COBALAMIN (VITAMIN-B-12) BIOSYNTHESIS - IDENTIFICATION AND CHARACTERIZATION OF A BACILLUS-MEGATERIUM COBI OPERON

A 16 kb DNA fragment has been isolated from a Bacillus megaterium geno mic library and fully sequenced. The fragment contains 15 open reading frames, 14 of which are thought to constitute a B. megaterium cobalam in biosynthetic (cob) operon. Within the operon, II genes display simi larity to previously identified Salmonella typhimurium cobalamin biosy nthetic genes (cbiH(60), -J, -C, -D, -ET, -L, -F, -G, -A, cysG(A) and btuR), whereas three do not (cbiW, -X and -Y). The genes of the B. meg aterium cob operon were compared with the cobalamin biosynthetic genes of Pseudomonas denitrificans, Methanacoccus jannaschii and Synechocys tis sp. Taking into account the presence of cbiD and cbiG, the absence of a cobF, cobG and cobN, -S and -T, it was concluded that B. megater ium, M. jannaschii and Synechocystis sp., like S. typhimurium, synthes ize cobalamin by an anaerobic pathway, in which cobalt is added at an early stage and molecular oxygen is not required.