Accumulation of D-Glucose from pentoses by Escherichia coli

Escherichia coli unable to metabolize D-glucose (knockouts in ptsG, manZ, 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 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/L D-glucose and about 100 mg/L D-mannose from 5 g/L 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-6P.  Under controlled batch conditions with 20 g/L D-xylose, MEC143 generated 4.4 g/L D-glucose and 0.6 g/L 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.

 Key words:     L-arabinose; D-glucose-6-phosphate 1-dehydrogenase; pentose phosphate pathway; 6-phosphofructokinase I; glucose-6P isomerase; D-xylose