Serine affects engulfment during the sporulation process in Clostridium perfringens strain SM101.

Objectives: Although Clostridium perfringens sporulation is a key event in the pathogenesis of food-borne illness, the molecules and underlying mechanisms responsible for regulating sporulation are incompletely understood. The present study sought to identify amino acids that affect sporulation in C. perfringens strain SM101.

Methods: A C. perfringens strain was cultured in the chemically defined medium deficient in an amino acid. The bacterial growth was determined by spectrophotometrically measuring culture turbidity and by calculating colony-forming unit. Morphological characteristics were assessed by phase-contrast microscopy with fluorescent staining and by electron microscopy.

Results: The amino acids Arg, Cys, Gly, His, Ile, Leu, Met, Phe, Thr, Trp, Tyr, and Val were important for sporulation, and furthermore, Ser reduced sporulation. The mechanism underlying Ser-induced prevention of sporulation was assessed morphologically. The numbers of bacterial cells in sporulation stage II were significantly higher in the presence than in the absence of Ser. In the presence of Ser, almost all cells were in stage II-III, characterized by polar septation-early engulfment, and did not proceed to late engulfment.

Conclusions: These results suggest that Ser accelerated the early stage of sporulation of C. perfringens strain SM101, but disturbed the engulfment process, resulting in reduction of sporulation. To the best of our knowledge, this is the first study reporting that an amino acid affects engulfment during the C. perfringens sporulation process.