Biology subjects

Foulon, M.

Publications and source records attributed to Foulon, M..

5 recordsLinked to original sources

bioRxiv2026

Discoidins are cytosolic lectins that shape intracellular host defence by sensing virulence-associated mycobacterial glycolipids and glycopeptidolipids

Mycobacteria are surrounded by a dynamic, glycolipid-rich envelope that controls both virulence and immune recognition, yet how cytosolic lectins detect and interpret the organization of surface glycans during intracellular infection remains unclear. Here, we show that Dictyostelium discoideum discoidins act as cytosolic sensors of mycobacterial envelope organization. During Mycobacterium marinum infection, Discoidin A and Discoidin E assemble into foci on intracellular bacilli and bind surface-associated glycan patches. Using transposon mutagenesis, synthetic mycobacterial glycan arrays, biochemical fractionation and targeted envelope mutants, we find that discoidins recognize a restricted set of lipid-linked glycans enriched in methylated L-rhamnose motifs, including structures associated with LOS, PGL and GPL. Binding depends on the H-type lectin {beta}-galactoside-binding pocket and is inhibited by point mutations and TDG, a soluble disaccharide competitor, demonstrating glycan-dependent recognition. Specific assays led to exclusion of major structural carbohydrates, including AG-PG, AM/LAM, -glucan and TDM, while protease treatment of capsular material and fractionation of polar lipids, identified both GPL and LOS-like glycolipids as dominant discoidin ligands. Disruption of LOS biosynthesis or PDIM/PGL-dependent envelope organization reduced discoidin binding to intact bacteria even though some ligands remained detectable by dot blot in various envelope extracts. Thus, discoidins do not simply detect ligand abundance, but binding depends on envelope perturbations and unmasking of glycolipids and glycopeptidolipids. These findings reveal pathogen envelope glycans as direct targets of cytosolic lectin surveillance and establish discoidins as probes of mycobacterial envelope remodelling during intracellular infection. Author SummaryMany disease-causing bacteria are surrounded by a protective outer layer that helps them survive inside host cells and avoid being eliminated. This surface is not static, it can be remodelled during infection, changing which molecules are exposed to the host. How host cells detect these changes is still not fully understood. We studied this question using Dictyostelium discoideum, a single-celled amoeba that shares many cellular defence mechanisms with human immune phagocytes. We focused on discoidins, a family of proteins that bind sugars. We found that discoidins accumulate on intracellular Mycobacterium marinum, a close relative of Mycobacterium tuberculosis, the bacterium that causes tuberculosis, and recognize specific sugar-containing molecules exposed at the bacterial surface. Importantly, discoidins do not simply detect whether these molecules are present. Instead, they respond to how they are displayed and exposed on the bacterial surface. Changes in the organization of the bacterial outer layer strongly affected discoidin binding, masking or revealing specific target molecules. Our findings show that discoidins act as sensors of bacterial surface remodelling during infection. More broadly, they reveal an ancient mechanism by which host cells can monitor pathogens by detecting changes in the sugars exposed on their surface.

microbiology↗

bioRxiv2026

PDIM drives the transition from repairable to catastrophic EsxA-mediated vacuole membrane damage during Mycobacterium marinum infection

During infection, pathogenic mycobacteria damage the membrane of the Mycobacterium-containing vacuole (MCV), triggering host repair responses that preserve an intracellular permissive niche before bacteria escape to the cytosol at later stages. How the MCV transitions from repairable injury to catastrophic rupture remains poorly understood. Here, we dissected the respective contributions of the ESX-1 effectors EsxA/EsxB and the cell-envelope lipid phthiocerol dimycocerosate (PDIM) during Mycobacterium marinum infection of the amoeba Dictyostelium discoideum. Combining host reporters for membrane damage and repair with single and double bacterial mutants, we show that EsxA/EsxB and PDIM are both required for full intracellular virulence but act at distinct stages of MCV damage progression. Loss of EsxA/EsxB strongly reduced recruitment of ESCRT and autophagy reporters to the MCV, demonstrating that EsxA initiates repairable membrane lesions. In contrast, PDIM-deficient bacteria retained the ability to recruit early damage reporters and ESCRT machinery but showed reduced autophagy-associated repair, failed to efficiently acquire cytosolic perilipin coating, and remained largely confined within the MCV. Genetic disruption of host autophagy restored cytosolic access and intracellular growth of PDIM-deficient bacteria, indicating that PDIM is specifically required to overcome host repair capacity rather than to initiate damage. Importantly, the sequential requirement for EsxA and PDIM was conserved during infection of murine microglial BV-2 cells. Remarkably, PDIM-defective mutants induced lysenin recruitment, a reporter of sphingomyelin exposure, but progression to autophagy engagement was strongly decreased. Together, our results support a two-step model in which EsxA initiates MCV membrane damage, while PDIM amplifies these lesions towards catastrophic rupture, enabling escape to the cytosol and dissemination.

