Enhanced production of poly-3-hydroxybutyrate by recombinant Escherichia coli containing NAD kinase and phbCAB operon

With the help of Tn5 transposon technique, gene yfjB encoding NAD kinase in Escherichia coli ( E . coli ) was inserted into chromosome of recombinant E . coli polyhydroxybutyrate (PHB) containing PHB synthesis operon integrated in the host genome. After successful transposition of an extra yfjB gene copy into genome, the selected recombinant named E . coli PHBTY4 showed stronger NAD kinase activity than that of E . coli PHB. Shake flask studies suggested that both cell dry weight and PHB accumulation were significantly increased in E . coli PHBTY4 compared with that of the control. E . coli PHBTY4 produced approximately 23 g/L PHB compared with its control which synthesized only 10 g/L PHB when grown under the same conditions in a 6 L fermentor after 32 h of cultivation. In addition, E . coli PHBTY4 maintained high genetic stability during the cultivation processes. These results revealed a practical method to construct genetically stable strains harboring extra NAD kinase gene to enhance NADP(H)-dependent bio-reactions.