Development of a fermentation strategy to enhance the catalytic efficiency of recombinant Escherichia coli for l-2-aminobutyric acid production

Microbial fermentation for enzyme production and then whole-cell catalysis for l-2-aminobutyric acid (l-ABA) production have huge potential for industrial application, but the catalytic capacities of cells are directly related to the fermentation process. Using a 50 L fermenter, the effects of initial glycerol concentration in the medium and rotating speed on cell catalytic capacity were investigated. Fermentation cells showed the best catalytic activity when the initial glycerol concentration was 12 g/L and the rotating speed was 250 rpm. Furthermore, we studied the difference between glycerol and glycerol mixtures as fed-batch media in pH-stat fed-batch fermentation. Results showed that glycerol had better catalytic activity than the glycerol mixture, and the effect of fed-batch fermentation was better than batch fermentation. Meanwhile, the enzyme activities of leucine dehydrogenase and formate dehydrogenase reached 129.87 U/g DCW and 437.02 U/g DCW, respectively, and the intracellular NAD(H) concentration reached 14.94 μmol/g DCW. Using the optimized fermentation parameters, amplified fermentation was then carried out in a 5000 L fermenter to demonstrate the industrial production of l-ABA by Escherichia coli BL21.