Fig. 1: Pneumococcal competence development.
A Competence regulation at the individual cell level. Pre-CSP is matured and exported by ComAB and interacts with the histidine kinase ComD at the cell pole. ComD phosphorylates its cognate response regulator ComE and ComE~P dimers induce the early com regulon, including both comX genes, which encode the alternative sigma factor σX. σX interacts with RNA polymerase to induce late com genes, including dprA. DprA is driven to the cell pole by σX and interacts with ComE~P to promote competence shut-off. B Competence development at the individual cell level. A non-competent cell senses a stress (red contour) and becomes competent. This cell becomes a CSP donor, able to transmit competence to neighbouring cells by cell-to-cell contact. After ~30 min, the cell enters post-competence and is temporarily unable to respond to a competence signal. C Model of populational competence development by propagation. In a growing population, stress and metabolic heterogeneity creates a subpopulation of competent cells able to propagate competence to non-competent neighbours. These cells become competent and can in turn transmit competence, leading to exponential propagation throughout the population. D Model of spontaneous propagation reported by the luciferase transcriptional fusion under the PssbB late competence promoter (PssbB::luc)40,80,81,82,83. A time (XA) is required to produce a cell fraction developing competence in an autocrine mode, which depends on environmental conditions and genotype. The competence development rate (XB) is conditioned by the speed of propagation among non-competent cells, linked to cell density and CSP-retention ability. E Competence propagation visualised by microscopy. Observing binding of fluorescent tDNA to competent cells in different densities of inocula supports the propagation model. Non-competent cells were inoculated in permissive C + Y medium at 8 × 10−3 (high cell density) or 8 × 10−4 (low cell density) to allow visualisation of fluorescent Cy3-DNA bound by competent cells. F Frequency of cells binding Cy3-labelled tDNA throughout the culture from the XA time (30 min, Supplementary Fig. 5A). The rate of increase of tDNA-binding cells is reported with the R2. Thick lines show data range used for rate calculations. Individual data shown representative of triplicate repeats.
