The Flagellar Transcriptional Regulator FtcR Controls 16M Biofilm Formation via a -Mediated Pathway in Response to Hyperosmotic Stress.

The expression of flagellar proteins in species likely evolved through genetic transference from other microorganisms, and contributed to virulence, adaptability, and biofilm formation. Despite significant progress in defining the molecular mechanisms behind flagellar gene expression, the genetic program controlling biofilm formation remains unclear. The flagellar transcriptional factor (FtcR) is a master regulator of the flagellar system's expression, and is critical for 16M's flagellar biogenesis and virulence. Here, we demonstrate that FtcR mediates biofilm formation under hyperosmotic stress. Chromatin immunoprecipitation with next-generation sequencing for FtcR and RNA sequencing of -mutant and wild-type strains revealed a core set of FtcR target genes. We identified a novel FtcR-binding site in the promoter region of the osmotic-stress-response regulator gene , which is important for the survival of 16M under hyperosmotic stress. Strikingly, this site autoregulates its expression to benefit biofilm bacteria's survival under hyperosmotic stress. Moreover, biofilm reduction in mutants is independent of the flagellar target gene . Collectively, our study provides new insights into the extent and functionality of flagellar-related transcriptional networks in biofilm formation, and presents phenotypic and evolutionary adaptations that alter the regulation of 16M to confer increased tolerance to hyperosmotic stress.