellular energy carriers other than ATP, namely GTP and pyrophosphate. Subsequent steps and approaches in deeper understanding of the physiology are concisely discussed.
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| 44. |
- van Niel, Ed, et al.
(författare)
-
Production of biofuels by thermoanaerobic bacteria
- 2023
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Ingår i: Thermophilic Anaerobes : Phylogeny, Physiology and Biotechnological Applications - Phylogeny, Physiology and Biotechnological Applications. - 9783031417191 - 9783031417207 ; , s. 187-208
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Bokkapitel (refereegranskat)abstract
- Biofuel demand is gradually rising yearly and is expected to do so more rapidly due to the current energy crisis. Bioethanol production is already at a commercial scale but is primarily made using mesophiles fermenting corn and sugar, which have obvious societal drawbacks. Therefore, new technologies should be developed. In addition, hydrogen as a non-carbon energy carrier has gained renewed interest. Thermophilic hydrogen and ethanol production from lignocellulosics and organic wastes, therefore, provide new avenues of biofuel production. This overview looks concisely into the status and remaining challenges of hydrogen and ethanol production exploiting thermophilic anaerobic bacteria.
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| 45. |
- van Niel, Ed, et al.
(författare)
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Reappraisal of the regulation of lactococcal L-lactate dehydrogenase
- 2004
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Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 70:3, s. 1843-1846
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Tidskriftsartikel (refereegranskat)abstract
- Lactococcal lactate dehydrogenases (LDHs) are coregulated at the substrate level by at least two mechanisms: the fructose- 1,6-biphosphate/phosphate ratio and the NADH/NAD ratio. Among the Lactococcus lactis species, there are strains that are predominantly regulated by the first mechanism (e.g., strain 65.1) or by the second mechanism (e.g., strain NCDO 2118). A more complete model of the kinetics of the regulation of lactococcal LDH is discussed.
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| 46. |
- van Niel, Ed, et al.
(författare)
-
Substrate and product inhibition of hydrogen production by the extreme thermophile, Caldicellulosiruptor saccharolyticus.
- 2003
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Ingår i: Biotechnology and Bioengineering. - : Wiley. - 1097-0290 .- 0006-3592. ; 81:3, s. 255-262
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Tidskriftsartikel (refereegranskat)abstract
- Substrate and product inhibition of hydrogen production during sucrose fermentation by the extremely thermophilic bacterium Caldicellulosiruptor saccharolyticus was studied. The inhibition kinetics were analyzed with a noncompetitive, nonlinear inhibition model. Hydrogen was the most severe inhibitor when allowed to accumulate in the culture. Concentrations of 5-10 mM H2 in the gas phase ( partial hydrogen pressure (pH2) of (1-2) · 104 Pa) initiated a metabolic shift to lactate formation. The extent of inhibition by hydrogen was dependent on the density of the culture. The highest tolerance for hydrogen was found at low volumetric hydrogen production rates, as occurred in cultures with low cell densities. Under those conditions the critical hydrogen concentration in the gas phase was 27.7 mM H2 ( pH2 of 5.6 · 104 Pa); above this value hydrogen production ceased completely. With an efficient removal of hydrogen sucrose fermentation was mainly inhibited by sodium acetate. The critical concentrations of sucrose and acetate, at which growth and hydrogen production was completely inhibited (at neutral pH and 70°C), were 292 and 365 mM, respectively. Inorganic salts, such as sodium chloride, mimicked the effect of sodium acetate, implying that ionic strength was responsible for inhibition. Undissociated acetate did not contribute to inhibition of cultures at neutral or slightly acidic pH. Exposure of exponentially growing cultures to concentrations of sodium acetate or sodium chloride higher than ca. 175 mM caused cell lysis, probably due to activation of autolysins. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 81: 255-262, 2003.
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| 47. |
- van Niel, Ed, et al.
(författare)
-
The potential of biodetoxification activity as a probiotic property of Lactobacillus reuteri.
- 2012
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Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605. ; 152, s. 206-210
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Tidskriftsartikel (refereegranskat)abstract
- Previous work on the metabolism of Lactobacillus reuteri ATCC 55730 anticipated a variability in the use of organic electron acceptors as a means to relieve metabolic redox problems. Therefore, investigations focusing on this unique metabolism of L. reuteri may reveal a basis for new probiotic properties. For instance, L. reuteri may use reactive aldehydes and ketones as electron acceptors to balance their redox metabolism, which opens the possibility to exploit this bacterium for in vivo bioreduction of deleterious compounds in the gastrointestinal tract (GIT). Herein we demonstrate that L. reuteri ATCC 55730 cultures on glucose are able to use furfural (1g/L), and hydroxymethylfurfural (HMF) (0.5g/L), as electron acceptors. The former enhances the growth rate by about 25% and biomass yield by 15%, whereas the latter is inhibitory. Furfural is stoichiometrically reduced to furfuryl alcohol by the culture. The conversion of furfural had no effect on the flux distribution between the simultaneously operating phosphoketolase and Embden-Meyerhof pathways, but initiated a flux to acetate production. In addition to furfural and HMF, cellular extracts showed potential to reoxidize NADH and/or NADPH with acrolein, crotonaldehyde, and diacetyl, indicating that conversion reactions take place intracellularly, however, utilization mechanisms for the latter compounds may not be present in this strain. The strain did not reduce other GIT-related reactive compounds, including acrylamide, glyoxal, and furan.
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| 48. |
- Velasco, Susana, et al.
