EFFECTS OF ANTIBIOTICS ON SYNTHESIS AND PERSISTENCE OF SIGMA-E IN SPORULATING BACILLUS-SUBTILIS

A potential regulatory link between the activation of a sporulation-specific sigma factor (σ(E)) and forespore septum formation was investigated by treating Bacillus subtilis with inhibitors of protein or peptidoglycan synthesis and monitoring the consequences of these treatments on σ(E) activation and septation. Western blot (immunoblot) and electron microscopic analyses revealed that both the formation of σ(E) and septation were inhibited to a similar degree when either rifampin or chloramphenicol was added at different times before the second hour into sporulation but that penicillin preferentially blocked septation. We interpret these results as indicating that the syntheses of the gene products for both septation and σ(E) activation occur at approximately the same time in development but that synthesis of an intact septum is unlikely to be a prerequisite for the formation of σ(E). We observed that penicillin could not only block septation but, depending on the time of its addition, could also inhibit both the activation of σ(E) and the synthesis of its precursor. The basis of this effect is unknown, but it is not due to an overall disruption of protein synthesis. The incorporation of [35S]methionine by the sporulating cultures was unaffected by penicillin treatment. A time course study of the effect of rifampin and chloramphenicol treatments on σ(E) levels revealed that both the synthesis of σ(E) and its disappearance from sporulating cultures is inhibited by these antibiotics. This suggests that ongoing macromolecular synthesis is required for the turnover of σ(E).