Bioethanol fermentation by recombinant E. coli FBR5 and its robust mutant FBHW using hot-water wood extract hydrolyzate as substrate

Hemicellulose is a potential by-product currently under-utilized in the papermaking industry. It is a hetero-carbohydrate polymer. For hardwood hemicelluloses, D-xylose is the major component upon depolymerization. At SUNY-ESF, wood extracts were obtained by extracting sugar maple wood chips with hot water at an elevated temperature. The wood extracts were then concentrated and acid hydrolyzed. Ethanologenic bacteria, E. coli FBR5, had a good performance in pure xylose medium for ethanol production. However, FBR5 was strongly inhibited in dilute sulfuric acid hydrolyzate of hot-water wood extract. FBR5 was challenged by hot-water wood extract hydrolyzate in this study. After repeated strain adaptation, an improved strain: E. coli FBHW was obtained. Fermentation experiments indicated that FBHW was resistant to the toxicity of hydrolyzate in the fermentation media of concentrated hydrolyzate, and xylose was completely utilized by the strain to produce ethanol. FBHW was grown in the concentrated hydrolyzate without any detoxification treatment and has yielded 36.8 g/L ethanol.