Sigma B regulated motility and chemotaxis in Bacillus cereus

This study describes an alternative role of the general stress response (GSR) regulated by Sigma B, via the two-component system RsbKY, which is methylated via RsbM, in motility regulation for the peritrichously flagellated, motile, foodborne pathogen Bacillus cereus. Using a set of Sigma B-related mutants, we found reduced surface spreading on low-agar plates for all mutants compared to the WT of B. cereus ATCC 14579. The GSR mutants still contained flagella similar to WT in the samples taken from the edge of colonies with reduced surface spreading. Using cell trajectory analysis of selected mutants and WT, we found that the Sigma B-controlled Hpr-like phosphocarrier bc1009 mutant had a reduced duration of the run phase, resulting in an overall lower persistence and coverage of the surface area over a given time. Indeed, prolonged incubation of low-agar 'swimming' plates resulted in full coverage by all GSR mutants, indicating functional motility, but reduced efficiency. Proteome analysis of samples from low-agar plates showed overall lower expression levels of motility-related proteins and, in particular, significantly lower values for proteins related to the C-ring, involved in the regulation of the run-and-tumble motion of bacteria. The bc1009 mutant showed an additional downregulation of a subset of methyl-accepting chemotaxis proteins, involved in the activation of the key chemotaxis regulators CheA and CheY. We propose a new chemotaxis model, in which CheA and CheY are still key regulators, but an additional regulatory role on the run-and-tumble motion is proposed for the Sigma B-regulated Hpr-like protein Bc1009 via the unique two-component system RsbKY.