Enhanced cobalamin biosynthesis in Ensifer adhaerens by regulation of key genes with gradient promoters

Cobalamin is an essential human vitamin widely used in the pharmaceutical, food, and feed additive industries and currently produced by bacteria or archaea. Ensifer adhaerens HY-1 is an industrial strain that also produces cobalamin. However production outputs are poor and the specific synthesis pathways require characterization. In this study, the whole genome sequence of E. adhaerens HY-1 was generated and annotated, and genes associated with cobalamin biosynthesis were identified. Then, three genes, CobSV, CobQ, and CobW were identified as the most efficient ones for enhancing cobalamin synthesis. By transcriptome sequencing of E. adhaerens HY-1 cells at different growth stages, 65 endogenous promoters with different gradient strengths were identified. After combined expression of different strength promoters and key genes, a high cobalamin-producing recombinant strain, ‘hmm’ (genotype: PmetH-CobSV-PibpA-CobQ-Pmdh-CobW), was generated. Cobalamin production was 143.8 mg/L in shaking flasks, which was 41.0% higher than the original strain. Cobalamin production was further enhanced to 171.2 mg/L using fed-batch fermentation. Importantly, our data and novel approach provide important references for the analysis of cobalamin synthesis and other metabolites in complex metabolic pathways.