Overexpression of NAD kinase in recombinant Escherichia coli harboring the phbCAB operon improves poly(3-hydroxybutyrate) production.
NAD kinase was overexpressed to enhance the accumulation of poly(3-hydroxybutyrate) (PHB) in recombinant Escherichia coli harboring PHB synthesis pathway via an accelerated supply of NADPH, which is one of the most crucial factors influencing PHB production. A high copy number expression plasmid pE76 led to a stronger NAD kinase activity than that brought about by the low copy number plasmid pELRY. Overexpressing NAD kinase in recombinant E. coli was found not to have a negative effect on cell growth in the absence of PHB synthesis. Shake flask experiments demonstrated that excess NAD kinase in E. coli harboring the PHB synthesis operon could increase the accumulation of PHB to 16-35 wt.% compared with the controls; meanwhile, NADP concentration was enhanced threefold to sixfold. Although the two NAD kinase overexpression recombinants exhibited large disparity on NAD kinase activity, their influence on cell growth and PHB accumulation was not proportional. Under the same growth conditions without process optimization, the NAD kinase-overexpressing recombinant produced 14 g/L PHB compared with 7 g/L produced by the control in a 28-h fermentor study. In addition, substrate to PHB yield Y (PHB/glucose) showed an increase from 0.08 g PHB/g glucose for the control to 0.15 g PHB/g glucose for the NAD kinase-overexpressing strain, a 76% increase for the Y (PHB/glucose). These results clearly showed that the overexpression of NAD kinase could be used to enhance the PHB synthesis.
Li
Zheng-Jun
ZJ
Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing, China.
Cai
Lei
L
Wu
Qiong
Q
Chen
Guo-Qiang
GQ
D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000235:genetics / Q000378:metabolism*; D015870:Gene Expression; D006885:Hydroxybutyrates / Q000378:metabolism*; D009249:NADP / Q000378:metabolism; D009876:Operon; D010770:Phosphotransferases / Q000235:genetics / Q000378:metabolism*; D011091:Polyesters / Q000378:metabolism*; D000094122:Polyhydroxybutyrates
D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D006885:Hydroxybutyrates; D009249:NADP; D010770:Phosphotransferases; D011091:Polyesters; C003182:poly-beta-hydroxybutyrate; D000094122:Polyhydroxybutyrates; C434675:NadK protein, E coli