Tyrocidine is a cyclic decapeptide antibiotic which is produced and secreted by stationary-phase cells of the sporeforming bacterium Bacillus brevis. We identified the promoter for the B. brevis structural gene (tycA) for tyrocidine synthetase I, the enzyme catalyzing the first step in tyrocidine biosynthesis, and studied its regulation in cells of B. brevis and Bacillus subtilis. Transcription from the tycA promoter was induced at the end of the exponential phase of the growth cycle in B. brevis cells growing in sporulation medium. To study the regulation of tycA in B. subtilis, we constructed a derivative of the B. subtilis bacteriophage SPβ containing a transcriptional fusion of the tycA promoter to the lacZ gene of Escherichia coli and introduced the tycA-lacZ operon fusion by means of specialized transduction into sporulation mutants known to be blocked in sporulation-associated antibiotic production. Our principal finding was that tycA-directed lacZ expression was impaired in the stage-0 mutants with mutations spo0A, spo0B, and spo0E but not in spo0C, spo0F, spo0H, or spo+ bacteria. The dependence on the spo0A gene product could be entirely bypassed by an abrB suppressor mutation, which caused tycA-lacZ to be transcribed constitutively at all stages of growth. A simple model is proposed for the mechanism of tycA induction based on the Spo0A-dependent inactivation of AbrB protein, which is proposed to be a negative regulator of tycA transcription.
ASJC Scopus subject areas
- Molecular Biology