Metabolic Engineering of Corynebacterium Glutamicum for Cysteine Fermentation

Cysteine is one of the sulfur-containing amino acids and has been utilized for production of pharmaceuticals and cosmetics. Cysteine is mainly produced by extracting from hairs, but awareness to consider the influence of the production process to the safety and environment has been increasing. Therefore, it has been expected that the methods to produce cysteine should be changed to fermentation by microorganisms. We have performed metabolic engineering studies on cysteine fermentation by Corynebacterium glutamicum, which has been utilized for fermentative production of amino acids such as glutamic acid and lysine.

In cysteine biosynthesis pathways, serine O-acetyltransferase (SAT) coded by cysE gene is subjected to feedback inhibition by cysteine. For creating cysteine-producing C. glutamicum strain, we introduced the mutant cysE gene encoding feedback-resistant SAT and the constructed recombinant strain could indeed produce cysteine. Moreover, in order to increase the productivity of cysteine by C. glutamicum, the metabolic engineering strategies were derived by in silico metabolic simulation using a genome-scale metabolic model of C. glutamicum (Shinfuku et al. 2009 Microb. Cell Fact. 8:43). Simulation results suggest that the increase in the metabolic fluxes of the pentose phosphate pathway for enhancement of NADPH supply to sulfate reduction reactions and the increase in acetyl-CoA supply for SAT reaction would be effective to enhance cysteine production by C. glutamicum. In addition, we have examined the effects of overexpression of the genes encoding the possible cysteine exporters on cysteine production by C. glutamicum.

This work is financially supported by the Ministry of Agriculture, Forestry and Fisheries, Japan.