| 1. |
- Abdelaziz, Omar Y., et al.
(författare)
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Biological valorization of low molecular weight lignin
- 2016
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Ingår i: Biotechnology Advances. - : Elsevier BV. - 0734-9750. ; 34:8, s. 1318-1346
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Forskningsöversikt (refereegranskat)abstract
- Lignin is a major component of lignocellulosic biomass and as such, it is processed in enormous amounts in the pulp and paper industry worldwide. In such industry it mainly serves the purpose of a fuel to provide process steam and electricity, and to a minor extent to provide low grade heat for external purposes. Also from other biorefinery concepts, including 2nd generation ethanol, increasing amounts of lignin will be generated. Other uses for lignin – apart from fuel production – are of increasing interest not least in these new biorefinery concepts. These new uses can broadly be divided into application of the polymer as such, native or modified, or the use of lignin as a feedstock for the production of chemicals. The present review focuses on the latter and in particular the advances in the biological routes for chemicals production from lignin. Such a biological route will likely involve an initial depolymerization, which is followed by biological conversion of the obtained smaller lignin fragments. The conversion can be either a short catalytic conversion into desired chemicals, or a longer metabolic conversion. In this review, we give a brief summary of sources of lignin, methods of depolymerization, biological pathways for conversion of the lignin monomers and the analytical tools necessary for characterizing and evaluating key lignin attributes.
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| 2. |
- Abdelaziz, Omar Y., et al.
(författare)
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Oxidative Depolymerization of Kraft Lignin for Microbial Conversion
- 2019
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Ingår i: ACS Sustainable Chemistry and Engineering. - : American Chemical Society (ACS). - 2168-0485. ; 7:13, s. 11640-11652
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Tidskriftsartikel (refereegranskat)abstract
- The valorization of lignin is being increasingly recognized as crucial to improve the economic viability of integrated biorefineries. Because of its inherent heterogeneity and recalcitrance, lignin has been treated as a waste product in the pulp and paper industry, but new technologies are now being explored to transform lignin into a sustainable resource and enhance its value chain. In the present study, alkaline oxidative depolymerization was investigated as a potential form of pretreatment to enable further biological conversion of LignoBoost kraft lignin (LB). LB lignin oxidation reactions were studied at various temperatures (120-200 °C) and O2 partial pressures (3-15 bar) to identify the optimal conditions for obtaining a biocompatible, oxidatively depolymerized lignin (ODLB) stream. The low molecular weight compounds resulting from this treatment consisted mainly of aromatic monomers and carboxylic acids. The highest yield of aromatic monomers, 3 wt %, was obtained at 160 °C and 3 bar O2. The yield of carboxylic acids increased with both increasing temperature and O2 pressure, exceeding 13% under the harshest conditions investigated. The growth of four aromatic-catabolizing bacterial strains was examined on reaction product mixtures, all of which showed growth on agar plates utilizing ODLB as the sole source of carbon and energy. Rhodococcus opacus and Sphingobium sp. SYK-6 were found to consume most of the aromatic monomers present in the ODLB (e.g., vanillin, vanillate, acetovanillone, and guaiacol). The findings of this study indicate that pretreatment by oxidative depolymerization has potential in the biological valorization of technical lignin streams, for the production of valuable chemicals and materials.
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| 3. |
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| 4. |
- Almqvist, Henrik, et al.
(författare)
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Characterization of the Weimberg Pathway in Caulobacter crescentus
- 2018
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Ingår i: Fermentation. - : MDPI AG. - 2311-5637. ; 4:2
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Tidskriftsartikel (refereegranskat)abstract
- Caulobacter crescentus is a gram-negative bacterium that can utilize xylose as a substrate using the Weimberg pathway, which converts xylose to α-ketoglutarate in five steps without carbon loss. This is an interesting pathway for heterologous expression in other organisms in order to enable xylose utilization in biorefinery processes. C. crescentus was grown on xylose, arabinose and glucose, and maximum specific growth rates determined for the three substrates were 0.11 h−1, 0.05 h−1, and 0.15 h−1 respectively. Growth was found to be significantly inhibited at sugar concentration of 20 g L−1, shown primarily by an increased lag phase. Enzyme activity assays showed that the Weimberg pathway was active in cells grown, not only on xylose but also on arabinose. No activity was found for growth on glucose. Furthermore, substantial amounts of α-ketoglutarate—up to a yield of 0.4 g g−1—was excreted during growth on xylose, but no other extracellular intermediates in the Weimberg pathway were detected during growth on xylose. Apparently, C. crescentus is not well adapted for efficient growth on high xylose levels, and responds by an extended lag phase and secretion of α-ketoglutarate.
