| 1. |
- Moreno, David, 1986, et al.
(författare)
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An engineered Saccharomyces cerevisiae for cost-effective lignocellulosic bioethanol production: process performance and physiological insights
- 2015
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Ingår i: 37th Symposium on Biotechnology for Fuels and Chemicals.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The success in the commercialization of lignocellulosic bioethanol relies on the development of microorganisms with efficient hexose and pentose fermentation and tolerance towards inhibitory by-products (acetic acid, furan aldehydes and phenolics) generated during biomass processing. Traditionally, the yeast Saccharomyces cerevisiae is the preferred microorganism for industrial ethanol production. Many years of research and development have been conducted to develop S. cerevisiae strains suitable for fermenting lignocellulosic-based streams. S. cerevisiae is robust and ferment glucose efficiently, but it has been proved to be difficult to genetically modify for efficient xylose fermentation. In this work, a xylose-fermenting S. cerevisiae strain was subjected to evolutionary engineering, boosting its robustness and xylose fermentation capacity. The evolved strain was able to ferment a non-diluted enzymatic hydrolysate (representing 23% (w/w) dry matter of steam-exploded wheat straw), reaching ethanol titers higher than 5% (w/w) after 48 h. Within the first 24 h, glucose and xylose were co-consumed with rates of 3.1 and 0.7 g/L h, respectively, and converted to ethanol with yields corresponding to 93% of the theoretical. In addition, once glucose was depleted, xylose was consumed with a similar rate until reducing 70% of its initial concentration (36 h after inoculation). Besides investigating the fermentation parameters, the differences in gene expression levels and enzymatic activities of xylose-assimilating pathway were analyzed. These analyses will be the foundation for understanding the improved phenotype and the physiological mechanisms for efficient xylose fermentation, after which potential targets for subsequent metabolic engineering may be identified.
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| 2. |
- Franzén, Carl Johan, 1966, et al.
(författare)
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Multifeed simultaneous saccharification and fermentation enables high gravity submerged fermentation of lignocellulose.
- 2015
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Ingår i: Recent Advances in Fermentation Technology (RAFT 11), Clearwater Beach, Florida, USA, November 8-11, 2015. Oral presentation..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Today, second generation bioethanol production is becoming established in production plants across the world. In addition to its intrinsic value, the process can be viewed as a model process for biotechnological conversion of recalcitrant lignocellulosic raw materials to a range of chemicals and other products. So called High Gravity operation, i.e. fermentation at high solids loadings, represents continued development of the process towards higher product concentrations and productivities, and improved energy and water economy. We have employed a systematic, model-driven approach to the design of feeding schemes of solid substrate, active yeast adapted to the actual substrate, and enzymes to fed-batch simultaneous saccharification and co-fermentation (Multifeed SSCF) of steam-pretreated lignocellulosic materials in stirred tank reactors. With this approach, mixing problems were avoided even at water insoluble solids contents of 22%, leading to ethanol concentrations of 56 g/L within 72 hours of SSCF on wheat straw. Similar fermentation performance was verified in 10 m3 demonstration scale using wheat straw, and in lab scale on birch and spruce, using several yeast strains. The yeast was propagated in the liquid fraction obtained by press filtration of the pretreated slurry. Yet, even with such preadaptation and repeated addition of fresh cells, the viability in the SSCF dropped due to interactions between lignocellulose-derived inhibitors, the produced ethanol and the temperature. Decreasing the temperature from 35 to 30°C when the ethanol concentration reached 40-50 g/L resulted in rapid initial hydrolysis, maintained fermentation capacity, lower residual glucose and xylose and ethanol concentrations above 60 g/L.
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| 3. |
- Moreno, A. D., et al.
(författare)
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A review of biological delignification and detoxification methods for lignocellulosic bioethanol production
- 2015
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Ingår i: Critical Reviews in Biotechnology. - : Informa UK Limited. - 0738-8551 .- 1549-7801. ; 35:3, s. 342-354
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Forskningsöversikt (refereegranskat)abstract
- Future biorefineries will integrate biomass conversion processes to produce fuels, power, heat and value-added chemicals. Due to its low price and wide distribution, lignocellulosic biomass is expected to play an important role toward this goal. Regarding renewable biofuel production, bioethanol from lignocellulosic feedstocks is considered the most feasible option for fossil fuels replacement since these raw materials do not compete with food or feed crops. In the overall process, lignin, the natural barrier of the lignocellulosic biomass, represents an important limiting factor in biomass digestibility. In order to reduce the recalcitrant structure of lignocellulose, biological pretreatments have been promoted as sustainable and environmentally friendly alternatives to traditional physico-chemical technologies, which are expensive and pollute the environment. These approaches include the use of diverse white-rot fungi and/or ligninolytic enzymes, which disrupt lignin polymers and facilitate the bioconversion of the sugar fraction into ethanol. As there is still no suitable biological pretreatment technology ready to scale up in an industrial context, white-rot fungi and/or ligninolytic enzymes have also been proposed to overcome, in a separated or in situ biodetoxification step, the effect of the inhibitors produced by non-biological pretreatments. The present work reviews the latest studies regarding the application of different microorganisms or enzymes as useful and environmentally friendly delignification and detoxification technologies for lignocellulosic biofuel production. This review also points out the main challenges and possible ways to make these technologies a reality for the bioethanol industry.
