Development of auxotrophic selection system for improved coenzyme B12 production

Abstract

Coenzyme B12 is an important cofactor involved in various metabolism and widely used in food, additives, and pharmaceuticals. Demand for coenzyme B12 steadily grows, but its chemical synthesis is highly complicated because of its complex structure. Microbial production of coenzyme B12 has recently attracted attention as an alternative. Especially using well-characterized microorganisms such as Escherichia coli as a host could be an efficient strategy for further engineering. In this study, we designed a novel strategy to improve the production of coenzyme B12 in previously engineered coenzyme B12 producing E. coli. First, the synthetic coenzyme B12 auxotrophic system was developed by using coenzyme B12–dependent methionine synthases with deletion of coenzyme B12-independent methionine synthase in E. coli. The synthetic auxotroph system showed coenzyme B12-dependent auxotrophic growth. Then it was applied to coenzyme B12 producing strain, resulting in improvement of the specific production of coenzyme B12 by modulating plasmid copy numbers. Although the auxotroph system has severely reduced cell biomass due to insufficient methionine synthesis, additional engineering of the auxotroph system by the varied expression level of metH could significantly improve cell biomass and coenzyme B12 production. Consequently, we demonstrated that our novel strategy can be effectively used to improve coenzyme B12 production, and it could be further applied to other coenzyme B12 producing strains.