Stator remodeling mechanism ofBacillus subtilisflagellar motor during biofilm development

Bacillus subtilis possesses two distinct types of stator protein complexes for the flagellar motor: H + -type MotAB and Na + -type MotPS. The MotPS complex is used when both the external Na + concentration and viscosity are high. Because deletion of the motPS genes does not affect swimming motility of cells, a physiological role of MotPS-dependent motility remains unclear. Here, we report that the MotPS stator complex is required for efficient biofilm maturation. Depletion of the MotPS complex did not cause a significant delay in the initiation of biofilm formation but reduced the number of viable cells in the biofilm. The MotAB stator units were efficiently replaced by the MotPS complexes with an increase in the viscosity of the environments. Therefore, we propose that MotPS-dependent motility of motile cells in the biofilm structure is required to efficiently keep the bacterial society in the biofilm healthy.