Submitted to: Fermentation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/6/2020
Publication Date: 11/10/2020
Citation: Nichols, N.N., Hector, R.E., Mertens, J.A., Frazer, S.E. 2020. Abatement of inhibitors in recycled process water from biomass fermentations relieves inhibition of a Saccharomyces cerevisiae penthose phosphate pathway mutant. Fermentation. 6(4). Article 107. https://doi.org/10.3390/fermentation6040107.
DOI: https://doi.org/10.3390/fermentation6040107

Interpretive Summary: Agricultural residues and energy crops, which are collectively termed biomass, are important sources of sugars from which fuels and chemicals can be produced. Unfortunately, attempts to convert biomass sugars to such products are often thwarted by chemicals that inhibit the microbes meant to do the conversions. This study probed the nature of that inhibition using yeast strains defective in tolerance to inhibitors, salt, or osmolarity (a measure of dissolved materials). The inhibitor-sensitive yeast was unable to ferment xylose, an important biomass sugar, and its performance was rescued by biological steps to remove inhibitors. The salt-sensitive and osmolarity-sensitive mutants were not affected. Recycling of water in a fermentation process is important to reduce waste and environmental footprint. Fermentation of the recycled process water could also be rescued by biological inhibitor removal, allowing successful fermentation with reused process water. This research will be useful for fuel and chemical producers that are interested in managing their water footprint, to inform recycle of cellulosic fermentation related process water.

Technical Abstract: Pretreatment of lignocellulosic biomass to unlock sugars for bioconversion leads to formation of chemicals that are inhibitory to enzymes and fermenting microbes. Understanding the nature of fermentation inhibition in biomass hydrolysates and recycled fermentation process water is important for conversion of biomass to fuels and chemicals. This study used three mutants disrupted in genes important for either tolerance to oxidative stress, salinity, or osmolarity to ferment biomass hydrolysates in a xylose-fermenting Saccharomyces cerevisiae strain. The S. cerevisiae ZWF1 mutant with heightened sensitivity to fermentation inhibitors was unable to ferment corn stover dilute-acid hydrolysate, but conditioning of hydrolysate using a fungal strain, Coniochaeta ligniaria, to consume inhibitors yielded successful fermentation of the hydrolysate. Growth of two other strains, a salt-sensitive HAL4 mutant and a GPD1 mutant sensitive to osmotic stress, was not negatively affected in hydrolysate compared to the parent xylose-metabolizing strain. In recycled fermentation process water, inhibition of the ZWF1 mutant could again be remediated by biological abatement, and no effect on growth was observed for any of the mutants compared to the parent strain.