Effect of NADH kinase on poly-3-hydroxybutyrate production by recombinant Escherichia coli.

The cofactor NADPH participates in a variety of anabolic reactions and its availability is considered to play a critical role in biotransformation processes. NADH kinase (Pos5) from Saccharomyces cerevisiae catalyzes the phosphorylation of NADH to generate NADPH. To investigate the effect of NADH kinase on poly-3-hydroxybutyrate (PHB) production, pos5 was co-expressed with PHB synthetic operon phbCAB in Escherichia coli. The recombinant strain carrying pos5 and phbCAB co-expression plasmid reached 5.96 g/L cell dry weight with 64.1% PHB accumulation in 72 h shake flask cultivation, while the control strain without pos5 yielded 3.93 g/L cell dry weight with 58.5% PHB content. PHB production titer was enhanced from 2.30 g/L to 3.82 g/L. Intracellular cofactor concentration analysis revealed that the ratio of NADP/NAD in pos5 overexpression strain was two times more compared with that of the control without pos5. The results showed that NADH kinase could be employed as an effective metabolic manipulation target to improve PHB synthesis.