Défense de thèse de doctorat en sciences

Copper resistance in Caulobacter crescentus - Characterization of the Pco operon and of an ABC transporter permease

Jury

De Bolle Xavier (UNamur), président; Matroule Jean-Yves (UNamur), secrétaire; Devos Damien (CADB); Van Houdt Rob (SCK-CEN); Collet Jean-François (UCLouvain).

Résumé

Selective pressure has driven evolution through the ages, forcing organisms to adapt time and again. Organisms developed strategies to face environmental stresses and maintain their fitness. In this context, Caulobacter crescentus, an oligotrophic alphaproteobacterium, has been studied to discover different systems it acquired during evolution to resist against metal stresses.

We characterized the Pco system of C. crescentus and demonstrated that PcoA is a multicopper oxidase, detoxifying the periplasm of the bacterium by oxidizing copper cations. Another protein, PcoB, acts like an efflux pump, exporting copper ions outside the cell. This system would therefore help C. crescentus to regulate both the periplasmic concentration of copper and its toxicity.

Additionally, another system was described. An ABC transporter permease was identified, and we presented data suggesting that this protein would act like a cysteine exporter. Transporting cysteine from the cytoplasm towards the periplasm could help C. crescentus resist to stresses caused by several transition metals, including copper, silver, and cadmium.

The periplasm of Gram-negative bacteria likely represents an important line of defense against exogenous metal stress. Identifying periplasmic resistance systems is therefore of utmost interest to acquire a better understanding of the molecular mechanisms at play in these bacteria, especially since metals are used as bactericide in several domains, such as the medical field or in agriculture.

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