(författare)
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Environmental factors influencing growth of and exopolysaccharide formation by Pediococcus parvulus 2.6
- 2006
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Ingår i: International Journal of Food Microbiology. - : Elsevier BV. - 0168-1605. ; 111:3, s. 252-258
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Tidskriftsartikel (refereegranskat)abstract
- Natural exopolysaccharides (EPSs) from food-grade lactic acid bacteria have potential for development and exploitation as food additives and functional food ingredients with both health and economic benefits. In this study, we have examined the physiological capacity of EPS production in Pediococcus parvulus 2.6. EPS formation by P. parvulus 2.6 was found to be linked to biomass yields, provided that glucose was not limiting. Higher biomass yields and EPS productions were obtained when cultures were pH-controlled at pH 5.2. Various compounds have been tested for their influence on growth rate and EPS formation. Of those, only glucose (up to 75 g 1(-1)), ethanol (up to 4.9%, w/v) and glycerol (up to 6.6%, w/v) had positive effects on EPS production. EPS production was not directly linked to growth, because its production continued in the stationary phase provided that glucose was present. According to an empirical model, the growth of R parvulus 2.6 was completely inhibited by 58.9 +/- 18.1 gl(-1) lactate. Lactate, the sole fermentation product, was suggested to affect growth by chelation of manganese. The organism grew in an apparent linear fashion due to this imposed manganese limitation. This could be overcome by increasing the manganese concentration to at least 2 mg l(-1) in the medium. The excretion of Mn2+ upon depletion of glucose indicated that maintenance of the high Mn2+ gradient over the cell membrane is an energy requiring process. EPS production was increased from 0.12 gl(-1) to 4.10 gl(-1) in an improved medium that is based on the results from this study. (c) 2006 Elsevier B.V. All rights reserved.
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| 49. |
- Vongkampang, Thitiwut, et al.
(författare)
-
Characterization of simultaneous uptake of xylose and glucose in Caldicellulosiruptor kronotskyensis for optimal hydrogen production
- 2021
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Ingår i: Biotechnology for Biofuels. - : Springer Science and Business Media LLC. - 1754-6834. ; 14
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Tidskriftsartikel (refereegranskat)abstract
- Background: Caldicellulosiruptor kronotskyensis has gained interest for its ability to grow on various lignocellulosic biomass. The aim of this study was to investigate the growth profles of C. kronotskyensis in the presence of mixtures of glucose–xylose. Recently, we characterized a diauxic-like pattern for C. saccharolyticus on lignocellulosic sugar mixtures. In this study, we aimed to investigate further whether C. kronotskyensis has adapted to uptake glucose in the disaccharide form (cellobiose) rather than the monosaccharide (glucose).Results: Interestingly, growth of C. kronotskyensis on glucose and xylose mixtures did not display diauxic-like growth patterns. Closer investigation revealed that, in contrast to C. saccharolyticus, C. kronotskyensis does not possess a second uptake system for glucose. Both C. saccharolyticus and C. kronotskyensis share the characteristics of preferring xylose over glucose. Growth on xylose was twice as fast (μmax=0.57 h−1) as on glucose (μmax=0.28 h−1). A study of the sugar uptake was made with diferent glucose–xylose ratios to fnd a kinetic relationship between the two sugars for transport into the cell. High concentrations of glucose inhibited xylose uptake and vice versa. The inhibition constants were estimated to be KI,glu=0.01 cmol L−1 and KI,xyl=0.001 cmol L−1, hence glucose uptake was more severely inhibited by xylose uptake. Bioinformatics analysis could not exclude that C. kronotskyensis possesses more than one transporter for glucose. As a next step it was investigated whether glucose uptake by C. kronotskyensis improved in the form of cellobiose. Indeed, cellobiose is taken up faster than glucose; nevertheless, the growth rate on each sugar remained similar.Conclusions: C. kronotskyensis possesses a xylose transporter that might take up glucose at an inferior rate even in the absence of xylose. Alternatively, glucose can be taken up in the form of cellobiose, but growth performance is still inferior to growth on xylose. Therefore, we propose that the catabolism of C. kronotskyensis has adapted more strongly to pentose rather than hexose, thereby having obtained a specifc survival edge in thermophilic lignocellulosic degradation communities.
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| 50. |
- Vongkampang, Thitiwut, et al.
(författare)
-
Chitosan flocculation associated with biofilms of C. saccharolyticus and C. owensensis enhances biomass retention in a CSTR
- 2021
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Ingår i: International Journal of Hydrogen Energy. - : Elsevier BV. - 1879-3487 .- 0360-3199. ; 46:41, s. 21338-21347
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Tidskriftsartikel (refereegranskat)abstract
- Cell immobilization and co-culture techniques have gained attention due to its potential to obtain high volumetric hydrogen productivities (QH2). Chitosan retained biomass in the fermentation of co-cultures of Caldicellulosiruptor saccharolyticus and C. owensensis efficiently, up to a maximum dilution rate (D) of 0.9 h−1. Without chitosan, wash out of the co-culture occurred earlier, accompanied with approximately 50% drop in QH2 (D > 0.4 h−1). However, butyl rubber did not show as much potential as carrier material; it did neither improve QH2 nor biomass retention in continuous culture. The population dynamics revealed that C. owensensis was the dominant species (95%) in the presence of chitosan, whereas C. saccharolyticus was the predominant (99%) during cultivation without chitosan. In contrast, the co-culture with rubber as carrier maintained the relative population ratios around 1:1. This study highlighted chitosan as an effective potential carrier for immobilization, thereby paving the way for cost – effective hydrogen production.
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