Use of catabolite repression mutants for fermentation of sugar mixtures toethanol

Use of agricultural biomass, other than cornstarch, to produce fuel ethanol requires a microorganism that can ferment the mixture of sugars derived fr om hemicellulose. Escherichia coli metabolizes a wide range of substrates a nd has been engineered to produce ethanol in high yield from sugar mixtures . E. coli metabolizes glucose in preference to other sugars and, as a resul t, utilization of the pentoses in hemicellulose-derived sugar mixtures is d elayed and may be incomplete. Residual sugar lowers the ethanol yield and i s problematic for downstream processing of fermentation products. Therefore , a catabolite repression mutant that simultaneously utilizes glucose and p entoses would be useful for fermentation of complex substrate mixtures. We constructed ethanologenic E. coli strains with a glucose phosphotransferase (ptsG) mutation and used the mutants to ferment glucose, arabinose, and xy lose, singly and in mixtures, to ethanol. Yields were 87-94% of theoretical for both the wild type and mutants, but the mutants had an altered pattern of mixed sugar utilization. Phosphotransferase mutants metabolized the pen toses simultaneously with glucose, rather than sequentially. Based upon fer mentations of sugar mixtures, a catabolite-repression mutant of ethanologen ic E. coli is expected to provide more efficient fermentation of hemicellul ose hydrolysates by allowing direct utilization of pentoses.