| 1. |
- Mukherjee, Vaskar, 1986, et al.
(författare)
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High throughput screening of yeast strains for desirable stress tolerant traits for bioethanol production
- 2013
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Ingår i: Yeast. - : Wiley. - 0749-503X.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Implementation of very high gravity (VHG) fermentation technology in second generation bioethanol production using raw lignocellulosic biomass is fundamental to establish a commercially viable plant. However, so far the application of this technology is greatly restricted by the unavailability of a fermentative microorganism, resistant enough to the wide variety of stressors commonly encountered in VHG fermentation. In addition, the appropriate tools and knowledge to select such multi-stress tolerant microorganisms and to make a scientifically proven choice of the appropriate candidate strains have been lacking until recently. In this study we screened a large yeast culture collection, consisting of about 700 Saccharomyces cerevisiae and non-Saccharomyces strains from diverse origins, for different desirable traits for bioethanol production. These included, for example, osmotolerance, halotolerance, ethanol tolerance, thermotolerance, and tolerance against fermentation inhibitors like furfural and hydroxymethyl furfural as well as some heavy metals. To this end, a high throughput semi-automated robot was used for spotting up to 96 strains per screening plate. After incubation, plates were scanned and growth was recorded and analyzed using dedicated software. Cluster analysis showed clear differences in tolerance among species and among strains of the same species. In addition, strains showing co-tolerance against different traits could be identified. As such, our study enabled to efficiently select top candidate strains having desirable traits for VHG bioethanol production.
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| 2. |
- Mukherjee, Vaskar, 1986, et al.
(författare)
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Phenotypic evaluation of natural and industrial Saccharomyces yeasts for different traits desirable in industrial bioethanol production
- 2014
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Ingår i: Applied Microbiology and Biotechnology. - : Springer Science and Business Media LLC. - 1432-0614 .- 0175-7598. ; 98:9483
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Tidskriftsartikel (refereegranskat)abstract
- Saccharomyces cerevisiae is the organism of choice for many food and beverage fermentations because it thrives in high-sugar and high-ethanol conditions. However, the conditions encountered in bioethanol fermentation pose specific challenges, including extremely high sugar and ethanol concentrations, high temperature, and the presence of specific toxic compounds. It is generally considered that exploring the natural biodiversity of Saccharomyces strains may be an interesting route to find superior bioethanol strains and may also improve our understanding of the challenges faced by yeast cells during bioethanol fermentation. In this study, we phenotypically evaluated a large collection of diverse Saccharomyces strains on six selective traits relevant for bioethanol production with increasing stress intensity. Our results demonstrate a remarkably large phenotypic diversity among different Saccharomyces species and among S. cerevisiae strains from different origins. Currently applied bioethanol strains showed a high tolerance to many of these relevant traits, but several other natural and industrial S. cerevisiae strains outcompeted the bioethanol strains for specific traits. These multitolerant strains performed well in fermentation experiments mimicking industrial bioethanol production. Together, our results illustrate the potential of phenotyping the natural biodiversity of yeasts to find superior industrial strains that may be used in bioethanol production or can be used as a basis for further strain improvement through genetic engineering, experimental evolution, or breeding. Additionally, our study provides a basis for new insights into the relationships between tolerance to different stressors.
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| 3. |
- Ruyters, Stefan, et al.
(författare)
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Assessing the potential of wild yeasts for bioethanol production
- 2015
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Ingår i: Journal of Industrial Microbiology and Biotechnology. - : Oxford University Press (OUP). - 1367-5435 .- 1476-5535. ; 42:1, s. 39-48
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Tidskriftsartikel (refereegranskat)abstract
- Bioethanol fermentations expose yeasts to a new, complex and challenging fermentation medium with specific inhibitors and sugar mixtures depending on the type of carbon source. It is, therefore, suggested that the natural diversity of yeasts should be further exploited in order to find yeasts with good ethanol yield in stressed fermentation media. In this study, we screened more than 50 yeast isolates of which we selected five isolates with promising features. The species Candida bombi, Wickerhamomyces anomalus and Torulaspora delbrueckii showed better osmo- and hydroxymethylfurfural tolerance than Saccharomyces cerevisiae. However, S. cerevisiae isolates had the highest ethanol yield in fermentation experiments mimicking high gravity fermentations (25 % glucose) and artificial lignocellulose hydrolysates (with a myriad of inhibitors). Interestingly, among two tested S. cerevisiaestrains, a wild strain isolated from an oak tree performed better than Ethanol Red, a S. cerevisiae strain which is currently commonly used in industrial bioethanol fermentations. Additionally, a W. anomalus strain isolated from sugar beet thick juice was found to have a comparable ethanol yield, but needed longer fermentation time. Other non-Saccharomycesyeasts yielded lower ethanol amounts.
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