A Clostridium perfringens hem Gene Cluster Contains a cysG^B Homologue That Is Involved in Cobalamin Biosynthesis

Abstract

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^B is a predicted 220-residue protein which shows homology to the N-terminal region of S. typhimurium CysG. Disruption of the cysG^B 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^B is involved in the chelation of cobalt to precorrin II as suggested for the CysG^B domain of S. typhimurium CysG, enabling the synthesis of cobalamin.