Impact of stress-response related transcription factor overexpression on lignocellulosic inhibitor tolerance of Saccharomyces cerevisiae environmental isolates.

Numerous transcription factor genes associated with stress response are upregulated in Saccharomyces cerevisiae grown in the presence of inhibitors that result from pretreatment processes to unlock simple sugars from biomass. To determine if overexpression of transcription factors could improve inhibitor tolerance in robust S. cerevisiae environmental isolates as has been demonstrated in S. cerevisiae haploid laboratory strains, transcription factors were overexpressed at three different expression levels in three S. cerevisiae environmental isolates. Overexpression of the YAP1 transcription factor in these isolates did not lead to increased growth rate or reduced lag in growth, and in some cases was detrimental, when grown in the presence of either lignocellulosic hydrolysates or furfural and 5-hydroxymethyl furfural individually. The expressed Yap1p localized correctly and the expression construct improved inhibitor tolerance of a laboratory strain as previously reported, indicating that lack of improvement in the environmental isolates was due to factors other than nonfunctional expression constructs or mis-folded protein. Additional stress-related transcription factors, MSN2, MSN4, HSF1, PDR1, and RPN4, were also overexpressed at three different expression levels and all failed to improve inhibitor tolerance. Transcription factor overexpression alone is unlikely to be a viable route toward increased inhibitor tolerance of robust environmental S. cerevisiae strains.