A Clostridium perfringens hem gene cluster contains a cysG(B) homologue that is involved in cobalamin biosynthesis

The hem gene cluster, which consists of hemA, cysG(B), hemC, hemD, hemB, an d hemL genes, and encodes enzymes involved in the biosynthetic pathway from glutamyl-tRNA to uroporphyrinogen III, has been identified by the cloning and sequencing of two overlapping DNA fragments from Clostridium perfringen s NCTC8237, The deduced amino acid sequence of the N-terminal region of C. perfringens HemD is homologous to those reported for the C-terminal region of Salmonella typhimurium CysG and Clostridium josui HemD, C, perfringens C ysG(B) is a predicted 220-residue protein which shows homology to the N-ter minal region of S. typhimurium CysG. Disruption of the cysG(B) gene in C. p erfringens strain 13 by homologous recombination reduced cobalamin (vitamin Bit) levels by a factor of 200, When grown in vitamin B-12-deficient mediu m, the mutant strain showed a four-fold increase in its doubling time compa red with that of the wild-type strain, and this effect was counteracted by supplementing the medium with vitamin B-12, These results suggest that C. p erfringens CysG(B) is involved in the chelation of cobalt to precorrin II a s suggested for the CysG(B) domain of S, typhimurium CysG, enabling the syn thesis of cobalamin.