Protaminobacter , Proteus , Pseudomonas , Rhizobium , Salmonella , Serratia , Streptomyces , Streptococcus and Xanthomonas . Industrial production of B 12 is through fermentation of selected microorganisms. [ 36 ] Streptomyces griseus , a bacterium once thought to be a yeast, was the commercial source of vitamin B 12