Biology subjects

Brasseur, G.

Publications and source records attributed to Brasseur, G..

5 recordsLinked to original sources

bioRxiv2026

The Type VI secretion effector TpeX expands the pore-forming virulence arsenal of Pseudomonas aeruginosa

The type VI secretion system (T6SS) is a major weapon used by Pseudomonas aeruginosa to antagonize competing bacteria through the delivery of a diverse repertoire of toxic effectors. Although several P. aeruginosa T6SS effectors target bacterial membranes, the mechanisms underlying membrane disruption remain poorly characterized. Here, we study TpeX (PA5265), an accessory T6SS effector from P. aeruginosa PAO1 with structural similarity to the VasX pore-forming effector of Vibrio cholerae. We show that membrane-targeted TpeX exerts a bactericidal activity in Escherichia coli, resulting in dissipation of the membrane potential and loss of membrane integrity. The TpeX C-terminal region containing the predicted colicin-like transmembrane domain is sufficient to confer toxicity, although with reduced activity, supporting its role as the membrane-disrupting module. TpeX also oligomerizes upon membrane targeting, forming at least dimers, and structural modelling predicts a membrane-embedded pore compatible with the observed permeabilization phenotype. We further identify TpiX (PA5264), the protein encoded by the downstream gene, as the cognate immunity protein, which partially protects cells from TpeX toxicity and interacts with TpeX. Finally, AlphaFold 3 modelling predicts an interaction between TpeX and the HcpB-VgrG6 T6SS spike, suggesting a possible mechanism for effector recruitment and delivery. Together, our results identify TpeX as a bactericidal, colicin-like pore-forming T6SS effector whose membrane activity is controlled by a cognate immunity protein, thereby expanding the repertoire of membrane-targeting weapons used by P. aeruginosa in interbacterial competition.

microbiology↗

bioRxiv2025

Oxygen as a primary selective pressure for photo-endosymbiosis evolution

Photosymbiosis through eukaryotic or eukaryotic - prokaryotic associations provide mainly carbon and oxygen to the living world, however the mechanisms behind their evolution remain unknown. Here we develop a naive system based on the predatory ciliate Tetrahymena thermophila, not known for hosting symbiont, to recapitulate early events leading to photosymbiosis evolution. T. thermophila was found to readily phagocyte eukaryotic algae (Chlorella variabilis) or cyanobacteria (Synechoccocus elongatus) that can reach high numbers within predatory cells. Feeding with either prey in a low carbon environment provide little or no growth advantage to T. thermophila. In contrast, in anoxic environment, both intracellular C. variabilis or S. elongatus can readily support growth of T. thermophila in the light but not in the dark, demonstrating that oxygen supply in hospite can be an initial feature supporting further photo-endosymbiosis evolution. This suggests that it is unlikely that carbon metabolites produced by phototrophs could have represented a selective advantage for the evolution of photosymbionts. Although most extant photosymbiosis are based on carbon supply to the host cell, we therefore propose that it is a secondary event occurring from initial evolution in anoxic or hypoxic conditions, where O2 production was crucial for establishing the initial steps of photosymbiosis.

evolutionary biology↗

bioRxiv2021

A Tad-like apparatus is required for contact-dependent prey killing in predatory social bacteria

Myxococcus xanthus, a soil bacterium, predates collectively using motility to invade prey colonies. Prey lysis is mostly thought to rely on secreted factors, cocktails of antibiotics and enzymes, and direct contac with Myxococcus cells. In this study, we show that on surfaces the coupling of A-motility and contact-dependent killing is the central predatory mechanism driving effective prey colony invasion and consumption. At the molecular level, contact-dependent killing involves a newly discovered type IV filament-like machinery (Kil) that both promotes motility arrest and prey cell plasmolysis. In this process, Kil proteins assemble at the predator-prey contact site, suggesting that they allow tight contact with prey cells for their intoxication. Kil-like systems form a new class of Tad-like machineries in predatory bacteria, suggesting a conserved function in predator-prey interactions. This study further reveals a novel cell-cell interaction function for bacterial pili-like assemblages.

microbiology↗

bioRxiv2020

CglB adhesins secreted at bacterial focal adhesions mediate gliding motility

AO_SCPLOWBSTRACTC_SCPLOWThe predatory deltaproteobacterium Myxococcus xanthus uses a helically-trafficked motor at bacterial focal adhesion (bFA) sites to power gliding motility. Using TIRF and force microscopy, we herein identify the integrin I-domain-like outer-membrane (OM) lipoprotein CglB as an essential substratum-coupling protein of the gliding motility complex. Similar to most known OM lipoproteins, CglB is anchored on the periplasmic side of the OM and thus a mechanism must exist to secrete it to the cell surface in order for it to interact with the underlying substratum. We reveal this process to be mediated by a predicted OM {beta}-barrel structure of the gliding complex. This OM platform was found to regulate the conformational activation and secretion of CglB across the OM. These data suggest that the gliding complex promotes surface exposure of CglB at bFAs, thus explaining the manner by which forces exerted by inner-membrane motors are transduced across the cell envelope to the substratum; they also uncover a novel protein secretion mechanism, highlighting the ubiquitous connection between secretion and bacterial motility.

microbiology↗

bioRxiv2020

Modulation of bacterial multicellularity via spatiotemporal polysaccharide secretion

AO_SCPLOWBSTRACTC_SCPLOWThe development of multicellularity is a key evolutionary transition allowing for differentiation of physiological functions across a cell population that confers survival benefits; among unicellular bacteria, this can lead to complex developmental behaviours and the formation of higher-order community structures. Herein, we demonstrate that in the social {delta}-proteobacterium Myxococcus xanthus, the secretion of a novel secreted biosurfactant polysaccharide (BPS) is temporally and spatially modulated within communities, mediating swarm migration as well as the formation of multicellular swarm biofilms and fruiting bodies. BPS is a type IV pilus-inhibited acidic polymer built of randomly-acetylated {beta}-linked tetrasaccharide repeats. Both BPS and the "shared good" EPS are produced by dedicated Wzx/Wzy-dependent polysaccharide assembly pathways distinct from that responsible for spore coat assembly. To our knowledge, such pathways have never-before been explicitly shown to synthesize a biosurfactant. Together, these data reveal the central role of secreted polysaccharides in the intricate behaviours coordinating bacterial multicellularity.

microbiology↗