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D-Ribose is a five-carbon sugar used for the commercial production of riboflavin. Kinetic mechanisms of D-ribose biosynthesis from xylose were investigated in the genetically engineered Bacillus subtilis JY200 deficient in transketolase. A transketolase gene (tkt) disruption cassette in plasmid pUNKC was integrated into the chromosomal tkt gene in the wild type B.
subtilis 168. Analysis of culture broth by thin layer chromatography showed that the disruption of tkt allowed B. subtilis JY200 to produce D-ribose. In a batch culture of B. subtilis JY200, a loss of cell viability was observed after glucose depletion. Fed-batch cultivation by feeding a glucose solution as a co-substrate was performed to supply energy to xylose metabolism and to maintain cell viability throughout cultivation. Fed-batch cultivation of B. subtilis JY200 in a complex medium containing 11 g/L xylose and 5 g/L glucose gave the best result of 10.1 g/L D-ribose concentration, 0.24 g/g D-ribose yield and 0.29 g/L-hr productivity, corresponding to 40-, 5- and 12-fold increases compared with those in the batch culture. A kinetic study of D-ribose production in fed-batch cultivations of B. subtilis JY200 suggested that xylose uptake might be
critical to maximize D-ribose biosynthesis from xylose.