Biology subjects

De Bolle, X.

Publications and source records attributed to De Bolle, X..

5 recordsLinked to original sources

bioRxiv2025

Brucella abortus histidine auxotrophs are sensitive to copper

Despite decades of investigation into bacterial pathogens, the conditions met by intracellular bacteria are still unclear. These conditions can include access to nutrients, such as amino acids, and exposure to toxic compounds, like copper. To investigate the ability of Brucella abortus, a facultative intracellular pathogen responsible for a major zoonosis, to cope with copper, we performed a Tn-seq analysis to identify copper-sensitive mutants. Unexpectedly, we realized that classical copper resistance systems (involving CopA and CueO homologs) do not appear to be robustly needed, while histidine and purine biosynthesis pathways are crucial to cope with copper. We show that hisA, hisB, hisC and hisD mutants are auxotrophic for histidine and sensitive to copper. This suggests that the reported attenuation of his mutants in macrophages could be based on auxotrophy or/and copper sensitivity. Therefore, we generated suppressor strains with a restored resistance to copper for hisC, but still auxotrophs for histidine. Our data suggest that this suppression is due to the overproduction of a homolog of OppA, a periplasmic oligopeptide binding protein. Analysis of these suppressors shows that the absence of histidine biosynthesis capacity, and not copper sensitivity, is required for optimal growth of B. abortus in macrophages.

microbiology↗

bioRxiv2025

A subset of type 4 secretion system effectors of Brucella spp. associates to outer membrane vesicles

The establishment of a replicative niche in the hostile environment of the host presents an enormous challenge for pathogens. Intracellular pathogens such as Brucella spp., the Gram-negative causative agents of Brucellosis, must subvert diverse host functions to ensure survival and replication. One of the key adaptations to achieve this is the translocation of effector proteins into host cells via its type 4 secretion system (T4SS), a key virulence factor. But effector identification in Brucella is particularly challenging, as previously identified effectors lack a conserved translocation signal, exhibit variable requirements for translocation, and in some cases appear to be translocated in a T4SS-independent manner. Here, we demonstrate that a subset of previously described T4SS effector proteins associates with outer membrane vesicles (OMVs) in different Brucella species. Most of these effector proteins encode predicted signal peptides for periplasmic export or transmembrane domains. Among them, BspC and VceA carry functional signal peptides that direct their export into the periplasm in a Sec-dependent manner. From the periplasm these proteins are subsequently secreted into the extracellular milieu, likely via the formation and release of OMVs. Our findings provide new insights into protein secretion by Brucella, suggesting that OMVs may represent an alternative secretion pathway to the T4SS.

microbiology↗

bioRxiv2024

A lipid transport Mla Pqi Chimeric system is essential for Brucella abortus survival in macrophages

The envelope of diderm bacteria comprises of an inner membrane (IM) and an outer membrane (OM). Several pathways have been recently identified that facilitate the transport of phospholipids between the two membranes in Escherichia coli, including maintaining OM lipid asymmetry (Mla) and paraquat inducible (Pqi) systems. In this study, we report the identification and the characterization of a complex named Mpc in the intracellular pathogen Brucella abortus. Mpc is conserved in numerous species of Hyphomicrobiales and exhibits homology to both the Mla and Pqi systems. Mpc is essential for bacterial growth under conditions of envelope stress and for survival within macrophages during the early stages of infection. Analyses of protein-protein interactions and structural predictions indicate that the Mpc complex bridges IM to OM. The absence of this system results in an altered lipid composition of the OM vesicles, supporting the fact that 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.

microbiology↗

bioRxiv2022

BNIP3L-mediated mitophagy triggered by Brucella in host cells is required for bacterial egress

The facultative intracellular pathogen Brucella abortus interacts with several organelles of the host cell to reach its replicative niche inside the endoplasmic reticulum. However, little is known about the interplay between the bacteria and the host cell mitochondria. Here, we showed that B. abortus triggers a strong mitochondrial network fragmentation accompanied by mitophagy and the formation of mitochondrial Brucella-containing vacuoles in the late steps of cellular infection. The expression of the mitophagy receptor BNIP3L induced by B. abortus is essential for these events and relies on the iron-dependent stabilization of the hypoxia-inducible factor 1 alpha. Functionally, BNIP3L-mediated mitophagy appears to be advantageous for bacterial exit of the host cell as BNIP3L depletion drastically reduced the number of reinfection events. Altogether, these findings highlight the intricate link between Brucella trafficking and the mitochondria during host cell infection.

microbiology↗

bioRxiv2022

Lipopolysaccharide synthesis and traffic in the envelope of the pathogen Brucella abortus

Lipopolysaccharide is essential for most Gram-negative bacteria as it is a main component of the outer membrane. In the pathogen Brucella abortus, smooth lipopolysaccharide containing the O-antigen is required for virulence. Being part of the Rhizobiales, Brucella spp. display unipolar growth and lipopolysaccharide was shown to be incorporated at the active growth sites, i.e. the new pole and the division site. By localizing proteins involved in the lipopolysaccharide transport across the cell envelope, from the inner to the outer membrane, we show that the lipopolysaccharide incorporation sites are determined by the inner membrane complex of the lipopolysaccharide transport system. Moreover, we identify the main O-antigen ligase of Brucella spp involved in smooth lipopolysaccharide synthesis. Altogether, our data highlight a new layer of spatiotemporal organization of the lipopolysaccharide biosynthesis pathway and identify a new class of bifunctional O-antigen ligases.

microbiology↗