METABOLIC ENGINEERING OF BACTERIA FOR ETHANOL-PRODUCTION

Technologies are available which will allow the conversion of lignocel lulose into fuel ethanol using genetically engineered bacteria. Assemb ling these into a cost-effective process remains a challenge. Our work has focused primarily an the genetic engineering of enteric bacteria using a portable ethanol production pathway. Genes encoding Zymomonas mobilis pyruvate decarboxylase and alcohol dehydrogenase have been int egrated into the chromosome of Escherichia coli B to produce strain KO 11 for the Fermentation of hemicellulose-derived syrups. This organism can efficiently ferment ail hexose and pentose sugars present in the polymers of hemicellulose. Klebsiella oxytoca M5A1 has been geneticall y engineered in a similar manner to produce strain P2 for ethanol prod uction from cellulose. This organism has the native ability to ferment cellobiose and cellotriose, eliminating the need for one class of cel lulase enzymes. The optimal pH for cellulose fermentation with this or ganism (pH 5.0-5.5) is near that of fungal cellulases. The general app roach for the genetic engineering of new biocatalysts has been most su ccessful with enteric bacteria thus far. However, this approach may al so prove useful with Gram-positive bacteria which have other important traits for lignocellulose conversion. Many opportunities remain for f urther improvements in the biomass to ethanol processes, These include the development of enzyme-based systems which eliminate the need for dilute acid hydrolysis or other pretreatments, improvements in existin g pretreatments for enzymatic hydrolysis, process improvements to incr ease the effective use of cellulase and hemicellulase enzymes, improve ments in rates of ethanol production, decreased nutrient costs, increa ses in ethanol concentrations achieved in biomass beers, increased res istance of the biocatalysts to lignocellulosic-derived toxins, etc. To be useful, each of these improvements must result in a decrease in th e cost for ethanol production. (C) 1998 John Wiley & Sons, Inc.