Gram‑negative bacteria release outer membrane vesicles (OMVs) as part of their normal growth. OMVs range up to 400 nm in size and contain nucleic acids, enzymes and proteins from their parent bacterium. The protein content of OMVs is thought to be reflective of their parent bacterium. However, few studies have compared the proteome of OMVs to that of their parent bacterium and examined how this changes throughout bacterial growth. In this study, we aimed to elucidate the contribution of bacterial growth stage on the proteome of Helicobacter pylori and their OMVs.
We identified that bacterial growth stage affected the size and protein composition of H. pylori OMVs. We found that OMVs isolated from different growth stages were significantly different in protein composition. In addition, we showed that the proteome of OMVs was vastly different to that of their parent bacterium throughout bacterial growth, suggesting that there is preferential packaging of bacterial proteins into OMVs. Furthermore, we determined that the predominant proteins contained within OMVs changed as bacterial growth progressed, indicating that the proteome of OMVs alters throughout bacterial growth. Gene ontology and functional enrichment analyses showed that proteins found in early log and stationary phase OMVs contribute to metabolic pathways, while proteins in late log phase OMVs contribute to cell signalling. Importantly, we identified that bacterial growth stage affected the inflammatory response mediated by OMVs in host cells.
Our findings highlight the previously unknown role of bacterial growth stage on regulating the protein cargo composition and immunostimulatory abilities of OMVs. These results show that the proteome and functions of OMVs isolated at different growth stages are not comparable to one another. Therefore, these findings emphasise the importance of considering bacterial growth stage at which OMVs are isolated from, as this has significant affects on their protein content and biological functions.