The group of ZHANG Dawei divided the vitamin B12 biosynthesic pathway into six modules into which they engineered a total of 28 genes from R. capsulatus, Brucella melitensis, Sinorhizobium meliloti 320, ,S. typhimurium, and Rhodopseudomonas palustris. Each module was expressed in E. coli on individual plasmids or incorporated into the E. coli genome. After metabolic engineering to ameliorate cobalt chelation and remove module 4 bottlenecks, as well as optimization of fermentation conditions, vitamin B12 production was increased 250fold to 307 µg per g dry cell.
https://www.nature.com/articles/s41467-018-07412-6
CAS news release, November 26, 2018
CAS Institute of Industrial Biotechnology achieves vitamin-B12 synthesis in E. coli using synthetic biology