Abstract
ABSTRACT
The
Pseudomonas aeruginosa
type III secretion system (T3SS) is an important virulence determinant used to mute and/or impair host immune defenses. Traditional transposon mutagenesis screens have been instrumental in identifying genes required for T3SS gene expression but our understanding of how those genes orchestrate regulatory control remains incomplete. A comprehensive inventory of the genes involved in the control of T3SS gene expression would help define regulatory mechanisms and provide additional targets for anti-virulence therapeutics. Here, we designed a fluorescently tagged transposon mutagenesis screen (FT-Tn-seq) and identified over 70 new genes important for T3SS gene expression. A role for 31 of those genes was validated using a secondary screen. Several candidate genes were selected for further studies. We demonstrate that deletion of
shaC
, which encodes a sodium-proton antiporter subunit, results in a significant defect in T3SS gene expression. That defect results from a combined effect on
exsA
transcription and ExsA translation. Deletion of
wspF
, a cyclic-di-GMP phosphodiesterase, results in a significant reduction of T3SS expression in strain PAK, but not in PA103. The effect on the T3SS is likely due to elevated levels of c-di-GMP in PAK. Finally, we identified a new sRNA (ivy) that participates in the control of the T3SS. Expression of ivy inhibits T3SS gene expression and requires the RNA-chaperone Hfq for inhibitory activity. Findings from this study will open new research avenues to better understand regulation of T3SS gene expression in
P. aeruginosa
and develop T3SS-specific therapeutic interventions.
IMPORTANCE
Anti-virulence therapeutic approaches are an alternative to conventional antibiotics. Rather than targeting an essential cellular pathway, anti-virulence approaches target a critical virulence function. The
P. aeruginosa
type III secretion system is a critical virulence determinant and validated target for anti-virulence approaches. In principle, any factor/pathway required for T3SS gene expression is a candidate target for therapeutic intervention. To advance our understanding of factors that control T3SS gene expression and broaden the list of potential therapeutic targets we performed a high-throughput screen to comprehensively identify factors required for T3SS gene expression. We now implicate 70 new genes in the control of T3SS gene expression.