Accumulation of d-glucose from pentoses by metabolically engineered Escherichia coli.

Escherichia coli that is unable to metabolize D-glucose (with knockouts in ptsG, manZ, and glk) accumulates a small amount of D-glucose (yield of about 0.01 g/g) during growth on the pentoses D-xylose or L-arabinose as a sole carbon source. Additional knockouts in the zwf and pfkA genes, encoding, respectively, D-glucose-6-phosphate 1-dehydrogenase and 6-phosphofructokinase I (E. coli MEC143), increased accumulation to greater than 1 g/liter D-glucose and 100 mg/liter D-mannose from 5 g/liter D-xylose or L-arabinose. Knockouts of other genes associated with interconversions of D-glucose-phosphates demonstrate that D-glucose is formed primarily by the dephosphorylation of D-glucose-6-phosphate. Under controlled batch conditions with 20 g/liter D-xylose, MEC143 generated 4.4 g/liter D-glucose and 0.6 g/liter D-mannose. The results establish a direct link between pentoses and hexoses and provide a novel strategy to increase carbon backbone length from five to six carbons by directing flux through the pentose phosphate pathway.