SwrA

SwrA is a regulatory protein encoded by the swrA gene in Bacillus subtilis and related Bacillus species. It functions as a pleiotropic transcriptional regulator that influences several surface-associated traits, most notably swarming motility and the production of extracellular enzymes. In laboratory strains, SwrA promotes expression of genes required for swarming on semi-solid surfaces and modulates the activity of other regulators within the network, particularly in concert with the DegS-DegU two-component system.

SwrA interacts with components of the DegS-DegU signaling pathway, and its regulatory effects are linked to the phosphorylation state of DegU (DegU~P). Through these interactions, SwrA helps coordinate gene expression in response to population density and environmental cues. SwrA also associates with SwrB, a membrane-associated factor implicated in the SwrA regulatory module, reinforcing its role in surface-related multicellular behavior.

Phenotypically, loss of SwrA function often results in reduced swarming on semi-solid media and altered patterns of extracellular enzyme production, reflecting its role in coordinating social motility and surface-associated metabolism. Conversely, SwrA activity supports the development of coordinated colony behavior and colony organization in certain Bacillus strains.

SwrA’s presence and function are influenced by strain background and environmental conditions. Homologs are found across Bacillus species, suggesting a conserved role in regulating surface-associated and multicellular behaviors in this genus.