The alternative sigma factor σX mediates competence shut-off at the cell pole in Streptococcus pneumoniae

Abstract

SummaryBacterial competence for genetic transformation is a well-known species-specific differentiation program driving genome plasticity, antibiotic resistance and virulence in many pathogens. How competence regulation is spatiotemporally integrated in the cell is ill-defined. Here, we unraveled the localization dynamics of the key regulators that master the two intertwined transcription waves controlling competence in Streptococcus pneumoniae. The first wave relies on a stress-inducible phosphorelay system, made up of the ComD and ComE proteins, and the second is directed by an alternative sigma factor, σX, which includes in its regulon the DprA protein that turns off competence through interaction with phosphorylated ComE. Remarkably, we found that ComD, σX and DprA stably co-localize at a single cell pole over the competence period. In contrast, ComE assembles into dynamic patches in the cell periphery, colocalizing temporarily with DprA and ComD at the pole. Furthermore, we provide evidence that σX directly conveys DprA polar anchoring. Through this protein targeting function, σX is shown to be actively involved in the timely shut-off of the competence cycle, hence preserving cell fitness. Altogether, this study unveils an unprecedented role for a bacterial transcription σ factor in spatially coordinating the negative feedback loop of its own genetic circuit.