Surface sensing triggers a broad‐spectrum antimicrobial response in Pseudomonas aeruginosa

Abstract

Summary Interspecies bacterial competition may occur via cell‐associated or secreted determinants and is key to successful niche colonization. We previously evolved Pseudomonas aeruginosa in the presence of Staphylococcus aureus and identified mutations in the Wsp surface‐sensing signalling system. Surprisingly, a ΔwspF mutant, characterized by increased c‐di‐GMP levels and biofilm formation capacity, showed potent killing activity towards S. aureus in its culture supernatant. Here, we used an unbiased metabolomic analysis of culture supernatants to identify rhamnolipids, alkyl quinoline N‐oxides and two siderophores as members of four chemical clusters, which were more abundant in the ΔwspF mutant supernatants. Killing activities were quorum‐sensing controlled but independent of c‐di‐GMP levels. Based on the metabolomic analysis, we formulated a synthetic cocktail of four compounds, showing broad‐spectrum anti‐bacterial killing, including both Gram‐positive and Gram‐negative bacteria. The combination of quorum‐sensing‐controlled killing and Wsp‐system mediated biofilm formation endows P. aeruginosa with capacities essential for niche establishment and host colonization.

Pseudomonas aeruginosa rhamnolipid micelles deliver toxic metabolites and antibiotics into Staphylococcus aureus

“…We have previously shown that supernatants of a wspF mutant of P. aeruginosa contain elevated concentrations of several secondary metabolites, including RLPs. RLPs were an essential ingredient of a synthetic cocktail, including the siderophores pyoverdine and pyochelin, as well as the alkylquinoline 2-heptyl-4-hydroxyquinoline-N-oxide (HQNO), able to cause a 5-log reduction of viable counts of S. aureus ( Gdaniec et al., 2020 ) within 24 h. We wondered whether the RLPs concentration previously measured at 300–400 μg/mL in the wspF mutant supernatant ( Gdaniec et al., 2020 ) would be sufficient to form micelles. We therefore analyzed by electron microscopy the supernatants of P. aeruginosa PA14Δ wspF and an isogenic Δ wspFΔrhlA mutant, deficient in RLP production.…”

“…To further substantiate the specific role of RLPs in S. aureus killing, we supplemented the ultra-S and 15x ultra-P of the Δ wspF Δ rhlA mutant with commercial RLPs. Our previous metabolomic analysis of Δ wspF supernatant had shown a large diversity of RLPs, dominated by the C 10 -C 10 di-RLP species ( Gdaniec et al., 2020 ). We therefore used a mix of purified mono- and di-RLPs ( Figure 2 E), but also C 10 -C 10 ( Figure 2 F) or C 12 -C 12 mono-RLPs ( Figure 2 G) alone for the supplementation experiments.…”

“…As RLPs are essential for killing of S. aureus in combination with other metabolites present in the P. aeruginosa Δ wspF mutant supernatants ( Gdaniec et al., 2020 ), we investigated whether RLP micelles might potentiate the effect of antibiotics. We tested the effect of azithromycin, novobiocin, rifampicin, nalidixic acid, ciprofloxacin, ampicillin, and sulfamethoxazole on S. aureus in the presence/absence of RLPs, as representative members of the main antibiotic classes.…”

“…We have recently defined an antimicrobial cocktail consisting of proteins and several metabolites secreted by P. aeruginosa , which showed broad-spectrum killing activity against both Gram-positive and Gram-negative bacterial species ( Gdaniec et al., 2020 ). An essential component of this cocktail was rhamnolipids (RLPs), which belong to the chemically diverse group of glycolipids.…”

Characterization of Pseudomonas aeruginosa Quorum Sensing Inhibitors from the Endophyte Lasiodiplodia venezuelensis and Evaluation of Their Antivirulence Effects by Metabolomics

“…For this, a similar UHPLC HRMS/MS profiling approach as the one used for the analysis of the composition of the fungal strain A02 was applied. We recently used this strategy to identify and compare secreted bacterial compounds between wild type and mutants of P. aeruginosa [ 62 ]. Indeed, it has been demonstrated that about one third of the metabolome of P. aeruginosa was linked to QS, with secondary metabolite levels modulated by a lack of QS signaling molecules [ 63 ], and that clinical strains with different virulence phenotypes also had different metabolic profiles.…”