Transcription Factor sigma(B) Plays an Important Role in the Production of Extracellular Membrane-Derived Vesicles in Listeria monocytogenes

Abstract

Gram-negative bacteria produce extracellular outer membrane vesicles (OMVs) that interact with host cells. Unlike Gram-negative bacteria, less is known about the production and role of extracellular membrane vesicles (MVs) in Gram-positive bacteria. The food-borne pathogen Listeria monocytogenes can survive under extreme environmental and energy stress conditions and the transcription factor sigma(B) is involved in this survival ability. Here, we first determined the production of MVs from L. monocytogenes and evaluated whether general stress transcription factor sigma(B) affected production of MVs in L. monocytogenes. L. monocytogenes secreted MVs during in vitro broth culture. The wild-type strain actively produced MVs approximately nine times more and also produced more intact shapes of MVs than those of the isogenic Delta sigB mutant. A proteomic analysis showed that 130 and 89 MV proteins were identified in the wild-type and Delta sigB mutant strains, respectively. Wild-type strain-derived MVs contained proteins regulated by sigma(B) such as transporters (OpuCA and OpuCC), stress response (Kat), metabolism (LacD), translation (InfC), and cell division protein (FtsZ). Gene Ontology (GO) enrichment analysis showed that wild-type-derived MV proteins corresponded to several GO terms, including response to stress (heat, acid, and bile resistance) and extracellular polysaccharide biosynthetic process, but not the Delta sigB mutant. Internalin B (InlB) was almost three times more contained in MVs derived from the wild-type strain than in MVs derived from the Delta sigB mutant. Taken together, these results suggest that sigma(B) plays a pivotal role in the production of MVs and protein profiles contained in MVs. L. monocytogenes MVs may contribute to host infection and survival ability under various stressful conditions.