ABSTRACT 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 sulfurreducens and Dichelobacter nodosus implicated 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 pilA with changes in expression in the absence of pilR . Among these were 10 genes inversely dysregulated by loss of pilA versus pilR , even though both pilA and pilR mutants 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, pilSR deletion 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. aeruginosa motility and surface sensing behaviours.
