S123: Stability of the high solids fermentation phenotype of isolates from an evolved strain of Saccharomyces cerevisiae

Saccharomyces cerevisiae strain AJP50 was generated by evolving industrial strain XR122N in steam exploded pine wood with the aim of generating a strain that could efficiently ferment high dry matter of pine. Individual colonies were screened for resistance to inhibitors  and for the ability to ferment high concentrations of pretreated pine. Two clonal isolates, GHP1 and GHP4, obtained from the AJP50 population were compared in fermentations of 17.5% dry weight per volume of pretreated pine wood after growth in either rich media (YPD) or rich media supplemented with 13 different inhibitory compounds found in pretreated biomass fermentations (YPDI). After growth in YPDI media both GHP1 and GHP4 were able to consistently and efficiently ferment the biomass to ethanol at nearly the theoretical maximum yield. After growth in YPD media only isolate GHP4 was able to ferment 17.5% dry wt/vol of pine; whereas isolate GHP1 had drastically reduced fermentative performance after growth in YPD. Loss of the high solids fermentation phenotype observed in YPD grown GHP1 was exploited to help determine which genetic features may be important for the fermentation of high biomass concentrations. The transcriptomes of YPD and YPDI grown GHP1 and GHP4 were sequenced and analyzed. Gene expression levels of inocula able to ferment high pine solids (YPDI grown isolates and YPD grown GHP4) were compared to the expression levels observed in inocula unable to ferment high pine solids (YPD grown GHP1) elucidate many factors that may be important for the efficient fermentations of very high solids pretreated biomass.