A paracrystalline inclusion formed during sporulation of enterotoxin-producing strains of Clostridium perfringens type A.

A large paracrystalline inclusion is formed by certain strains of Clostridium perfringens type A during spore morphogenesis. In most cell thin sections, the inclusion appeared rod-shaped when sectioned at an angle perpendicular to its longer axis, and circular or oval-shaped when sectioned at an angle parallel to its longer axis. Measurements performed on electron micrographs of inclusions sectioned to reveal the rod shape indicated a fairly consistent thickness (width) of 192 +/- 23 nm. The length of the inclusions varied considerably with a maximum of approximately 2,120 nm being observed. Ultrastructurally, the inclusion was composed of closely packed, periodically spaced, parallel layers. Usually a single inclusion was randomly located in the cytoplasm of the cell. Two inclusions per cell were rarely observed. The inclusion was formed only by ent(+) strains of C. perfringens. Mutants of the ent(+) strain NCTC 8798 that were altered in their sporulating and enterotoxin-producing capacities and revertants of these mutants were tested for inclusion formation. The results indicate that, as with the ent(+) trait, a direct relationship exists between inclusion formation and spore formation. The synthesis of enterotoxin, formation of a morphologically distinct inclusion, and the initial deposition of discontinuous coat fragments around the forespore appear to be events closely related in time during spore morphogenesis.