Vitamin B12 is commercially produced using:
Vitamin B12, cobalamin, featuring corrin ring coordinating cobalt ion, requires approximately thirty enzymatic steps making chemical synthesis with 60 steps economically unviable, so industrial production entirely depends on microbial fermentation. Propionibacterium freudenreichii and Propionibacterium shermanii, propionic acid bacteria used in Swiss cheese ripening, synthesize active cobalamin via anaerobic pathway where cobalt inserted early into precorrin-2 by CbiK chelatase, distinct from aerobic Pseudomonas denitrificans pathway inserting cobalt late. Gene clusters cob and cbi encode meth
Ref: Martens et al. Applied Microbiology Biotechnology 2002 Vitamin B12 fermentation; Lehninger Ch B-vitamin biosynthesis pathways.