Integration and expression of the Escherichia coli xylose isomerase gene in Schizosaccharomyces pombe

The xyclose isomerase gene in Escherichia coli was cloned complementarily into a Leu2-negative Schizosaccharomyces pombe mutant (ATCC 38399). The subsequent integration of the plasmid into the chromosomal DNA of the host yeast was verified by using the dot blot and southern blot techniques. The expressed xylose isomerase showed activity on a nondenaturing polyacrylamide gel. The expression of xylose isomerase gene was influenced by the concentration of nutrients in the fermentation broth. The yeast possessed a xylose isomerase activity of 20 nmol/min/mg by growing in an enriched medium containing yeast extract-malt extract-peptone (YMP) and d-xylose. The conversion of d-xylose to d-xylulose catalyzed by xylose isomerase in the transformed yeast cells makes it possible to ferment d-xylose with ethanol as a major product. When the fermentation broth contained YMP and 5% (w/v)d-xylose, the maximal ethanol yield and productivity reached 0.42 g/g and 0.19 g/l/h, respectively.