Motility is an important virulence trait for many bacterial pathogens, allowing them to position themselves in appropriate locations at appropriate times. Motility structures - pili and flagella - are also involved in sensing surface contact, which modulates pathogenicity. In
Pseudomonas aeruginosa, the PilS-PilR two-component system (TCS) regulates expression of the type IV pilus (T4P) major subunit PilA, while biosynthesis of the single polar flagellum is regulated by a hierarchical system that includes the FleSR TCS. Previous studies in Geobacter sulfurreducensand Dichelobacter nodosusimplicated PilR in regulation of non-T4P-related genes, including some involved in flagellar biosynthesis. Here we used RNAseq analysis to identify genes in addition to pilAwith changes in expression in the absence of pilR. Among these were 10 genes inversely dysregulated by loss of pilAversus pilR, even though both pilAand pilRmutants lack T4P and pilus-related phenotypes. The products of those genes - many of which were hypothetical - may be important for virulence and surface-associated behaviours, as mutants had altered swarming motility, biofilm formation, type VI secretion, and pathogenicity in a nematode model. Further, the PilSR TCS positively regulated transcription of fleSR, and thus many genes in the FleSR regulon. As a result, pilSRdeletion mutants had defects in swimming motility that were independent of the loss of PilA. Together these data suggest that in addition to controlling T4P expression, PilSR have a broader role in the regulation of P. aeruginosamotility and surface sensing behaviours.