| 1. |
- Tomas-Pejo, Elia, 1980, et al.
(författare)
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Effect of inhibitors present n lignocellulosic hydrolysates on evolved xylose fermenting Saccharomyces cerevisiae strains
- 2012
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Ingår i: 34th Symposium for Biofuels and Chemicals. New Orleans, USA. 30th April – 3rd May 2012.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The development of inhibitor tolerant ethanologenic yeasts is one of the important challenges for a successful bioethanol production process from lignocellulose. Furthermore, an efficient microorganism for bioethanol production has to be able to ferment xylose together with glucose since xylose represents a large fraction in the lignocellulosic biomass. Weak acids and phenolic compounds are some of the prevalent inhibitors generated during pretreatment of lignocellulose and they will be present in the fermentation broth stressing the yeast affecting the fermentation performance. Although some studies on the effect of organic acids on fermenting microorganisms have been published, there is a lack of knowledge on the effect of phenolic compounds on yeast and more concretely about the effect on the xylose fermentation performance. In this study, the effect of acetic acid and vanillin on yeast growth on glucose and xylose will be elucidated using synthetic media mimicking lignocellulosic hydrolysates. It is known that one of general stress responses in yeast is the accumulation and mobilization of energy reserves (trehalose and glycogen). Trehalose protects cells from damage, increasing cell viability, however, when inhibitors are present in the media the trehalose synthesis and degradation could be affected. Furthermore differences in gene expression of key genes involved in acetic acid and vanillin tolerance and xylose fermentation will be studied. In this work we will also compare different evolved strains and evaluate mixed populations compared to single clones, in terms of trehalose and glycogen content and inhibitor tolerance.
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| 2. |
- Moreno, David, 1986, et al.
(författare)
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Increasing the tolerance of the non-conventional yeast Candida intermedia to ethanol and lignocellulose-derived inhibitors
- 2016
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Ingår i: 4th Symposium on Biotechnology Applied to Lignocelluloses.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The necessity of providing ‘robust microorganisms’ – defined as the ability to efficiently ferment all the available sugars (both hexoses and pentoses) and to cope with the main stressors present during the fermentation process (including biomass-derived products and ethanol) – represents one of the major challenges for a cost-effective lignocellulosic bioethanol production. The yeast Saccharomyces cerevisiae is the preferred fermentative microorganism in the current bioethanol industry due to its superior fermentation capacity of hexose sugars and its tolerance to several inhibitory compounds. The main disadvantage of S. cerevisiae is, however, its inability to ferment xylose, the second most abundant sugar in lignocellulose (>30% of the total sugar). Metabolic and evolutionary engineering methods have been applied to allow xylose fermentation in S. cerevisiae. Still, xylose-fermenting S. cerevisiae strains lack an efficient xylose-to-ethanol conversion system and issues such as low xylose uptake rates and conversion yields, redox imbalance and the lack of simultaneous use of glucose and xylose are important parameters that still need to be optimized. As an alternative to genetically modified S. cerevisiae strains, non-conventional, native xylose-utilizing yeasts such as the Scheffersomyces species S. stipitis and S. shehatae, Spathaspora passalidarum and various Candida species (C. tropicalis, C. guilliermondii or C. intermedia) have been considered for the fermentation of pentose sugars. These yeasts have, however, a modest tolerance to lignocellulose-derived inhibitors and ethanol, which limits their applicability. Candida intermedia is a xylose-fermenting yeast species that encompasses a high capacity xylose transport system. This trait makes C. intermedia attractive for being a non-GMO alternative in the lignocellulosic bioethanol industry. In the present work, the ethanol tolerance and the fermentation capacity in the presence of lignocellulose-derived inhibitors of an in-house isolated C. intermedia strain was evaluated. The isolated strain showed a medium-tolerance towards lignocellulose-derived inhibitors, being more sensitive when using xylose as a carbon source. The ethanol concentration above which there is no growth was estimated to be 42 g/L when growing in glucose and 55 g/L when growing in xylose. The isolated strain was subjected to evolutionary engineering with the aim of increasing its tolerance towards both lignocellulose-derived inhibitors and ethanol. The obtained evolved population was able to ferment a lignocellulosic hydrolysate (steam-exploded wheat straw), not fermentable by the isolated strain. Furthermore, the evolved population produced higher biomass concentration (7.5-fold higher OD600nm values) when growing in the presence of 36 g/L ethanol, compared to the parental strain. These results highlight the potential of C. intermedia to become a robust yeast microorganism for the lignocellulose-to-ethanol conversion.
