of organic synthesis. Species from the following genera are known to synthesize B 12 : Acetobacterium , Aerobacter , Agrobacterium , Alcaligenes , Azotobacter , Bacillus , Clostridium , Corynebacterium , Flavobacterium , Lactobacillus , Micromonospora , Mycobacterium , Nocardia , Propionibacterium , Protaminobacter , Proteus , Pseudomonas , Rhizobium ,