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| 4. |
- Moreno, David, 1986, et al.
(författare)
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Exploring laccase and mediators behavior during saccharification and fermentation of steam-exploded wheat straw for bioethanol production
- 2016
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Ingår i: Journal of Chemical Technology and Biotechnology. - : Wiley. - 1097-4660 .- 0268-2575. ; 91:6, s. 1816-1825
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: Laccases represent a very powerful tool to improve biorefining processes from lignocellulosic feedstocks. These enzymes are being investigated not only for potential use as pretreatment agents in bioethanol production, mainly as a delignifying agent, but also as a biotechnological tool for removal of inhibitors (mainly phenols) of subsequent fermentation processes. RESULTS: In this work, the treatment of the water insoluble solids (WIS) fraction from steam-exploded wheat straw with Pycnoporus cinnabarinus laccase and different laccase-mediator systems (LMS) did not decrease the lignin content, resulting in lower glucose recoveries during the subsequent saccharification. In combination with an alkaline extraction, the treatment with laccase/LMS produced no synergistic effect enhancing the delignification or saccharification of WIS. In contrast, laccase reduced the soluble phenols (95% of the total phenols identified) of the whole slurry from steam-exploded wheat straw, improving the yeast performance during the fermentation and enhancing the ethanol yields. CONCLUSIONS: The efficiency of P. cinnabarinus laccase with or without mediators as a delignifying agent on steam-exploded wheat straw for bioethanol production was not observed, whereas its detoxification ability was shown. Thus, new laccases or designing laccases with ability to delignify and detoxify simultaneously needs to be explored in order to produce major ethanol global yields.
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| 5. |
- Tomas-Pejo, Elia, 1980, et al.
(författare)
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Heads and tails of laccases in bioethanol production
- 2015
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Ingår i: 37th Symposium on Biotechnology for Fuels and Chemicals.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- In a lignocellulosic biorefinery, the sugar platform could lead to bioethanol production through biochemical routes. The bioethanol production process is, however, hindered by the recalcitrant structure of lignocellulose and a pretreatment is needed to increase biomass digestibility. Current pretreatment technologies generate inhibitory compounds that hamper the sugar conversion to ethanol by the fermenting microorganism.High ethanol titers are necessary to make the process economically-viable. This could be reached by using high substrate loadings, which implies high inhibitor concentration in the broth. Laccases are powerful biocatalysts to overcome the effect of inhibitory compounds. Laccases are multicopper oxidases that catalyze the oxidation of substituted phenols, anilines and aromatic thiols to their corresponding radicals. This capacity allows laccases to act specifically on phenolic compounds present in pretreated materials.In our studies, the potential of laccases as detoxification agents has been demonstrated by removing 70 to 100% of total phenols. Laccases trigger the fermentation of slurries non-fermentable without laccase treatment by increasing dramatically the ethanol yield (from 0.1 g/g to 0.36 g/g). The implementation of the laccase detoxification step boosts ethanol production at substrate loadings as high as 25% (w/w) reaching 58.6 g/L ethanol concentration for a cost-effective industrial ethanol production.Despite the great phenolic reduction, sugar recovery is reduced after laccase addition. Our results suggest that laccase-derived products exert a negative effect on enzymatic hydrolysis. An increase in Klason lignin together with changes observed in the ATR–FTIR spectra supported a grafting process that would limit the accessibility of cellulolytic enzymes to cellulose.
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| 6. |
- Tomas-Pejo, Elia, 1980, et al.
(författare)
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Influence of the propagation strategy for obtaining robust Saccharomyces cerevisiae cells that efficiently co-ferment xylose and glucose in lignocellulosic hydrolysates
- 2015
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Ingår i: Microbial Biotechnology. - : Wiley. - 1751-7907 .- 1751-7915. ; 8:6, s. 999-1005
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Tidskriftsartikel (refereegranskat)abstract
- Development of xylose-fermenting yeast strains that are tolerant to the inhibitors present in lignocellulosic hydrolysates is crucial to achieve efficient bioethanol production processes. In this study, the importance of the propagation strategy for obtaining robust cells was studied. Addition of hydrolysate during propagation of the cells adapted them to the inhibitors, resulting in more tolerant cells with shorter lag phases and higher specific growth rates in minimal medium containing acetic acid and vanillin than unadapted cells. Addition of hydrolysate during propagation also resulted in cells with better fermentation capabilities. Cells propagated without hydrolysate were unable to consume xylose in wheat straw hydrolysate fermentations, whereas 40.3% and 97.7% of the xylose was consumed when 12% and 23% (v/v) hydrolysate, respectively, was added during propagation. Quantitative polymerase chain reaction revealed changes in gene expression, depending on the concentration of hydrolysate added during propagation. This study highlights the importance of using an appropriate propagation strategy for the optimum performance of yeast in fermentation of lignocellulosic hydrolysates. Addition of hydrolysate during propagation of the cells adapted them to the inhibitors, resulting in more tolerant cells with shorter lag phases and higher specific growth rates in minimal medium containing acetic acid and vanillin than unadapted cells. Addition of hydrolysate during propagation also resulted in cells with better fermentation capabilities. This study highlights the importance of using an appropriate propagation strategy for the optimum performance of yeast in fermentation of lignocellulosic hydrolysates.
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