Part:BBa_K2273003

ComX pheromone for competence development in Bacillus subtilis

Usage and Biology

Figure 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.)

The development of genetic competence in Bacillus subtilis is stimulated by quorum sensing (Figure 1). B. subtilis constantly secretes the ComX pheromone, 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). 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). (Hamoen et al.)
The most important promoter regulated by ComA and involved in competence development is the promoter of the srfA operon (P_srfA, BBa_K2273000). 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). ComK activates expression of more than 100 genes, including comG, that is part of the transformation machinery (h) (Comella et al.,Susanna et al.). Consequently, B. subtilis can take up DNA from the environment either as direct nutrient source or incorporate the DNA via homologues recombination into its own genome.

We evaluated the influence of an overproduction of the ComX pheromone on the promoters that are listed below.

PsrfA	BBa_K2273000
PrapA	BBa_K2273001
PrapF	BBa_K2273002

Especially for P_srfA we could show ComX-dependence. By using an inducible copy of comX we could compensate comX-deficiency as well (Figure 2).

Figure 2: Growth (A) and promoter activity of various promoters (B) in dependence of xylose-induced ComX-production. Wild type (WT, pink and light blue) and comX-knockout strains (ΔcomX, black and dark blue) contain a promoter-luxABCDE fusion as well as an inducible copy of comX. After 1 hour of incubation (dashed line) the cultures were induced with 1% xylose (light blue and black) or with distilled water (dH2O, pink and dark blue).

The part was created and used by TU_Dresden 2017. All assays have been conducted with B. subtilis W168 carrying the promoter fused to the comX upstream a xylose-inducible promoter (P_xylA). Sequence and Features BBa_K2273003 SequenceAndFeatures