Type IV-pili dependent motility is co-regulated by PilSR and PilS2R2 two-component systems via distinct pathways in Myxococcus xanthus.

Myxococcus xanthus is an environmental bacterium with two forms of motility. One type, known as social motility, is dependent on extension and retraction of Type-IV pili (T4P) and production of extracellular polysaccharides (EPS). Several signaling systems have been linked to regulation of T4P-dependent motility. In particular, expression of the pilin subunit pilA requires the PilSR two-component signaling system (TCS). A second TCS, PilS2R2, encoded within the same locus that encodes PilSR, has also been linked to M. xanthus T4P-dependent motility. We demonstrate that PilSR and PilS2R2 regulate M. xanthus T4P-dependent motility through distinct pathways. Consistent with known roles of PilSR, our results indicate that the primary function of PilSR is to regulate expression of pilA. In contrast, PilS2 and PilR2 have little to no affect on PilA protein levels. However, deletion of pilR2 resulted in a reduction of assembled pili, significant decreases in EPS production and loss of T4P-dependent motility. Furthermore, the pilR2 mutation led to increased production of outer membrane vesicles (OMV). Collectively, we propose that PilS2R2 is required for proper assembly of T4P and regulation of OMV production, and hypothesize that production of these vesicles is related to M. xanthus motility.