Multilevel metabolic engineering for enhanced synthesis of S-adenosylmethionine by Bacillus amyloliquefaciens.

Objectives: To enhance the de novo synthesis of SAM, the effects of several key genes on SAM synthesis were examined based on modular strategy, and the key genes were manipulated to obtain an engineered strain with high SAM production.

Results: In Bacillus amyloliquefaciens HSAM6, the deletion of argG gene to block aspartic acid branching degradation increased SAM titer to 254.78 ± 15.91 mg/L, up 18% from HSAM6. Subsequently, deleting the moaA gene to boost the supply of 5-methyltetrahydrofolate led to the stunted growth and the plummeting yield of SAM. Further improvement of strain growth by overexpression of the citA gene, while SAM synthesis was not significantly enhanced. Finally, the maximum SAM titer (452.89 ± 13.42 mg/L) was obtained by overexpression SAM2 gene using the multicopy plasmid.

Conclusions: The deletion of argG gene and the overexpression of SAM2 gene significantly improved SAM synthesis in B. amyloliquefaciens.