The composition and function of<i>Enterococcus faecalis</i>membrane vesicles

Abstract

Membrane vesicles (MVs) contribute to various biological processes in bacteria, including virulence factor delivery, antimicrobial resistance, host immune evasion and cross-species communication. MVs are frequently released from the surface of both Gram-negative and Gram-positive bacteria during growth. In some Gram-positive bacteria, genes affecting MV biogenesis have been identified, but the mechanism of MV formation is unknown. In <i>Enterococcus faecalis</i>, a causative agent of life-threatening bacteraemia and endocarditis, neither mechanisms of MV formation nor their role in virulence has been examined. Since MVs of many bacterial species are implicated in host-pathogen interactions, biofilm formation, horizontal gene transfer, and virulence factor secretion in other species, we sought to identify, describe and functionally characterize MVs from <i>E. faecalis</i>. Here, we show that <i>E. faecalis</i> releases MVs that possess unique lipid and protein profiles, distinct from the intact cell membrane and are enriched in lipoproteins. MVs of <i>E. faecalis</i> are specifically enriched in unsaturated lipids that might provide membrane flexibility to enable MV formation, providing the first insights into the mechanism of MV formation in this Gram-positive organism.