Fig. 1
From: Microbial production of vitamin B12: a review and future perspectives
Biosynthetic pathways of tetrapyrrole compounds. ALA is synthesized by either the C4 or the C5 pathway. Adenosylcobalamin is synthesized via the de novo or via salvage pathways. The enzymes shown in the adenosylcobalamin biosynthetic pathway originate from P. denitrificans or S. typhimurium, which either use the aerobic pathway or the anaerobic pathway, respectively