Induction of sporulation in Bacillus brevis by peptide antibiotics

Abstract

THE regulatory mechanisms of the process of bacterial sporulation are unknown, although some authors have speculated that sporulation and the synthesis of peptide antibiotics are somehow connected^1–4. Paulus and coworkers proposed that tyrocidine and gramicidin D, both synthesised by Bacillus brevis, may interact with the transcriptional process during sporogenesis⁵. They have isolated a mutant of B. brevis which is unable to synthesise gramicidin D and which produces defective spores. The defects could be cured by exogenous gramicidin D, suggesting that this peptide is involved in sporogenesis⁶. In this report we demonstrate that sporulation of early vegetative growing B. brevis cells can be induced by exogenous tyrothricin, a mixture of tyrocidine and gramicidin D, provided that the cells are exposed to a culture medium lacking the nitrogen source. The induction of sporulation occurs concomitantly with a significant increase in RNA synthesis. The results suggest that sporulation and the action of these two peptides are causally connected. Both peptides may play a positive regulatory role in cell differentiation.