Abstract: Pseudomonas aeruginosa is a Gram-negative opportunistic pathogen found ubiquitously in the environment. Responsible for considerable human morbidity and mortality, particularly in nosocomial infections and individuals with cystic fibrosis, P. aeruginosa can adapt to surface growth by undergoing swarming motility. In P. aeruginosa, swarming motility is a rapid multicellular movement that occurs on soft surfaces of appropriate viscosity with amino acids as a nitrogen source. Here we tested the small synthetic host defense peptide, innate defense regulator 1018, and found that it inhibited swarming motility at concentrations as low as 0.75 μg/ml, well below the MIC for planktonic cells. A screen of the PA14 transposon insertion mutant library revealed twenty-nine mutants that demonstrated partial tolerance to 1018 under swarming conditions. Two of these mutants, in the genes anr and rhlB (a regulator of anaerobic metabolism and protein involved in rhamnolipid production, respectively), were complemented to restore susceptibility to 1018. RNA-Seq of peptide-treated cells under swarming conditions revealed the dysregulation of 1,190 genes compared to the untreated swarm front, and 67% of these genes were similarly dysregulated at the untreated swarm centre. In contrast, expression of 70 Anr-regulated genes was upregulated by peptide treatment, and 45 genes showed differential or opposite regulation of expression in peptide-treated and swarm centre cells. Many transcriptional regulators required for swarming were dysregulated in peptide-treated cells, indicative of a mechanism by which 1018 may inhibit swarming motility. Overall, this study illustrates a use for peptide 1018 in inhibiting swarming surface motility, an important bacterial adaptation.
Overall design: RNA-Seq of P. aeruginosa inoculated on swarming agar centre and edge cells in the absence or presence of host-defense peptide IDR-1018 (0.75 ug/ml). Thus, three samples with two replicates each.
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