Accueil UNamur > Agenda > Soutenance publique de thèse de doctorat en Sciences biologiques - Adélie Lannoy

Catégorie : défense de thèse
Date : 24/01/2025 14:30 - 24/01/2025 17:30
Lieu : PA02
Orateur(s) : Adélie Lannoy
Organisateur(s) : Xavier De Bolle

The bacterium Brucella abortus is the causal agent of bovine brucellosis. During infection, the bacterium is exposed to a multitude of stresses, mostly unknown, that affect its envelope. Adaptation to these conditions, is essential for these bacteria to survive. However, research on the biogenesis, adaptation and turnover of the envelope in B. abortus remains underrepresented. In this work, we applied a transposon sequencing (Tn-seq) approach in the presence of deoxycholate (DOC) to identify essential genes for bacterial growth in the presence of an envelope stress.

 

The Tn-seq results enabled us to identify and characterise the two-component system (TCS) CenK-CenR. It is established that this TCS plays a role in maintaining cell envelope integrity in related bacteria. We investigated the role of CenR and CenK in B. abortus. The results demonstrated that the cenR deletion resulted in growth defects under DOC stress and in macrophage infections. The inability to obtain a strain either lacking the CenK component or having a constitutively inactive CenR protein indicates that unphosphorylated CenR may exert a bactericidal or bacteriostatic effect on B. abortus. It seems likely that CenR regulates, directly or indirectly, the expression of genes involved in the efflux pump BepDE, thereby conferring resistance to envelope stress on the bacterium.

 

A system in which a fraction of the components is homologous to the Mla pathway, which plays a crucial role in maintaining membrane integrity and lipid transport in Escherichia coli, were also identified by Tn-seq in B. abortus. The deletion of the genes encoding for this system resulted in increased sensitivity to DOC and a decrease in macrophage survival during the early hours of infection, indicating a crutial role in virulence. A homology study and structural predictions using AlphaFold-related programs indicated that the Mla system in B. abortus is a hybrid system that combines proteins homologous to the E. coli Mla and Pqi pathways. This hybrid system has been designated the Mla-Pqi chimeric system (Mpc system). The function of the Mpc system was investigated in order to gain insight into its role in the bacterial cell. Firstly, it was determined that the proteins of the Mpc system form a stable complex which is consistent with its proposed function to bridge both membranes through the formation of a stable. Secondly, the lipid composition of the membranes was investigated. This indicated that in the absence of the Mpc system, there was an altered lipid composition of the OMVs, thereby substantiating the hypothesis that the Mpc plays a role in the transport of lipids between membranes. The discovery of a novel lipid trafficking system enhances the diversity and complexity of known lipid trafficking systems within diderm bacteria.