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, and 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 perfringens 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 CysG(β) is a predicted 220-residue protein which shows homology to the N- terminal region of S. typhimurium CysG. Disruption of the cysG(β) gene in C. perfringens strain 13 by homologous recombination reduced cobalamin (vitamin B₁₂ levels by a factor of 200. When grown in vitamin B₁₂-deficient medium, the mutant strain showed a four-fold increase in its doubling time compared with that of the wild-type strain, and this effect was counteracted by supplementing the medium with vitamin B₁₂. These results suggest that C. perfringens CysG(β) is involved in the chelation of cobalt to precorrin II as suggested for the CysG(β) domain of S. typhimurium CysG, enabling the synthesis of cobalamin.