Screening for inhibitor tolerant Saccharomyces cerevisiae strains from diverse environments for use as platform strains for production of fuels and chemicals from biomass

Authors: Mertens, Jeffrey; KELLY, AMY - Monsato Seed Company; Hector, Ronald - Ron

Submitted to: Bioresource Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2018
Publication Date: 9/1/2018
Citation: Mertens, J.A., Kelly, A., Hector, R.E. 2018. Screening for inhibitor tolerant Saccharomyces cerevisiae strains from diverse environments for use as platform strains for production of fuels and chemicals from biomass. Bioresource Technology. 3:154-161. https://doi.org/10.1016/j.biteb.2018.07.006.
DOI: https://doi.org/10.1016/j.biteb.2018.07.006

Interpretive Summary: Renewable means of producing fuels and specialty chemicals will require the use of agricultural biomass. To be used efficiently for these processes, agricultural biomass needs to be broken down by chemical pre-treatments and enzymes into simple sugars. Unfortunately, the chemical pretreatment processes lead to the formation of inhibitors that are detrimental to potential production organisms. A great deal of effort has been put forth to eliminate the impact of these inhibitors through process solutions and engineering of organisms. None of these solutions has thus far eliminated the problems associated with inhibitors. In this work, a screen was designed to find strains of the yeast Saccharomyces cerevisiae, the preferred production organism, with greater natural tolerance to these inhibitors. The yeast strains with greater natural inhibitor tolerance isolated in this work can serve as a platform for further improvements in tolerance and productivity leading to efficient and cost-effective production of fuels and chemical using agricultural biomass.

Technical Abstract: To enable the use of lignocellulosic biomass for the production of fuel or chemicals, biocatalysts need to be isolated or developed to overcome the inhibitors formed during biomass pretreatment processes to release simple sugars. In this work, over 160 Saccharomyces sp. strains, mainly isolated from breweries and distilleries, were screened for tolerance to lignocellulosic inhibitors. Three Saccharomyces cerevisiae strains, YB-2625, Y-7567, and Y-1649, were selected for more in depth analysis using varying concentrations of individual inhibitors and acid hydrolyzed corn stover. Performance among the strains and established commercial strains varied depending on the inhibitor present. Growth assays with individual inhibitors demonstrated that detoxification of HMF and furfural impact yeast differently as detoxification of high concentrations of HMF results in a large increase in the production of acetate, combined with a lesser increase in production of glycerol, which is not found in the detoxification of furfural. In fermentations using corn stover hydrosylates, YB-2625 and Y-7567, demonstrated a reduced lag phase and higher growth relative to an established commercial strain and a strain from a previous screen. Genome sequencing of the two strains showed that while both strains have some genes previously associated with inhibitor tolerance, they do not have the full complement of genes, as found in a number of inhibitor-tolerant strains sequenced to date. This suggests that while these genes may aid in increased inhibitor tolerance, additional genes or overall genetic background may also play a role in increased inhibitor tolerance.