PsrfA: a ComA-dependent promoter of Bacillus subtilisFigure 1: The regulatory system for competence development in Bacillus subtilis. The development of genetic competence is stimulated by quorum sensing due to the secretion of the ComX pheromone and its accumulation in the surrounding medium. (Modified from: Jung et al.)
Usage and Biology
This promoter is controlled by the well-studied regulatory system for competence development in Bacillus subtilis (Figure 1).
B. subtilis constantly secretes the ComX pheromone (BBa_K2273000), a 9- to 10-amino acid oligopeptide, as a signalling molecule (a). By rising cell-density, the ComX-concentration in the surrounding medium increases until it reaches a threshold and activates ComP, a membrane-spanning protein kinase (b). This mechanism is called quorum sensing.
The kinase reacts to the accumulation of ComX by phosphorylating the response regulator ComA (c) which then works as a transcription factor by binding to several promoters and enhancing their activity (d).
The most important promoter regulated by ComA and involved in competence development is the promoter of the srfA operon (PsrfA). This operon contains not only genes for the production of the antibiotic surfactin (e) but also for ComS (f), another small peptide that prevents the degradation of the autoregulated transcription factor ComK (g). Since the promoter is not only dependent on quorum sensing but also on nutritional conditions, we evaluated the influence of different media (Figure 2). We tested full medium (LB) as well as minimal media (MNGE, MCSE).
Figure 2: Growth (A) and promoter activity of PsrfA (B) in different media. Wild type (WT, pink) and comX-knockout strains (ΔcomX, dark blue) contain a PsrfAluxABCDE fusion.
