Expression of Synechocystis sp. PCC6803 cyanophycin synthetase in Lactococcus lactis nisin-controlled gene expression system (NICE) and cyanophycin production

Cyanophycin is a natural source of polypetide consisting of aspartic acid as a backbone and arginine as its side chain. After the removal of arginine, the remaining poly-aspartate can be served in numerous industrial and biomedical applications. The synthesis of cyanophycin is catalyzed by cyanophycin synthetase. In this study, we used lactic acid bacteria to produce cyanophycin by nisin-controlled gene expression system (NICE). The cyanophycin synthetase gene cphA of Synechocystis sp. strain PCC6803 was cloned to the vector pNZ8149 followed by transformation into Lactococcus lactis subsp. cremoris NZ3900. The effects of nisin concentrations and the amounts of supplemented aspartic acid and arginine were examined for the production of cyanophycin. Alterations of the terminus of cphA gene were also conducted in an attempt to increase the yield of cyanophycin. An optimal cyanophycin production was noted under a culture condition of log phase induced at 250 ng/mL nisin in M17L medium supplemented with 20 mM arginine and 10 mM aspartic acid. An insertion of glycine residue at the C terminus of cyanophycin synthetase resulted in a yield of 20% of dry cell weight, a 10-fold increase when compared with the wild type. The results showed that recombinant lactic acid bacteria, a GRAS system, could provide an alternative approach of producing cyanophycin suitable for agricultural and biomedical applications.