Four new genes, and the enzymes that they encode, are disclosed, which are present in Propionibacterium freudenreichii, and which are involved in at least five steps in the biosynthetic pathway of vitamin B.sub.12. The four enzymes are: A: cobyrinic acid a, c-diamide synthase; B: a bifunctional enzyme, which is a cobinamide kinase and a cobinamide phosphate guanyl transferase; C: a cobalamin 5-phosphate synthase; and D: an adenosyl transferase. Genes encoding the four enzymes can be placed in Propionibacteria shuttle vectors and used to transform Propionibacteria hosts, in order to improve the production of vitamin B.sub.12 or a precursor thereof on an industrial scale during fermentation.