Identification and characterization of a putative endolysin encoded by episomal phage phiSM101 of Clostridium perfringens.

Clostridium perfringens produces potent toxins and histolytic enzymes, causing various diseases including life-threatening fulminant diseases in humans and other animals. Aiming at utilizing a phage endolysin as a therapeutic alternative to antibiotics, we surveyed the genome and bacteriophage sequences of C. perfringens. A phiSM101 muramidase gene (psm) revealed by this study can be assumed to encode an N-acetylmuramidase, since the N-terminal catalytic domain deduced from the gene shows high homology of those of N-acetylmuramidases. The psm gene is characteristic in that it is present in phiSM101, an episomal phage of enterotoxigenic C. perfringens type A strain, SM101, and also in that homologous genes are present in the genomes of all five C. perfringens toxin types. The psm gene was cloned and expressed in Escherichia coli as a protein histidine-tagged at the N-terminus (Psm-his). Psm-his was purified to homogeneity by nickel-charged immobilized metal affinity chromatography and anion-exchange chromatography. The purified enzyme lysed cells of all C. perfringens toxin types but not other clostridial species tested, as was shown by a turbidity reduction assay. These results indicate the Psm-his is useful as a cell-wall lytic enzyme and also suggest that it is potentially useful for biocontrol of this organism.