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

Authors: Mertens, Jeffrey; Skory, Christopher - Chris; Nichols, Nancy; Hector, Ronald - Ron

Submitted to: Biotechnology Progress
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/16/2020
Publication Date: 10/21/2020
Citation: Mertens, J.A., Skory, C.D., Nichols, N.N., Hector, R.E. 2020. Impact of stress-response related transcription factor overexpression on lignocellulosic inhibitor tolerance of Saccharomyces cerevisiae environmental isolates. Biotechnology Progress. 37(2). Article e3094. https://doi.org/10.1002/btpr.3094.
DOI: https://doi.org/10.1002/btpr.3094

Interpretive Summary: Sustainable production of fuels and specialty chemicals will require the use of simple sugars obtained from agricultural biomass. To obtain the simple sugars locked within the agricultural residues, the biomass is broken down by chemical pre-treatments and enzymes. Unfortunately, the chemical pre-treatment processes lead to the formation of inhibitors that are detrimental to potential production organisms such as Saccharomyces cerevisiae, the preferred production host. A great deal of effort has been put forth to eliminate the impact of these inhibitors through process and biocatalyst improvements. Thus far none of these solutions has fully eliminated the problems associated with inhibitors. In this work, transcription factors, proteins that turn on other genes, were expressed at higher levels than normal in three different S. cerevisiae environmental isolates. Increased expression of these stress-response transcription factors in laboratory strains led to improved growth characteristics. However, in more robust S. cerevisiae strains, over expression had no impact and in some cases was detrimental to growth. This finding suggests that overall genetic background also plays a key role in lignocellulosic inhibitor tolerance in S. cerevisiae. This work contributes foundational knowledge supporting development of second generation biocatalysts for producing fuels and chemicals from plant biomass.

Technical Abstract: 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.