Stress biology of yeasts: The breeding of bioethanol-producing yeast by detoxification of glycolaldehyde, a novel fermentation inhibitor

Abstract

The inhibitory effect of lignocellulose hydrolysates poses a significant technological barrier to the industrialization of second-generation bioethanol production. Even though approximately 60 inhibitory compounds have been reported to be present in lignocellulose hydrolysates, we discovered glycolaldehyde as a novel fermentation inhibitor and established a key role for the toxic compound in second-generation bioethanol production. Glycolaldehyde is primarily generated from retro-aldol condensation of monomeric sugars liberated during the lignocellulosic biomass pretreatment process. It substantially inhibits yeast growth and ethanol fermentation at a very low concentration. Moreover, glycolaldehyde is a stronger growth inhibitor than other reported major fermentation inhibitors such as 5-hydroxymethyl furfural (5-HMF) and furfural. Through comprehensive genomic analysis and in-depth analysis of fermentation metabolic consequences in response to redox cofactor perturbation with glycolaldehyde, we discovered the toxic mechanisms and pathways necessary to ultimately engineer a glycolaldehyde-tolerant yeast strain. This chapter provides novel knowledge on glycolaldehyde toxicity and molecular mechanisms for in situ biological detoxification of glycolaldehyde to improve the bioethanol fermentation of Saccharomyces cerevisiae.