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Pseudomonas aeruginosa is a very resistant opportunistic pathogen, for which it is critical to find new therapies. This bacterium easily adapts to its environment, through its large genome and proportion of regulators allowing a very fine regulation of its genes. The cell wall is the first barrier in contact with environment, and therefore represents a very important place ofexchange. The cell wall thus represents an interesting potential therapeutic target. SigX is an extracytoplasmic function sigma factor, responding to cell wall stresses detected by the bacterium, but the precise stimulus remains to discover. This sigma factor could be part of a new atypical signal transduction system that could couple SigX with a mechanosensitive channel. This work has led to the discovery of three new sigX activating conditions, which are Pf4 phage infection, loss of the CmpX mechanosensitive channel, and cold shock. These conditions seem to cause strong perturbations and an increase in membrane stiffness that could be the activating stimulus of SigX. This work has led to a better understanding of the activating condition of SigX, and to the clarification of the cellular and regulatory functions of the SigXCfrX-CmpX system members, highlighting the involvement of a mechanosensitive channel in the physiology of Pseudomonas aeruginosa., Pseudomonas aeruginosa est un pathogène opportuniste très résistant, pour lequel il est critique de trouver de nouvelles thérapies. Cette bactérie s’adapte facilement à son environnement grâce à son grand génome et à sa grande proportion de régulateurs permettant une régulation très fine de ses gènes. L’enveloppe est la première barrière au contact direct de l’environnement, et est un lieu d’échanges très important entre ce dernier et la bactérie. L’enveloppe représente donc une cible thérapeutique potentielle intéressante. SigX est un facteur sigma à fonction extracytoplasmique, permettant de répondre à des situations de stress d’enveloppe détectées par la bactérie, mais dont le stimulus exact reste à déterminer. Ce facteur sigma pourrait faire partie d’un nouveau système de transduction atypique du signal, qui pourrait coupler SigX à un canal mécanosensible. Ces travaux ont mené à la découverte de trois nouvelles conditions activatrices de SigX, l’infection par des phages Pf4, la perte du canal mécanosensible CmpX, et le choc froid. Ces dernières semblent provoquer de fortes perturbations et une augmentation de la rigidité membranaire qui pourrait être le stimulus activateur de SigX. Ces travaux ont permis d’étoffer les connaissances et de se rapprocher de la condition activatrice de SigX, et de préciser les fonctions cellulaires et régulatrices des membres du système SigX-CfrX-CmpX, mettant en exergue l’implication d’un canal mécanosensible dans la physiologie de Pseudomonas aeruginosa.

International audience; Pseudomonas aeruginosa is a gram-negative pathogen of great concern in immune-compromised individuals and the major cause of mortality in cystic fibrosis patients. Its pathogenicity lies in the production of myriad of virulence factors such as phenazines (pyocyanin), exoenzymes (elastase B), siderophores, exopolysaccharides and surfactants (rhamnolipids), among others. In addition, P. aeruginosa forms aggregated communities of cells encased in an extracellular matrix known as biofilms making it resistant to most of the available antibiotic agents. Following the discovery of quorum sensing (QS) system, involved in the regulation of virulence factors, resistance, and biofilm formation in P. aeruginosa, anti-virulence therapy has been adopted as a novel approach to combat the multi-drug resistance bacteria. In view of this, there has been extensive search in natural products for chemotherapeutic compounds that can override the virulence factors and their regulation by the QS communication system without affecting bacterial growth. Since plants are known repositories of secondary metabolites with chemical defense systems against environmental microbes, in this study, extract from Mulinum crasiifolium Phil. of Apiaceae family, was investigated for anti-virulence factors and anti-biofilm activities against P. aeruginosa. To perform virulence factors quantification assays, P. aeruginosa was grown in absence or presence of M. crasiifolium extract (McE) at different concentrations. The obtained results showed that McE hinder significantly pyocyanin pigment production without disturbing bacterial growth. Moreover, this anti-pyocyanin activity was found to be dose-dependent. The results demonstrated also that McE decreased elastase and rhamnolipid production. All of these effects seem to be associated to the inhibition of QS molecules production and the alteration of membrane fluidity. As a future work, we intend to evaluate the effects of the McE on in vivo models and further fractionate the McE and identify the bioactive compounds and their mechanisms of action.

International audience

International audience

International audience