Increased Furfural Tolerance Due to Overexpression of NADH-Dependent Oxidoreductase FucO in Escherichia coli Strains Engineered for the Production of Ethanol and Lactate
ABSTRACTFurfural is an important fermentation inhibitor in hemicellulose sugar syrups derived from woody biomass. The metabolism of furfural by NADPH-dependent oxidoreductases, such as YqhD (lowKmfor NADPH), is proposed to inhibit the growth and fermentation of xylose inEscherichia coliby competing with biosynthesis for NADPH. The discovery that the NADH-dependent propanediol oxidoreductase (FucO) can reduce furfural provided a new approach to improve furfural tolerance. Strains that produced ethanol or lactate efficiently as primary products from xylose were developed. These strains included chromosomal mutations inyqhDexpression that permitted the fermentation of xylose broths containing up to 10 mM furfural. Expression offucOfrom plasmids was shown to increase furfural tolerance by 50% and to permit the fermentation of 15 mM furfural. Product yields with 15 mM furfural were equivalent to those of control strains without added furfural (85% to 90% of the theoretical maximum). These two defined genetic traits can be readily transferred to enteric biocatalysts designed to produce other products. A similar strategy that minimizes the depletion of NADPH pools by native detoxification enzymes may be generally useful for other inhibitory compounds in lignocellulosic sugar streams and with other organisms.