A Duo of Potassium-Responsive Histidine Kinases Govern the Multicellular Destiny of Bacillus subtilis

Multicellular biofilm formation and surface motility are bacterial behaviors considered mutually exclusive. How- ever, the basic decision to move over or stay attached to a surface is poorly understood. Here, we discover that in Bacillus subti- lis, the key root biofilm-controlling transcription factor Spo0A~Pi(phosphorylated Spo0A) governs theflagellum-independent mechanism of social sliding motility. A Spo0A-deficient strain was totally unable to slide and colonize plant roots, evidencing the important role that sliding might play in natural settings. Microarray experiments plus subsequent genetic characterization showed that the machineries of sliding and biofilm formation share the same main components (i.e., surfactin, the hydrophobin BslA, exopolysaccharide, and de novo-formed fatty acids). Sliding proficiency was transduced by the Spo0A-phosphorelay histi- dine kinases KinB and KinC. We discovered that potassium, a previously known inhibitor of KinC-dependent biofilm forma- tion, is the specific sliding-activating signal through a thus-far-unnoticed cytosolic domain of KinB, which resembles the selec- tivityfilter sequence of potassium channels. The differential expression of the Spo0A~PireporterabrBgene and the different levels of the constitutively active form of Spo0A, Sad67, in spo0Acells grown in optimized media that simultaneously stimulate motile and sessile behaviors uncover the spatiotemporal response of KinB and KinC to potassium and the gradual increase in Spo0A~P ithat orchestrates the sequential activation of sliding, followed by sessile biofilm formation andfinally sporulation in the same population. Overall, these results provide insights into how multicellular behaviors formerly believed to be antagonis- tic are coordinately activated in benefit of the bacterium and its interaction with the host. IMPORTANCE Alternation between motile and sessile behaviors is central to bacterial adaptation, survival, and colonization. However, how is the collective decision to move over or stay attached to a surface controlled? Here, we use the model plant- beneficial bacterium Bacillus subtilis to answer this question. Remarkably, we discover that sessile biofilm formation and social sliding motility share the same structural components and the Spo0A regulatory network via sensor kinases, KinB and KinC. Potassium, an inhibitor of KinC-dependent biofilm formation, triggers sliding via a potassium-perceiving cytosolic domain of KinB that resembles the selectivityfilter of potassium channels. The spatiotemporal response of these kinases to variable potas- sium levels and the gradual increase in Spo0A~Pilevels that orchestrates the activation of sliding before biofilm formation shed light on how multicellular behaviors formerly believed to be antagonistic work together to benefit the populationfitness.