MEXT REGULATION

Dissecting the role of a novel transcriptional regulator in microbial-host interactomes

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 Obiettivo del progetto (Objective)

'Pseudomonas aeruginosa is a versatile bacterium that can inhabit many environments. In its natural environments, Pseudomonas predominantly grows in organized communities called biofilms. Growth as a biofilm is also an important requirement for the colonization of human tissues. For instance, P. aeruginosa grows as a biofilm in the lungs of cystic fibrosis (CF) patients. Previously, it has been shown that nfxC-phenotypic isolates of P. aeruginosa associated with decreased early attachment - the first phase of biofilm formation. This chloramphenicol resistant nfxC-phenotype is thought to be caused by the activation of a LysR-type transcriptional regulator, MexT, which regulates the expression of the MexEF-oprN efflux-system. Recently, we have shown that this biofilm phenotype is a result of the activation of MexT in a MexEF-oprN independent manner (Tian et al., 2009). To further establish the role of MexT in biofilm formation, preliminary flow-cell biofilm experiments have been performed. Analysis of the biofilm structure showed that biofilms of cells overexpressing MexT contain a higher microcolony-density with smaller average size as compared to control cells. These differences were independent of the MexEF-oprN efflux system. This project aims to dissect how MexT modulates biofilm formation. Several potential candidate genes have been identified using a transcriptome approach of cells overexpressing MexT, which will be subject to further evaluation (Tian et al., 2009). To further establish the role of MexT on virulence phenotypes, eukaryotic cell lines, as well as a ‘state of the art’ infection model that uses zebrafish embryos will be used. This study may identify potential targets for the modulation of biofilm formation. In the long term, these targets may provide new strategies to develop drugs that reduce the ability of Pseudomonas to form biofilms, thereby increasing the chance of successful antibiotic treatment therapies.'

Introduzione (Teaser)

Pseudomonas aeruginosa is an opportunistic pathogen that is usually encountered in hospitalised patients or individuals suffering from cystic fibrosis. Understanding the molecular mechanisms of bacterial spread and antibiotic resistance would have significant clinical implications.

Descrizione progetto (Article)

P. aeruginosa is inherently multi-drug resistant which hampers treatment efficacy of antibiotics and other antimicrobial agents. This resistance has been attributed to the bacterial membrane which carries specialised efflux pumps, rendering it impermeable to most drugs.

Clinical isolates of P. aeruginosa have been found to express high levels of such efflux systems (MexEF-OprN), which also facilitate bacterial colonisation and spread within the host. Understanding how these pumps regulate key bacterial properties was the subject of the EU-funded 'Dissecting the role of a novel transcriptional regulator in microbial-host interactomes.' (MEXT REGULATION) project.

The MexEF-OprN efflux system is transcriptionally regulated by MexT. Scientists therefore concentrated their efforts on delineating the role of this protein in bacteria survival and spread. They obtained bacteria overexpressing MexT and identified the MexT-regulated gene, PA4353, as a key determinant of biofilm formation and growth.

Interestingly, MexT seemed to additionally impact the virulence of P. aeruginosa in the wax moth model. Overexpression of this master regulator significantly reduced the levels of P. aeruginosa required to kill the wax moth.

Overall, the work by the MEXT REGULATION study established MexT as an important factor of P. aeruginosa virulence. P. aeruginosa is the predominant cause of morbidity in cystic fibrosis patients. Elimination of MexT from the pathogen could reduce its virulence and therefore provide a therapeutic target.