Proteomic analysis reveals modulation of iron homeostasis and oxidative stress response in Pseudomonas aeruginosa PAO1 by curcumin inhibiting quorum sensing regulated virulence factors and biofilm production

Abstract

The aim of the present study was to evaluate the effect of known quorum sensing inhibitors (QSIs) against reference strain Pseudomonas aeruginosa PAO1 and 32 clinical isolates. Among the evaluated QSIs, curcumin effectively inhibited the production of quorum sensing (QS) regulated virulence factors and biofilm production in the reference strain as well as all the clinical isolates. Hence, we sought to unearth the underlying molecular mechanism responsible for QS inhibition by curcumin. Proteomic, mass spectrometric and gene ontology analysis revealed that the differentially regulated proteins are indeed involved in iron acquisition, iron storage, detoxification of reactive oxygen species and synthesis of metabolic intermediates for virulence factor production. In vitro assays also confirmed the alterations in catalase, superoxide dismutase, pyocyanin and pyoverdine production and sensitivity of PAO1 to H2O2 upon curcumin exposure. All these results suggest that curcumin attenuates the QS and biofilm formation by affecting iron homeostasis and oxidative stress response of PAO1. Furthermore, successive exposure of PAO1 to curcumin for 20 successive passages does not affect the efficacy of curcumin to inhibit virulence factor and biofilm production. Hence, it is hypothesized that curcumin inhibits the virulence factor production and biofilm formation without obviously inciting any selection pressure from PAO1.

Biological significance: Most of the well-known QSIs, which are effective against standard strains of P. aeruginosa, are found ineffective against QS regulated virulence determinants of clinical isolates of P. aeruginosa, suggesting the existence of resistance towards QS inhibitors. The non-toxic nature, wide range of pharmacological benefits and the ability to inhibit the QS regulated virulence factors of all the tested clinical isolates of P. aeruginosa in the current study makes curcumin as a potent antagonistic agent against P. aeruginosa. The study on proteomics of P. aeruginosa against curcumin is expected to hold a greater significance in the development of antipseudomonal regimen. The results revealed the ability of curcumin to attenuate the virulence by targeting antioxidant enzymes, iron transport and biosynthesis of metabolic intermediates involved in virulence factors production.

Keywords: Curcumin; Iron homeostasis; Oxidative stress; P. aeruginosa PAO1; Quorum sensing; Quorum sensing inhibition.