title: Phenotypic selection of a wild Saccharomyces cerevisiae strain for simultaneous saccharification and co-fermentation of AFEX™ pretreated corn stover.
abstract: BACKGROUND
  Simultaneous saccharification and co-fermentation (SSCF) process involves enzymatic hydrolysis of pretreated lignocellulosic biomass and fermentation of glucose and xylose in one bioreactor. The optimal temperatures for enzymatic hydrolysis are higher than the standard fermentation temperature of ethanologenic Saccharomyces cerevisiae. Moreover, degradation products resulting from biomass pretreatment impair fermentation of sugars, especially xylose, and can synergize with high temperature stress. One approach to resolve both concerns is to utilize a strain background with innate tolerance to both elevated temperatures and degradation products.
  
  
  RESULTS
  In this study, we screened a panel of 108 wild and domesticated Saccharomyces cerevisiae strains isolated from a wide range of environmental niches. One wild strain was selected based on its growth tolerance to simultaneous elevated temperature and AFEX™ (Ammonia Fiber Expansion) degradation products. After engineering the strain with two copies of the Scheffersomyces stipitis xylose reductase, xylitol dehydrogenase and xylulokinase genes, we compared the ability of this engineered strain to the benchmark 424A(LNH-ST) strain in ethanol production and xylose fermentation in standard lab medium and AFEX pretreated corn stover (ACS) hydrolysates, as well as in SSCF of ACS at different temperatures. In SSCF of 9% (w/w) glucan loading ACS at 35°C, the engineered strain showed higher cell viabilities and produced a similar amount of ethanol (51.3 g/L) compared to the benchmark 424A(LNH-ST) strain.
  
  
  CONCLUSIONS
  These results validate our approach in the selection of wild Saccharomyces cerevisiae strains with thermo-tolerance and degradation products tolerance properties for lignocellulosic biofuel production. The wild and domesticated yeast strains phenotyped in this work are publically available for others to use as genetic backgrounds for fermentation of their pretreated biomass at elevated temperatures.
authors.affiliation: Biomass Conversion Research Laboratory (BCRL), Department of Chemical Engineering and Materials Science, Michigan State University, 3900 Collins Road, Lansing, MI 48910, USA ; DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Mingjie
authors.initials: M
authors.lastname: Jin
authors.affiliation: Biomass Conversion Research Laboratory (BCRL), Department of Chemical Engineering and Materials Science, Michigan State University, 3900 Collins Road, Lansing, MI 48910, USA ; DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Cory
authors.initials: C
authors.lastname: Sarks
authors.affiliation: Biomass Conversion Research Laboratory (BCRL), Department of Chemical Engineering and Materials Science, Michigan State University, 3900 Collins Road, Lansing, MI 48910, USA ; DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Christa
authors.initials: C
authors.lastname: Gunawan
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, 1552 University Ave, Madison, WI 53726, USA.
authors.forename: Benjamin D
authors.initials: BD
authors.lastname: Bice
authors.affiliation: Department of Bacteriology, University of Wisconsin-Madison, 1550 Linden Dr, Madison, WI 53706, USA.
authors.forename: Shane P
authors.initials: SP
authors.lastname: Simonett
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, 1552 University Ave, Madison, WI 53726, USA.
authors.forename: Ragothaman
authors.initials: R
authors.lastname: Avanasi Narasimhan
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, 1552 University Ave, Madison, WI 53726, USA ; Department of Bacteriology, University of Wisconsin-Madison, 1550 Linden Dr, Madison, WI 53706, USA ; U.S. Department of Agriculture, Forest Products Laboratory, 1 Gifford Pinchot Dr, Madison, WI 53726, USA.
authors.forename: Laura B
authors.initials: LB
authors.lastname: Willis
authors.affiliation: Biomass Conversion Research Laboratory (BCRL), Department of Chemical Engineering and Materials Science, Michigan State University, 3900 Collins Road, Lansing, MI 48910, USA ; DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Dale
authors.affiliation: Biomass Conversion Research Laboratory (BCRL), Department of Chemical Engineering and Materials Science, Michigan State University, 3900 Collins Road, Lansing, MI 48910, USA ; DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824, USA.
authors.forename: Venkatesh
authors.initials: V
authors.lastname: Balan
authors.affiliation: DOE Great Lakes Bioenergy Research Center, University of Wisconsin-Madison, 1552 University Ave, Madison, WI 53726, USA.
authors.forename: Trey K
authors.initials: TK
authors.lastname: Sato
keywords: AFEX; Degradation products; Ethanol; S. cerevisiae; SSCF; Thermo-tolerance; Xylose fermentation
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