Bacterial cell–cell signalling, or quorum sensing, is characterized by the secretion and groupwide detection of small diffusible signal molecules called autoinducers. This mechanism allows cells to coordinate their behaviour in a density-dependent manner. A quorum-sensing cell may directly respond to the autoinducers it produces in a cell-autonomous and quorum-independent manner, but the strength of this self-sensing effect and its impact on bacterial physiology are unclear. Here, we explore the existence and impact of self-sensing in the Bacillus subtilis ComQXP and Rap-Phr quorum-sensing systems. By comparing the quorum-sensing response of autoinducer-secreting and non-secreting cells in co-culture, we find that secreting cells consistently show a stronger response than non-secreting cells. Combining genetic and quantitative analyses, we demonstrate this effect to be a direct result of self-sensing and rule out an indirect regulatory effect of the autoinducer production genes on response sensitivity. In addition, self-sensing in the ComQXP system affects persistence to antibiotic treatment. Together, these findings indicate the existence of self-sensing in the two most common designs of quorum-sensing systems of Gram-positive bacteria.
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This work was supported by European Research Council grants 281301 and 724805. The authors thank R.D. Oshri and N. Antonovsky for comments and N. Sigal for help with qPCR.
Electronic supplementary material
Supplementary Figures 1–10, Supplementary Tables 1 and 2, Supplementary Discussion, Supplementary References.
Supplementary Dataset 1Description: Zip file including 11 excel files. These files include all data used in the manuscript figures and supplementary figures. File name corresponds to the figure numbers whose data it includes.