Metabolic Engineering of Corynebacterium glutamicum for the Production of L-Ornithine

Abstract

L-ornithine is a non-essential amino acid for various industrial applications in food industry. In this study, Corynebacterium glutamicum ATCC 13032 was metabolically engineered for the production of L-ornithine. First, the proB and argF genes were deleted to block the competitive branch pathway and to block the conversion of L-ornithine to citrulline, respectively. In addition, the argR gene encoding the regulatory repressor of the L-arginine operon was also deleted. The resulting strain produced 230 mg/L of L-ornithine from glucose in flask culture. This base strain was further engineered by the plasmid-based overexpression of the argCJBD genes from C. glutamicum ATCC 21831, which resulted in the production of 7.19 g/L of L-ornithine. To enrich the NADPH pool, the carbon flux was redirected towards the pentose phosphate pathway by changing the start codons of the pgi and zwf genes and replacing the native promoter of the tkt operon with the strong sod promoter. Fed-batch cultivation of this final strain YW06 (pSY223) allowed production of 51.5 g/L of L-ornithine in 40 h with the overall productivity of 1.29 g/L/h. The results obtained in this study demonstrate the possibility of efficiently producing L-ornithine by metabolically engineered C. glutamicum.