title: Evolved strains of Scheffersomyces stipitis achieving high ethanol productivity on acid- and base-pretreated biomass hydrolyzate at high solids loading.
abstract: BACKGROUND
  Lignocellulosic biomass is an abundant, renewable feedstock useful for the production of fuel-grade ethanol via the processing steps of pretreatment, enzyme hydrolysis, and microbial fermentation. Traditional industrial yeasts do not ferment xylose and are not able to grow, survive, or ferment in concentrated hydrolyzates that contain enough sugar to support economical ethanol recovery since they are laden with toxic byproducts generated during pretreatment.
  
  
  RESULTS
  Repetitive culturing in two types of concentrated hydrolyzates was applied along with ethanol-challenged xylose-fed continuous culture to force targeted evolution of the native pentose fermenting yeast Scheffersomyces (Pichia) stipitis strain NRRL Y-7124 maintained in the ARS Culture Collection, Peoria, IL. Isolates collected from various enriched populations were screened and ranked based on relative xylose uptake rate and ethanol yield. Ranking on hydrolyzates with and without nutritional supplementation was used to identify those isolates with best performance across diverse conditions.
  
  
  CONCLUSIONS
  Robust S. stipitis strains adapted to perform very well in enzyme hydrolyzates of high solids loading ammonia fiber expansion-pretreated corn stover (18% weight per volume solids) and dilute sulfuric acid-pretreated switchgrass (20% w/v solids) were obtained. Improved features include reduced initial lag phase preceding growth, significantly enhanced fermentation rates, improved ethanol tolerance and yield, reduced diauxic lag during glucose-xylose transition, and ability to accumulate >40 g/L ethanol in <167 h when fermenting hydrolyzate at low initial cell density of 0.5 absorbance units and pH 5 to 6.
authors: Bioenergy Research Unit, National Center for Agricultural Utilization Research, USDA-ARS, 1815 N. University, Peoria, IL 61604 USA.
authors: Patricia J
authors: PJ
authors: Slininger
authors: Bioenergy Research Unit, National Center for Agricultural Utilization Research, USDA-ARS, 1815 N. University, Peoria, IL 61604 USA.
authors: Maureen A
authors: MA
authors: Shea-Andersh
authors: Bioenergy Research Unit, National Center for Agricultural Utilization Research, USDA-ARS, 1815 N. University, Peoria, IL 61604 USA.
authors: Stephanie R
authors: SR
authors: Thompson
authors: Bioenergy Research Unit, National Center for Agricultural Utilization Research, USDA-ARS, 1815 N. University, Peoria, IL 61604 USA.
authors: Bruce S
authors: BS
authors: Dien
authors: Bacterial Foodborne Pathogens and Mycology Research, National Center for Agricultural Utilization Research, USDA-ARS, 1815 N. University, Peoria, IL 61604 USA.
authors: Cletus P
authors: CP
authors: Kurtzman
authors: DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824 USA.
authors: Venkatesh
authors: V
authors: Balan
authors: DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824 USA.
authors: Leonardo
authors: L
authors: da Costa Sousa
authors: DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824 USA.
authors: Nirmal
authors: N
authors: Uppugundla
authors: DOE Great Lakes Bioenergy Research Center, Michigan State University, East Lansing, MI 48824 USA.
authors: Bruce E
authors: BE
authors: Dale
authors: Bioenergy Research Unit, National Center for Agricultural Utilization Research, USDA-ARS, 1815 N. University, Peoria, IL 61604 USA.
authors: Michael A
authors: MA
authors: Cotta
keywords: Adaptation; Biofuel; Fermentation; Lignocellulose; Pichia stipitis; Yeast