Pseudomonas aeruginosa type IV minor pilins and PilY1 regulate virulence by modulating FimS-AlgR activity

Abstract

Type IV pili are expressed by a wide range of prokaryotes, including the opportunistic pathogen Pseudomonas aeruginosa. These flexible fibres mediate twitching motility, biofilm maturation, surface adhesion, and virulence. The pilus is composed mainly of major pilin subunits while the low abundance minor pilins FimU-PilVWXE and the putative adhesin PilY1 prime pilus assembly and are proposed to form the pilus tip. The minor pilins and PilY1 are encoded in an operon that is positively regulated by the FimS-AlgR two-component system. Independent of pilus assembly, PilY1 was proposed to be a mechanosensory component that—in conjunction with minor pilins—triggers up-regulation of acute virulence phenotypes upon surface attachment. Here, we investigated the link between the minor pilins/PilY1 and virulence. pilW, pilX, and pilY1 mutants had reduced virulence towards Caenorhabditis elegans relative to wild type or a major pilin mutant, implying a role in pathogenicity that is independent of pilus assembly. We hypothesized that loss of specific minor pilins relieves feedback inhibition on FimS-AlgR, increasing transcription of the AlgR regulon and delaying C. elegans killing. Reporter assays confirmed that FimS-AlgR were required for increased expression of the minor pilin operon upon loss of select minor pilins. Overexpression of AlgR or its hyperactivation via a phosphomimetic mutation reduced virulence, and the virulence defects of pilW, pilX, and pilY1 mutants required FimS-AlgR expression and activation. We propose that PilY1 and the minor pilins inhibit their own expression, and that loss of these proteins leads to FimS-mediated activation of AlgR that suppresses expression of acute-phase virulence factors and delays killing. This mechanism could contribute to adaptation of P. aeruginosa in chronic lung infections, as mutations in the minor pilin operon result in the loss of piliation and increased expression of AlgR-dependent virulence factors–such as alginate–that are characteristic of such infections.

The Xanthomonas oryzae pv. oryzae type IV pilus alignment subcomplex protein PilN contributes to regulation of bacterial surface‐associated behaviours and T3SS system

“…It is generally thought that a mucoid strain would produce more EPS (Marko et al, 2018), and this is in agreement with our results that the mucoid pilN mutant produced enhanced EPS compared to the wild-type strain. In addition, increased biofilm formation was observed in the pilN mutant, consistent with previous reports showing that EPS production has a positive correlation with biofilm formation in Xanthomonas species (Buttner and Bonas, 2010).…”

PilY1 and minor pilins form a complex priming the type IVa pilus in Myxococcus xanthus

“…The major pilin and minor pilins interact. To address whether the mature forms of the major pilin PilA and minor pilins of cluster_3, i.e., pilins without the type III signal peptide, interact, we used the Bacterial Two-Hybrid (BACTH) system as previously described to detect interactions between minor and major pilins of T4aP systems and the pseudopilins of type II secretion systems (T2SS) 10,[26][27][28][29][30][31] . To this end, the T18 and T25 fragments of the adenylate cyclase were fused to the N-terminus of the full-length mature pilins.…”

The RpoN2‐PilRX regulatory system governs type IV pilus gene transcription and is required for bacterial motility and virulence in Xanthomonas oryzae pv. oryzae

“…Minor pilins encoded by fimTX‐pilVX/WX/XX/EX and a nonpilin protein encoded by pilYX are required for T4P biogenesis and therefore T4P‐mediated motility and virulence (Russell and Darzins, ; Alm et al , ; Alm and Mattick, ). Interestingly, an increasing number of studies have shown that these proteins have roles in virulence independent on functional pili (Bohn et al , ; Feinbaum et al , ; Marko et al , ). These results indicate that RpoN2‐PilRX plays an important role in pilus‐dependent or pilus‐independent biological functions by directly or indirectly regulating T4P genes in Xoo.…”