Enhanced production of ε-caprolactone by overexpression of NADPH-regenerating glucose 6-phosphate dehydrogenase in recombinant Escherichia coli harboring cyclohexanone monooxygenase gene

Whole-cell conversion of cyclohexanone to ε-caprolactone was attempted by recombinant Escherichia coli BL21(DE3) expressing cyclohexanone monooxygenase (CHMO) of Acinetobacter calcoaceticus NCIMB 9871. High concentrations of cyclohexanone and ε-caprolactone reduced CHMO-mediated bioconversion of cyclohexanone to ε-caprolactone in the resting recombinant E. coli cells. Metabolically active cells were employed by adopting a fed-batch culture to improve the production of ε-caprolactone from cyclohexanone. A glucose-limited fed-batch Baeyer-Villiger oxidation where a cyclohexanone level was maintained less than 6 g/l resulted in a maximum ε-caprolactone concentration of 11.0 g/l. The maximum ε-caprolactone concentration was improved further to 15.3 g/l by coexpression of glucose-6-phosphate dehydrogenase, an NADPH-generating enzyme encoded by the zwf gene which corresponded to a 39% enhancement in ε-caprolactone concentration compared with the control experiment performed under the same conditions.