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| 5. |
- Almqvist, Henrik, et al.
(författare)
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Succinic acid production by Actinobacillus succinogenes from batch fermentation of mixed sugars
- 2016
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Ingår i: Journal of Industrial Microbiology & Biotechnology. - : Oxford University Press (OUP). - 1367-5435 .- 1476-5535. ; 43:8, s. 1117-1130
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Tidskriftsartikel (refereegranskat)abstract
- Succinic acid production from the monosaccharides xylose, arabinose, glucose, mannose and galactose was studied using the bacterium Actinobacillus succinogenes. In Duran bottle cultures, containing 10 g/L of each of sugar, succinic acid was produced from all sugars except for galactose. The highest succinate yield, 0.56 g/g, was obtained with glucose, whereas the succinate yield was 0.42, 0.38 and 0.44 g/g for xylose, mannose and arabinose, respectively. The specific succinate productivity was 0.7 g/g h for glucose, but below 0.2 g/g h for the other sugars. Batch bioreactor fermentations were carried out using a sugar mixture of the five sugars giving a total concentration of 50 g/L, mimicking the distribution of sugars in spent sulfite liquor (SSL) from Eucalyptus which is rich in xylose. In this mixture, an almost complete conversion of all sugars (except galactose) was achieved resulting in a final succinate concentration of 21.8–26.8 g/L and a total yield of 0.59–0.68 g/g. There was evidence of co-consumption of glucose and xylose, whereas mannose was consumed after glucose. The main by-products were acetate 0.14–0.20 g/g and formate 0.08–0.13 g/g. NADH balance calculations suggested that NADH required for succinate production was not met solely from formate and acetate production, but other means of NADH production was necessary. Results from mixed sugar fermentations were verified using SSL as substrate resulting in a succinate yield of 0.60 g/g. In addition, it was found that CO2 sparging could replace carbonate supply in the form of MgCO3 without affecting the succinate yield.
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| 6. |
- Arkitektur & teknik, Årskurs 2, et al.
(författare)
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På fötter genom England 2016
- 2016
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Denna resedagbok är en del av Arkitektur och teknik-studenternas förberedelse för årskurs 3 och särskilt en träning i att söka, upptäcka och iakkta arkitekturens komplexa sammanhang och de värden som kan skapas genom arkitektur. Under studieresan byggs ett grundmaterial till dagboken upp genom förberedda presentationer, gemensamma analyser, undersökande skisser och konstnärliga övningar. Studieresan följs upp och bearbetas vid seminarier och genom korsläsning av texter där studenterna uppmanas till ett personligt reflekterande hållningssätt. På så sätt blir dagboken ett levande dokument som visar vår glädje och nyfikenhet över de många broar och byggnader vi upplevt tillsammans, och ett dokument som vill locka oss och alla läsare till vidare upptäcktsfärder.
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| 7. |
- Borgström, Celina, et al.
(författare)
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Identification of modifications procuring growth on xylose in recombinant Saccharomyces cerevisiae strains carrying the Weimberg pathway
- 2019
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Ingår i: Metabolic Engineering. - : Elsevier BV. - 1096-7176. ; 55, s. 1-11
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Tidskriftsartikel (refereegranskat)abstract
- The most prevalent xylose-assimilating pathways in recombinant Saccharomyces cerevisiae, i.e. the xylose isomerase (XI) and the xylose reductase/xylitol dehydrogenase (XR/XDH) pathways, channel the carbon flux through the pentose phosphate pathway and further into glycolysis. In contrast, the oxidative and non-phosphorylative bacterial Weimberg pathway channels the xylose carbon through five steps into the metabolic node α-ketoglutarate (αKG) that can be utilized for growth or diverted into production of various metabolites. In the present study, steps preventing the establishment of a functional Weimberg pathway in S. cerevisiae were identified. Using an original design where a S. cerevisiae strain was expressing the essential four genes of the Caulobacter crescentus pathway (xylB, xylD, xylX, xylA) together with a deletion of FRA2 gene to upregulate the iron-sulfur metabolism, it was shown that the C. crescentus αKG semialdehyde dehydrogenase, XylA was not functional in S. cerevisiae. When replaced by the recently described analog from Corynebacterium glutamicum, KsaD, significantly higher in vitro activity was observed but the strain did not grow on xylose. Adaptive laboratory evolution (ALE) on a xylose/glucose medium on this strain led to a loss of XylB, the first step of the Weimberg pathway, suggesting that ALE favored minimizing the inhibiting xylonate accumulation by restricting the upper part of the pathway. Therefore three additional gene copies of the lower Weimberg pathway (XylD, XylX and KsaD) were introduced. The resulting S. cerevisiae strain (ΔΔfra2, xylB, 4x (xylD-xylX-ksaD)) was able to generate biomass from xylose and Weimberg pathway intermediates were detected. To our knowledge this is the first report of a functional complete Weimberg pathway expressed in fungi. When optimized this pathway has the potential to channel xylose towards value-added specialty chemicals such as dicarboxylic acids and diols.
