• The Aerobic Pathway is exploited by organisms like Pseudomonas denitrificans and Bacillus megaterium. The biosynthesis of B₁₂ by this mechanism is thought to require molecular oxygen. Notably, the central cobalt atom is inserted very late in the reaction sequence.
  
• The Anaerobic Pathway is exploited by organisms Propionibacterium sherminni (now Pr. freudenreichii) and Salmonella typhimurium. The biosynthesis of B₁₂ by this mechanism is thought to be toxified by molecular oxygen. Notably, the central cobalt atom is inserted very early in the reaction sequence.
• As noted in the Aerogenes Zone, Klebsiella aerogenes and other enteric bacteria appear to make B₁₂ under both aerobic and anaerobic conditions. This laboratory is analyzing K. aerogenes using genetic and molecular approaches to determine how this is done.

Consult these separate pathways for the biosynthesis of Amino-propanol and Dimethylbenzumidazole (DMB), essential components of coenzyme B₁₂.