A Quorum Sensing Regulated Small Volatile Molecule Reduces Acute Virulence and Promotes Chronic Infection Phenotypes

Abstract

A significant number of environmental microorganisms can cause serious, even fatal, acute and chronic infections in humans. The severity and outcome of each type of infection depends on the expression of specific bacterial phenotypes controlled by complex regulatory networks that sense and respond to the host environment. Although bacterial signals that contribute to a successful acute infection have been identified in a number of pathogens, the signals that mediate the onset and establishment of chronic infections have yet to be discovered. We identified a volatile, low molecular weight molecule, 2-amino acetophenone (2-AA), produced by the opportunistic human pathogen Pseudomonas aeruginosa that reduces bacterial virulence in vivo in flies and in an acute mouse infection model. 2-AA modulates the activity of the virulence regulator MvfR (multiple virulence factor regulator) via a negative feedback loop and it promotes the emergence of P. aeruginosa phenotypes that likely promote chronic lung infections, including accumulation of lasR mutants, long-term survival at stationary phase, and persistence in a Drosophila infection model. We report for the first time the existence of a quorum sensing (QS) regulated volatile molecule that induces bistability phenotype by stochastically silencing acute virulence functions in P. aeruginosa. We propose that 2-AA mediates changes in a subpopulation of cells that facilitate the exploitation of dynamic host environments and promote gene expression changes that favor chronic infections.

The bacterial metabolite 2-aminoacetophenone promotes association of pathogenic bacteria with flies

“…On the top of the yeast paste in each trap, we added either 500 ml of pqsA-mutant P.a or 500 ml of pqsBC-mutant P.a LB medium culture at OD 600 ¼ 5, grown in the presence of 10 mg ml À 1 2-Heptyl-3-hydroxy-4(1H)-quinolone (Sigma-Aldrich Cat.#94398). Under these bacterial culturing conditions the pqsA mutant produces wt levels of 2AA, while the pqsBC strain does not produce any detectable 2AA in a liquid LB medium, as previously determined by liquid chromatography/mass spectroscopy analysis 18 . While 2AA is seemingly the only compound not produced by the pqsA versus the pqsBC mutant, there might be additional differentially produced compounds undetected by our previous liquid chromatography/mass spectroscopy analysis 18 .…”

“…2AA is a secondary metabolite of P.a, important in controlling bacterial virulence 18 . Virulence reduction has been correlated with the ability of P.a to chronically colonize humans and animals 18,28 .…”

“…Virulence reduction has been correlated with the ability of P.a to chronically colonize humans and animals 18,28 . Chronicity is presumably an adaptation that enables the bacteria to live, grow and avoid killing the host for longer periods of time.…”

“…aeruginosa stocks. Wt P.a (PA14 strain) and gene deletion mutants pqsA and pqsBC (PA14 strain derivatives) were obtained from the Laurence Rahme lab (Harvard University) and described in Keserwani et al 18 P.a has been previously shown to express 2AA at low micromolar to milimolar concentrations depending on the culture media and the microbial strain used 19 .…”

“…2AA is a single benzene ring aromatic compound with a 'grape-like' odour that promotes chronic P.a infection phenotypes, including long-term bacterial survival at a stationary phase and a reduction in bacterial virulence in various hosts 18 . We assess the ability of 2AA to attract flies and to facilitate intestinal colonization by P.a upon 2AA ingestion.…”