DegQ and SwrA differentially modulate protease production and flagellar motility in Bacillus subtilis

In Bacillus subtilis, the DegS-DegU two-component system modulates a range of adaptive responses, including extracellular protease production and the flagellar-surface motility called swarming. Two proteins, DegQ and SwrA, are thought to increase the amount of phosphorylated DegU and alter DegU DNA-binding abilities of DegU, respectively. Here we compare the relative contributions of DegQ and SwrA to DegU-related phenotypes in the B. subtilis ancestral strain that is functional for both proteins. We found that DegQ enhances the production of secreted proteases in stationary phase and inhibits swarming motility during exponential growth by a mechanism dependent on both DegS and DegU. Moreover, DegQ-mediated swarming inhibition was due, in part, to the attenuation of transcription levels within the long fla/che operon. SwrA by contrast, activates the promoter of the fla/che operon by a mechanism that depends on DegU but not DegS. Moreover, SwrA inhibits extracellular protease production by inhibiting the expression of DegQ. We conclude that DegQ and SwrA have opposing effects on DegU-dependent phenotypes and do so by different mechanisms. Thus, B. subtilis evolved third-party modulators to expand the conventional two-component system and achieve differential gene expression.