microbiology↗

bioRxiv2026

Intracellular compartmentalization shapes lipid access and metabolic fitness of mycobacteria

Intracellular mycobacteria encounter distinct metabolic environments as they transition between vacuolar and cytosolic compartments within host cells, yet how nutrient access is shaped by this compartmentalization remains poorly understood. Here, we use Mycobacterium marinum fatty acyl- CoA ligase 6 (FACL6) as a functional entry point to examine how lipid acquisition and processing are coordinated during intracellular infection. By combining host and bacterial genetic perturbations with dual RNA-sequencing and high-resolution imaging in genetically tractable amoebal infection models, and validating key phenotypes in mammalian cells, we show that lipid metabolic programs in intracellular mycobacteria are tightly linked to subcellular localization. Sterol utilization and neutral lipid storage are preferentially engaged during the intravacuolar phase, whereas cytosolic exposure is associated with reduced lipid accumulation. Deletion of facl6 disrupts this coordinated scenario, resulting in altered bacterial cell envelope architecture, premature membrane damage, defective neutral lipid storage, and reduced intracellular fitness despite enhanced cytosolic access. Together, these findings reveal that loss of FACL6 causes intrinsic defects in lipid handling and highlight how compartment-specific lipid environments shape the outcome of mycobacterial infection. TeaserLoss of FACL6 reveals how intracellular compartmentalization shapes mycobacterial lipid metabolism

cell biology↗

bioRxiv2025

Mycobacterial surface shedding drives bystander cells response during early intracellular infection

Mycobacteria possess a complex cell envelope whose outermost layer plays an underexplored role in host-pathogen interactions. Using Dictyostelium discoideum as a model host phagocyte, we show that Mycobacterium marinum rapidly sheds its envelope components, including surface proteins, carbohydrates, and virulence-associated lipids, within minutes of uptake. Shed material is actively trafficking within host endocytic pathways and disseminates to neighboring bystander cells, where it accumulates and triggers several responses. Notably, bystander cells exposed to shed material exhibit a transient delay in G1/S cell cycle progression, an activation of membrane damage-response pathways, and an enhanced resistance to subsequent mycobacterial infection. These phenotypes are recapitulated by infection-free conditioning with purified envelope extracts, demonstrating that superficial components of the envelope alone are sufficient to modulate host cell responses. Moreover, this priming effect is independent of bacterial viability or the Esx-1 secretion systems, underscoring the intrinsic immunomodulatory capacity of the envelope. Interestingly, bacteria that lose their outer layer are more frequently ubiquitinated, suggesting that host-driven stripping exposes molecules that are recognized by cytosolic sensors to mount a cell-autonomous defense. Together, our findings reveal that mycobacterial envelope shedding is a widespread, early event during intracellular infection that impacts both infected and bystander cells. These findings suggest that mycobacterial outermost envelope components can influence host cell physiology and contribute to early innate immune modulation, with implications for understanding the initial determinants of infection outcomes.

microbiology↗

bioRxiv2023

Overexpression of an apple broad range agglutinating lectin does not promote in planta resistance to fire blight and bacterial wilt.

Lectins, a large group of proteins present in all kingdoms of life can bind reversibly to glycans. The roles of plant lectins are diverse and include resistance to biotic or abiotic stress, notably bacterial resistance. A gene family encoding amaranthin-like lectins termed MdAGGs in apple (Malus domestica) has been identified to be overexpressed upon treatment with the plant resistance inducer acibenzolar-S-methyl (ASM) which promotes enhanced resistance to the fire blight disease caused by Erwinia amylovora (Ea). In this study, we first screened the ability of purified MdAGG10 to agglutinate bacterial cells in vitro among a range of bacterial species. Several bacterial species, either Gram positive or negative, either plant- or human-pathogens were found to be agglutinated by MdAGG10 in acidic conditions. Apple and Arabidopsis lines constitutively overexpressing MdAGG10 were generated and evaluated for their resistance to, respectively, Ea and Ralstonia solanacearum, both plant pathogens that were found in our screening. Despite MdAGG10 protein accumulated in tissues of both apple and Arabidopsis lines, they remained susceptible to their respective pathogens. Interestingly, in vitro agglutination of Ea by MdAGG10 did not impair bacterial growth, suggesting that other plant molecules are involved in the resistance to fire blight triggered after an ASM treatment.

plant biology↗