Biology subjects

AUDRAIN, B.

Publications and source records attributed to AUDRAIN, B..

4 recordsLinked to original sources

bioRxiv2026

Global analysis of trimeric autotransporters reveals phylogenetically restricted secretion mechanism adaptations

Autotransporters are important diderm bacterial cell-surface proteins and are virulence factors enabling surface attachment and adhesion to other bacteria. These proteins are composed of a signal peptide, a {beta}-barrel that serves as an anchor in the outer membrane, and an extracellular passenger domain responsible for adhesion. Autotransporters rely on BamA for their insertion in the outer membrane (OM), but specific helper proteins, such as TpgA and SadB have been described to promote the surface exposure of trimeric autotransporters (TAAs), a specialized subclass of autotransporters forming homotrimer adhesins. To identify domains or proteins that could help TAAs secretion, we analyzed a recent dataset of all trimeric autotransporters found across the bacterial tree of life. While we did not find additional potential helper proteins for OM translocation, we found that the extended signal peptide (ESPR), sometimes found in TAAs, is associated with longer adhesins both for TAAs and type Va autotransporter adhesins. ESPRs are found in all bacteria but Fusobacteriia and Alphaproteobacteria. We also identified in Burkholderia, Veillonellales and Pasteurellales a DUF2827 domain proteins as potential glycosyltransferases constantly associated with TAAs. Finally, e describe the existence of extra periplasmic domains in some TAAs, featuring either a coiled-coil domain or a peptidoglycan-binding domain. Our research show that there is a strong phylogenetic separation between Terrabacteria, almost invariably displaying additional periplasmic domains, and Gracilicutes (represented by Proteobacteria) where they are largely absent. This suggests that the presence these domains might be correlated with specific Terrabacteria OM features. Using the diderm Firmicute Veillonella parvula as a model, we demonstrate that the absence of periplasmic domains in TAAs leads to a significant protein degradation, yet they are not essential for adhesin trimerization or secretion. Additionnaly, we show that the SLH domains of V. parvula TAAs excludes them from the septum during division, but that this exclusion is not crucial for adhesin function or stability in the tested conditions. Altogether, these results illuminate the genetic flexibility and modularity of autotransporters, enhancing our understanding of this important class of adhesins in diderm bacteria.

microbiology↗

bioRxiv2025

A Chryseobacterium massiliae pore-forming MACPF domain protein mediates intra and interspecies competition against Bacteroides

Microbiota play crucial roles in host health, including protection against pathogens through competitive interactions between commensal and pathogenic bacteria that are mediated by direct contact or secreted factors. We previously demonstrated that Chryseobacterium massiliae, a zebrafish commensal, protects larvae against infection by Flavobacterium covae (formerly F. columnare). Here, we investigated whether interference interactions contribute to this protective effect. We found that C. massiliae culture supernatant inhibits F. covae growth and a transposon mutagenesis screen identified mutants lacking this activity. All identified mutants carried insertions in a gene encoding a protein homologous to Bacteroidales BSAP pore-forming toxins, characterized by a Membrane Attack Complex/Perforin (MACPF) domain. We showed that this protein, which we named CSAP-1 (for Chryseobacterium Secreted Antimicrobial Protein) displays bactericidal, pore-forming activity that lyses F. covae cells. Unlike BSAP proteins from Bacteroides spp., CSAP-1 displays broader antagonistic activity, targeting multiple species across the Flavobacterium and Chryseobacterium genera - thus mediating interspecies and intergenus inhibition within Bacteroidetes. Although CSAP-1 is not essential for the in vivo protective effect of C. massiliae, administration of purified CSAP-1 alone confers significant protection to zebrafish larvae against sensitive F. covae infection. This study therefore identifies CSAP-1 as the first MACPF protein from C. massiliae with broad-spectrum inhibitory activity against members of the order Flavobacteriales. These findings highlight CSAP-1 as a promising candidate for the development of novel antimicrobial strategies and warrant further mechanistic investigation.

microbiology↗

bioRxiv2020

Gnotobiotic rainbow trout (Oncorhynchus mykiss) model reveals endogenous bacteria that protect against Flavobacterium columnare infection

The health and environmental risks associated with antibiotic use in aquaculture have promoted bacterial probiotics as an alternative approach to control fish infections in vulnerable larval and juvenile stages. However, evidence-based identification of probiotics is often hindered by the complexity of bacteria-host interactions and host variability in microbiologically uncontrolled conditions. While these difficulties can be partially resolved using gnotobiotic models harboring no or reduced microbiota, most host-microbe interaction studies are carried out in animal models with little relevance for fish farming. Here we studied host-microbiota-pathogen interactions in a germ-free and gnotobiotic model of rainbow trout (Oncorhynchus mykiss), one of the most widely cultured salmonids. We demonstrated that germ-free larvae raised in sterile conditions displayed no significant difference in growth after 35 days compared to conventionally-raised larvae, but were extremely sensitive to infection by Flavobacterium columnare, a common freshwater fish pathogen causing major economic losses worldwide. Furthermore, re-conventionalization with 11 culturable species from the conventional trout microbiota conferred resistance to F. columnare infection. Using mono-re-conventionalized germ-free trout, we identified that this protection is determined by a commensal Flavobacterium strain displaying antibacterial activity against F. columnare. Finally, we demonstrated that use of gnotobiotic trout is a suitable approach for the systematic identification of both endogenous and exogenous probiotic bacterial strains that may protect teleostean hosts against F. columnare and other pathogens. This study establishes a novel and ecologically-relevant gnotobiotic model that will improve the sustainability and health of aquaculture.

microbiology↗

bioRxiv2020

Mining zebrafish microbiota reveals key community-level resistance against fish pathogen infection

The long-known resistance to pathogens provided by host-associated microbiota fostered the notion that adding protective bacteria could prevent or attenuate infection. However, the identification of endogenous or exogenous bacteria conferring such protection is often hindered by the complexity of host microbial communities. Here, we used zebrafish and the fish pathogen Flavobacterium columnare as a model system to study the determinants of microbiota-associated colonization resistance. We compared infection susceptibility in germ-free, conventional and re-conventionalized larvae and showed that a consortium of 10 culturable bacterial species are sufficient to protect zebrafish. Whereas survival to F. columnare infection does not rely on host innate immunity, we used antibiotic dysbiosis to alter zebrafish microbiota composition, leading to the identification of two different protection strategies. We first identified that the bacterium Chryseobacterium massiliae individually protects both larvae and adult zebrafish. We also showed that an assembly of 9 endogenous zebrafish species that do not otherwise protect individually confer a community-level resistance to infection. Our study therefore provides a rational approach to identify key endogenous protecting bacteria and promising candidates to engineer resilient microbial communities. It also shows how direct experimental analysis of colonization resistance in low-complexity in vivo models can reveal unsuspected ecological strategies at play in microbiota-based protection against pathogens.

microbiology↗