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

Abstract

Multicellular biofilm formation and surface motility are bacterial behaviors considered mutually exclusive. However, the basic decision to move over or stay attached to a surface is poorly understood. Here, we discover that in Bacillus subtilis, the key root biofilm-controlling transcription factor Spo0A~Pi (phosphorylated Spo0A) governs the flagellum-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 histidine kinases KinB and KinC. We discovered that potassium, a previously known inhibitor of KinC-dependent biofilm formation, is the specific sliding-activating signal through a thus-far-unnoticed cytosolic domain of KinB, which resembles the selectivity filter sequence of potassium channels. The differential expression of the Spo0A~Pi reporter abrB gene and the different levels of the constitutively active form of Spo0A, Sad67, in Δspo0A cells 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~Pi that orchestrates the sequential activation of sliding, followed by sessile biofilm formation and finally sporulation in the same population. Overall, these results provide insights into how multicellular behaviors formerly believed to be antagonistic are coordinately activated in benefit of the bacterium and its interaction with the host.

Monitoring Spatial Segregation in Surface Colonizing Microbial Populations

“…In the absence of flagellum, certain bacterial strains are able to move over semi-solid medium via sliding, i.e. growth dependent population expansion facilitated by exopolysaccharide matrix and other secreted hydrophobin compounds [22][23][24] . Finally, bacteria which are capable of biofilm development form architecturally complex colonies on hard agar medium (1.2-2%) 14,17,25 .…”

Transcriptional regulation of adhesive properties of Bacillus subtilis to extracellular matrix proteins through the fibronectin‐binding protein YloA

“…; Gottig et al ., ; Chu et al ., ). Low levels of Spo0A∼P repress abrB expression (Strauch et al ., ; Grau et al ., ) and intermediate levels of Spo0A∼P induce sinI , which encodes for an inhibitor of SinR activity (SinI protein) (Shafikhani et al ., ; Gottig et al ., ). By contrast, in the absence of Spo0A activity, AbrB and SinR are upregulated (Strauch et al ., ; Shafikhani et al ., ; Gottig et al ., ; Chu et al ., ).…”

“…Effectively, the abrB transcript was detectable only at the onset of exponential growth, and AbrB protein levels diminished continuously towards the end of exponential phase because increasing amounts of Spo0A∼P repress its transcription. Thus, AbrB‐mediated regulation is progressively attenuated towards the transition phase (Strauch et al ., ; Strauch, ; Grau et al ., ). Our β‐galactosidase assays in different B. subtilis genetic backgrounds strongly suggested an AbrB‐regulated yloA expression pattern and showed that the adherence deficiency of Spo0A∼P‐deficient cells was due to overexpression of the global regulator AbrB (Fig.…”

Bacillus subtilis, the model Gram‐positive bacterium: 20 years of annotation refinement

“…As a case in point, among many other examples, YfmS, a chemotaxis sensory transducer recognizing a still unknown substrate is involved in the colonization of Arabidopsis thaliana roots (Allard‐Massicotte et al ., 2017). Last, the Spo0A protein that controls the fate of cells as vegetative, spores or biofilm‐forming cells, is key to root colonization (Grau et al ., 2015). Strain 168, however, is mutated in several genes that would compromise its occupation of this natural biotope: it requires tryptophan for growth because trpC has been inactivated by a frameshift, and, in the same way, it cannot properly colonize roots because of inactivation of gene sfpA for example.…”

“…Remarkably, swarming appears to be dependent on a modification of translation factor EF‐P by a 5‐aminopentanol group, as swarming is defective in the absence of EfpI(YmfI) that reduces aminopentanone to aminopentanol (Hummels et al ., 2017). In addition, B. subtilis , even when devoid of appendages, is capable of sliding on surfaces (Kovacs et al ., 2017), dependent on the presence of surfactin (defective in strain 168, due to pseudogene sfpA ) and of exopolysaccharides discussed below, that, interestingly, generate osmotic pressure in the extracellular space (Grau et al ., 2015). …”