8-21: Isolates of Saccharomyces cerevisiae AJP50, an evolved yeast population, retain the ability to ferment high concentrations of pine wood and resist the effects of inhibitory compounds

Saccharomyces cerevisiae yeast strain AJP50 was evolved to better ferment pretreated pine wood to ethanol and fermented 17.5% dry weight/vol (dwt/v) of SO₂ pretreated pine wood in our previously reported studies. Colonies isolated from AJP50 retained their ability to grow in media containing inhibitory compounds commonly found in pretreated lignocellulosic biomass, and they retained this ability even after subculturing. In the current study, isolated colonies were obtained from the original AJP50 population and screened for their ability to grow in media that contained inhibitory compounds and to ferment high concentrations of pretreated pine as well. Four individual isolates were selected for further study and all retained the ability to ferment 17.5% dwt/v of pine when cultured for 24 hours in yeast peptone dextrose (YPD) media that was supplemented with 13 different inhibitory compounds. However, two of the isolates (GHP1 and GHP2) were unable to produce more than 5% of the theoretical maximum of ethanol when grown in YPD without inhibitors; whereas the other two isolates (GHP3 and GHP4) were still able to produce an equivalent ethanol yield. All four isolates are able to ferment 20% dry weight of purified cellulose (Sigmacell), used to simulate high solids fermentation without inhibitory compounds. All four isolates display similar growth phenotypes in model fermentation media. These data suggests that isolates GHP3 and GHP4 are phenotypically distinct from isolates GHP1 and GHP2.  GHP1 and GHP4 were selected for proteomic and transcriptomic study to elucidate the mechanism behind our observed phenotypes.