Induction of antibiotic production by protease in Bacillus brevis (ATCC 8185)

Bacillus brevis (ATCC 8185) produces an antibiotic peptide, linear gramicidin, in the early stationary growth phase. Since we observed that preculture in milk medium is essential for production of the antibiotic in broth medium, we studied the role of the preculture in the antibiotic production. We found that addition of the supernatant of the precultured milk medium was sufficient to induce gramicidin production in broth medium. Fresh milk medium had no effect. The effector substance in the overnight cultured milk medium was labile at both acidic and alkaline pH and was destroyed by heat. We also found that addition of a protease (for example, bovine pancreas chymotrypsin or Streptomyces griseus protease) instead of the supernatant could induce the gramicidin production. Addition of Mn2+ was not required for the protease-induced production of gramicidin. It is known that B. brevis cells secrete protease into milk medium. But neither use of the protease-pretreated broth medium nor addition of casamino acids to broth medium induced gramicidin production. These results suggest that B. brevis cells secrete a factor for linear gramicidin production, that the inducing factor is protease and that the target of the protease is a substance(s) produced by the bacteria.