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| 3. |
- Muzamal, Muhammad, 1986, et al.
(författare)
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Contribution of Structural Modification to Enhanced Enzymatic Hydrolysis and 3-D Structural Analysis of Steam-Exploded Wood using X-Ray Tomography
- 2016
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Ingår i: BioResources. - : BioResources. - 1930-2126 .- 1930-2126. ; 11:4, s. 8509-8521
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Tidskriftsartikel (refereegranskat)abstract
- Steam explosion pretreatment modifies both the chemical and physical structures of a biomass. Chemical modifications are generated during the treatment of biomass with steam at high temperature. Physical modifications are created during the explosion step, which produces disintegrated and defibrillated biomass. In this study, the contribution of each modification to an increase in enzymatic hydrolysis has been studied. It was found that both physical and chemical modifications contributed to an increase in enzymatic hydrolysability. Additionally, high resolution X-ray tomography was performed to identify the structural modification created during the steam explosion process. Comparison of the 3-D microstructure of a steam-exploded wood sample with an untreated wood sample revealed that several kinds of cracks were created during the explosion step, and the micro-structure of the wood sample was vigorously destroyed.
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| 4. |
- Olsson, Lisbeth, 1963, et al.
(författare)
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Jäst skogsavfall blir nylon
- 2017
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Ingår i: Kemivärlden Biotech med Kemisk tidskrift. ; :Nr 4 Juni 2017, s. 15-16
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 5. |
- Xafenias, Nikolaos, 1981, et al.
(författare)
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Evaluating methane and acetate production in microbial electrolysis cells: reactor performance and microbial diversity
- 2013
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Ingår i: Proceedings of the Fifth European Fuel Cell Technology & Applications Conference- Piero Lunghi Conference, 11-13 December 2013, Rome, Italy.
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Konferensbidrag (refereegranskat)abstract
- The work investigated the potential of microbial electrolysis cells (MECs) for methane and acetate production from synthetic wastewater. In a single-chamber MEC operating with acetate as the electron and carbon source, methane and hydrogen were the main reduction products. Acetate consumption as Chemical Oxygen Demand (COD) was 0.26 Kg-COD m-3 d-1, compared to only 0.04 Kg-COD m-3 d-1 in the open circuit control which did not produce considerable biogas amounts. In a similar reactor separated with a cation exchange membrane, acetate could be retrieved from the cathode with an efficiency of up to 85% and rates of 2.5 mM d-1. Phylogenetic analysis revealed that the initial microbial population was enriched with substantially different bacterial species on the two electrodes of each MEC, despite the fact that the electrodes were hydraulically connected. Distinct tasks were carried out by these different microbes, as also supported by the cyclic voltammograms.
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| 6. |
- Xafenias, Nikolaos, 1981, et al.
(författare)
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Exploring the capabilities of microbial electrosynthesis during treatment of low-strength wastewater
- 2013
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Ingår i: Proceedings of the Fourth International Microbial Fuel Cells Conference, 1-4 September 2013, Cairns, Australia.
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Konferensbidrag (refereegranskat)abstract
- Acetate was produced in the biocathode of a dual-chamber reactor at ambient temperatures (21 oC), with the concurrent treatment of low-strength synthetic wastewater in the anode. Cyclic voltammograms (CVs) showed considerable differences between the different electrode conditions and revealed redox peaks that could be proved beneficial during the microbial electrosynthesis of commodity chemicals.
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| 7. |
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