Socio-evolutionary role of bacterial membrane vesicles in cooperation and competition within microbial communities.

Microbial communities are shaped by social interactions that influence survival, resource access, and evolutionary trajectories. Most studies of microbial social evolution have focused on freely diffusible molecules such as siderophores and quorum-sensing signals, whereas the physical form in which extracellular products are delivered has received less attention. Bacterial membrane vesicles package enzymes, lipids, nucleic acids, and small metabolites into membrane particles. Membrane packaging slows cargo dispersal, protects labile cargo, and can restrict uptake through receptor-dependent binding. Here, we review vesicle-mediated interactions from the perspective of social evolution, with a primary focus on outer membrane vesicles released by gram-negative bacteria and drawing on gram-positive examples where informative. We first examine how the route of vesicle biogenesis influences cargo composition and cost to the producing cell, and consider how these differences may influence ecological function. We then discuss how limited dispersal and recipient bias may reduce benefit leakage and thereby help stabilize cooperation. Finally, we consider the conditions under which vesicles support antagonistic outcomes, including toxin delivery, lytic activity, and resource piracy. We argue that whether vesicles favour cooperation, privatization, or competition is not a fixed property but depends on the interplay among biogenesis route, the surface receptor repertoire of recipient cells, local relatedness, and environmental conditions including resource availability and niche overlap. We further highlight that bulk vesicle preparations confound analysis of functionally distinct vesicle subpopulations, underscoring the need to resolve vesicle type, biogenesis route, and recipient identity in spatially structured communities.