Engineering stress-tolerant microbes for lower cost production of biofuels and bioproducts

Efficient fermentation processes to produce ethanol from both the hexose and pentose sugars available in low-cost lignocellulosic biomass are sought to support the expansion of the biofuels industry. Furfural and hydroxymethylfurfural (HMF) are key byproducts of the dilute acid pretreatment hydrolysis of lignocellulosic biomass, the most economical method of releasing hemicellulosic sugars for fermentation to ethanol biofuel. A discussion on engineering stress tolerant microbes for lower cost production of biofuels and bioproducts covers gathering fundamental knowledge about the metabolic, physiologic, and genetic mechanisms underlying inhibitor tolerance of ethanologenic yeast strains; natural strains of the yeasts Saccharomyces cerevisiae and Pichia stipitis, which can survive and adapt to the presence of furfural and HMF; exposure to gradually increasing levels of each inhibitor; fermentation analysis of adapted strains; the role of in situ detoxification in inhibitor-tolerant strains; tolerance to furfural and HMF; tolerant strains, with emphasis on heir expression profiles; and process-based strategies to produce a tolerant initial population and then to foster and sustain tolerance during growth and ethanol fermentation. This is an abstract of a paper presented at the AIChE Annual Meeting and Fall Showcase (Cincinnati, OH 10/30/2005-11/4/2005).