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| 8. |
- Brink, Daniel P., et al.
(författare)
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Mapping the diversity of microbial lignin catabolism : experiences from the eLignin database
- 2019
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 0175-7598 .- 1432-0614. ; , s. 3979-4002
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Forskningsöversikt (refereegranskat)abstract
- Lignin is a heterogeneous aromatic biopolymer and a major constituent of lignocellulosic biomass, such as wood and agricultural residues. Despite the high amount of aromatic carbon present, the severe recalcitrance of the lignin macromolecule makes it difficult to convert into value-added products. In nature, lignin and lignin-derived aromatic compounds are catabolized by a consortia of microbes specialized at breaking down the natural lignin and its constituents. In an attempt to bridge the gap between the fundamental knowledge on microbial lignin catabolism, and the recently emerging field of applied biotechnology for lignin biovalorization, we have developed the eLignin Microbial Database (www.elignindatabase.com), an openly available database that indexes data from the lignin bibliome, such as microorganisms, aromatic substrates, and metabolic pathways. In the present contribution, we introduce the eLignin database, use its dataset to map the reported ecological and biochemical diversity of the lignin microbial niches, and discuss the findings.
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| 9. |
- Carlquist, Magnus, et al.
(författare)
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Process engineering for bioflavour production with metabolically active yeast - a minireview.
- 2015
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Ingår i: Yeast. - 1097-0061. ; 32:1, s. 123-143
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Forskningsöversikt (refereegranskat)abstract
- Flavours are biologically active molecules of large commercial interest in the food, cosmetics, detergent and pharmaceutical industry. The production of flavours can take place by either extraction from plant materials, chemical synthesis, through biological conversion of precursor molecules or through de novo biosynthesis. The latter alternatives are gaining importance through the rapidly growing fields of systems biology and metabolic engineering giving efficient production hosts for the so-called "bioflavours", which are natural flavour and/or fragrance compounds obtained with cell factories or enzymatic systems. One potential production host for bioflavour is yeast. In this mini-review, we give an overview of bioflavour production in yeast from the process engineering perspective. Two specific examples - production of 2-phenylethanol and vanillin - are used to illustrate process challenges and strategies used.
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| 10. |
- Carrasco, Cristhian, et al.
(författare)
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SO2-catalysed steam pretreatment of quinoa stalks
- 2015
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Ingår i: Journal of Chemical Technology and Biotechnology. - : Wiley. - 0268-2575. ; 90:1, s. 64-71
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUNDQuinoa is a pseudo-cereal grown predominantly in South America. The quinoa stalks are lignocellulosic residues, which have a limited use today. The objective of the current study was to assess the potential of this material as a source of monosaccharides for fermentation purposes by means of steam pretreatment giving sugars from the hemicellulose part, and enzymatic hydrolysis of the solid fraction obtained. SO2 catalysed steam pretreatment was carried out with a holding time of 5min at temperatures between 180 and 220 degrees C. The pretreatment was carried out at two different scales, a small reactor of size 0.5L and a somewhat larger reactor of size 10L, to allow comparison of scale effects in the pretreatment. RESULTSThe highest xylose yield in the liquid phase, obtained after pretreatment at 210 degrees C, was 80%. In the smaller scale unit, longer residence times were needed. The enzymatic hydrolysis, at an enzyme loading of 15 FPU g(-1) glucan and a WIS loading of 2%, resulted in a glucose yield of 70% based on the original glucan. The overall sugar yield, including the xylan hydrolysed in the enzymatic treatment, at dilute conditions was 75%. CONCLUSIONSSO2 catalysed pretreatment of quinoa straw followed by enzymatic hydrolysis gave a relatively good sugar yield. However, the yield obtained was somewhat lower than previously reported for similar materials, such as wheat straw and sugarcane bagasse, steam pretreated with SO2. (c) 2013 Society of Chemical Industry
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