Salt stress affects global protein expression profiles of extracellular membrane-derived vesicles of Listeria monocytogenes

Our previous study has suggested that Listeria monocytogenes produces extracellular membrane vesicles (MVs) and its general stress transcription factor sigma B (σ^B) affects the production of MVs under energy stress. The objective of this study was to evaluate the production of MVs and perform global protein profiling for MVs with or without salt stress to understand the function of MVs in the pathogenesis of L. monocytogenes. When cells of L. monocytogenes were grown under 0.5 M salt stress, protein concentrations of MVs derived from wild-type strain and its isogenic ΔsigB mutant were approximately doubled compared to those of MVs derived from cells without salt stress. Proteomic analyses showed that the number of MV proteins expressed in wild-type strain was similar to that in ΔsigB mutant under salt stress. However, global protein expression profiles were dramatically changed under salt stress compared to those without salt stress. Fifteen σ^B dependent proteins were expressed in MVs of wild-type strain under salt stress, including osmolyte transporter OpuCABCD. In addition, MVs produced by salt stressed wild-type and ΔsigB mutant inhibited biofilm formation abilities of both strains. Taken together, our results suggest that salt stress can promote the production of MVs involved in carnitine transporter proteins, with σ^B playing a pivotal role in biological event.