Membrane switching: a colonization pathway for Vibrio cholerae

Socio-economic and scientific context: 

To date, it is estimated that there are 2.9 million cases of cholera each year, resulting in 95,000 deaths. In an attempt to remedy this situation, the WHO has set an ambitious target: to eliminate cholera from high-risk areas by 2030. One of the reasons for the success of Vibrio cholerae, the causative agent of cholera, is that this bacterium can precisely regulate the expression of its genes to thrive in nutrient-poor environments, and more particularly in phosphorus-poor environments. To survive inorganic phosphate (Pi) limitation, V. cholerae regulates genes belonging to the Pho regulon and remodels its membrane using the PhoBR two-component regulatory system. While the vast majority of marine waters are limited by essential nutrients such as Pi, coastal areas are subject to waves of Pi where V. cholerae often persists.

Assumptions and questions: 

Previous studies have shown that V. cholerae and other intestinal pathogenic bacteria that are unable to 'sense' low phosphate concentration in the intestine are less efficient at colonising it, an environment hitherto known to be rich in nutrients. Overall, a mechanistic understanding of the physiological trade-offs of V. cholerae membrane remodeling in response to Pi limitation remains to be investigated. The PhD student will focus on understanding the potential key role of the PhoBR system and membrane remodelling in the adaptation and persistence of V. cholerae in marine environments and during its interaction with heterotrophic protists which may lead to a transfer within the trophic chain.

The main steps of the thesis and scientific procedure:

To answer this question, the PhD student will have to :

i- Provide a complete picture of V. cholerae membrane remodelling in response to phosphate stress using ‘omics’ approaches such as lipidomics, glycomics and proteomics. This will allow us to generate mutants in the membrane remodelling pathway to identify the genes involved in this switching of the membrane.

ii- determine the lifestyle of Vibrio cholerae in marine environment with respect to phosphate availability using wild type strains and mutants in membrane remodelling pathway. We will compare the ability to build biofilms quantitively and qualitatively and the motility capacities of these strains in a defined low and high Pi media.

iii- Identify the risk of transfer within the trophic chain using predatory heterotrophic protists. To check whether the ability to remodel the membrane is part of the strategy used by V. cholerae to avoid predation by protozoa, we will test mutants in the membrane remodelling pathway (unable to remodel their membrane) against different strains of heterotrophic protists.

Methodological and technical approaches considered:

This thesis project will enable the student to learn all the techniques associated with lab-based microbiology and host-bacteria interactions. In addition, molecular biology techniques involving the creation of mutants, bioraporters and the biochemical analysis of the various biomolecules produced by these bacteria will also be used during this project, as will the use of high-resolution microscopy (confocal, electron).

If you have any questions, please contact:

Richard Guillonneau (richard.guillonneau(at)univ-nantes.fr)

The thesis will be based at the US2B laboratory at Nantes University.

Scientific and technical skills required by the candidate:

Given the objectives set, the candidate should have a good knowledge of microbiology, cell biology and host-bacteria interactions, as well as some knowledge of biochemistry. From a technical point of view, he/she should also be interested in molecular biology tools, biochemical analyses and microscopy. V. cholerae is a pathogenic bacterium that will be handled in a cat-2 laboratory, so good organisation and strict compliance with hygiene and safety rules will be necessary.

Finally, the candidate should have a general interest in the transfer and persistence of pathogens in the environment