Introduction of the exogenous NADH coenzyme regeneration system and its influence on intracellular metabolic flux of Paenibacillus polymyxa

The NAD+-dependent formate dehydrogenase (FDH) gene from Candida boidinii was introduced into Paenibacillus polymyxa ZJ-9. The effects of this exogenous gene on the growth of the recombinant strain P. polymyxa XG-1, FDH activity, intracellular NADH and NAD+ level and the synthesis of R,R-2,3-butanediol (R,R-2,3-BD) were determined. Results from the fermentation in the 7.5 L bioreactor showed that the exogenous FDH was highly expressed in the recombinant strain. The titers of NADH, lactic acid, ethanol, NADH/NAD+, and CO2 excretion rate (CER) of the recombinant strain increased considerably, while acetoin and formic acid decreased significantly. The highest titers of R,R-2,3-BD by the recombinant strain in batch and fed-batch fermentation were 36.8 g/L and 51.3 g/L, increased 10.2% and 8.0% compared with the parent strain, respectively. This study confirmed that coenzyme regeneration system can manipulate substance metabolism in bacteria, and is an efficient way for promoting the synthesis of NADH-dependent products.