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.