For instance, -lactamase can be packaged into MVs released from Gram-positive bacteria, and co-incubation of such MVs with -lactam-sensitive species improves resistance to these antibiotics108,110. the amount of Lpp crosslinked to PG in the hyper-vesiculating mutant was 40% lower than that in wild-type prevents the formation of proper crosslinks between PG and Lpp and eventually leads to increased OMV production. Recent studies have also shown that this generation of OMVs in was affected by PG architecture, as OMVs from this bacterium were found to contain lower levels of the Sulfamonomethoxine three lytic transglycosylases MltA, MltB and Slt45. Together, these observations support a model in which OMVs bud off at sites with locally decreased levels of crosslinks between the outer membrane and PG and with locally reduced PG hydrolase activity (Physique 3A). Open in a separate window Physique 3 Proposed models for the biogenesis of outer membrane vesicles (OMVs). (A) The linkage between the outer membrane and the underneath peptidoglycan layer is usually disrupted. (B) A physical pressure induced by accumulation of misfiled or overexpressed envelope proteins pushes out outer membrane vesicles. (C) The accumulation of LPS molecules with atypical structures or charges prospects to the curvature of outer membrane. (D) Local curvature of bacterial outer membrane is stimulated by extracellular signals (OMV lipids differ from the lipids of the OM of the bacterium50. These findings have led to a model in which membrane curvature is usually induced by the accumulation of LPS molecules with atypical structures or charges (Physique 3C). LPS is the major constituent of the outer leaflet of the OM of most Gram-negative bacteria. The LPS molecules themselves are not homogeneous, as the length and content of the polysaccharide chain varies among the different molecules. It has been proposed that subsets of these molecules may gather in patches along the OM, inducing higher degrees of membrane curvature at particular locations, either due to charge repulsion51 or their molecular shape52. In addition, the Pseudomonas quinolone transmission (PQS) of can enhance anionic repulsions between lipopolysaccharide molecules, resulting in membrane blebbing by sequestering divalent cations, which are important in forming stabilizing salt bridges between the negatively charged B-band lipopolysaccharide molecules53,54,55. Recently, it was proposed that this PQS induces OMV formation through a mechanism of asymmetric growth of Sulfamonomethoxine the outer leaflet of the OM53,54,55 (Physique 3D). Even though PQS-based model is one of the best studied so far, whether it is utilized by other strains of Gram-negative bacteria to produce OMVs remains unclear. Phospholipid accumulation in the outer leaflet of the OM causes OMV biogenesis Recently, Roier and without compromising OM integrity. Similarly, mutations in homologues of also increased vesiculation. Using lipidome analyses, they further found that OMVs from VacJ/Yrb-defective mutants in were enriched in phospholipids and certain fatty acids. Given that PL transporters are essential for maintaining the lipid asymmetry in the OM, the asymmetric growth of phospholipids in the outer leaflet would initiate an outward bulging of the OM, leading to the generation of OMVs. These findings suggest a new general mechanism of OMV biogenesis based on phospholipid accumulation in the outer leaflet of the outer membrane. Importantly, this mechanism is Sulfamonomethoxine usually highly Sulfamonomethoxine conserved among Gram-negative bacteria and can account for OMV formation under all growth conditions56. Thus, this model of OMV biogenesis may be relevant to a broad range of Gram-negative bacteria and might Rabbit polyclonal to HRSP12 have important pathophysiological functions serovar Typhimurium as a model organism and tested the effect of lipid A remodeling on OMV biogenesis. They observed that expression of the lipid A deacylase PagL resulted in increased vesiculation without inducing an envelope stress response. Mass spectrometry analysis further revealed profound differences in the patterns of lipid A expression in the OM and OMVs, with deacylated lipid A forms accumulating exclusively in OMVs. These findings suggest a novel mechanism for OMV biogenesis that involves outer membrane remodeling through lipid A modification. The second model of OMV biogenesis was proposed by Turnbull produces shattered membrane fragments that rapidly form MVs. They recognized that a prophage. Sulfamonomethoxine