Gram‑negative bacteria release outer membrane vesicles (OMVs) that contribute to a number of bacterial functions including acting as antimicrobials that can lyse competing bacteria due to their bactericidal cargo. Bacteria produce OMVs via two main mechanisms, which involve budding from the cell surface during normal bacterial growth or via prophage induced explosive cell lysis. However, it is not known whether these different mechanisms of OMV biogenesis can influence their composition and biological functions. In this study, we examined whether the mechanisms of OMV biogenesis can regulate their cargo composition and subsequent antimicrobial functions.
We isolated OMVs from three Pseudomonas aeruginosa strains; PAO1 which produces OMVs naturally by budding and explosive cell lysis, PAO1Δlys which produces OMVs by budding alone, and PAO1Δlys pJN105lys which produces OMVs predominately by explosive cell lysis due to over-expression of lys. The antimicrobial activity of these OMVs was tested against Staphylococcus aureus and P. aeruginosa in order to determine if there were any differences in their functions based on their mechanism of biogenesis. We determined that the mechanism of biogenesis did not affect the antimicrobial activity of OMVs against S. aureus, as OMVs from all three strains could significantly inhibit the growth of S. aureus. However, only OMVs produced by explosive cell lysis were able to inhibit the growth of P. aeruginosa, suggesting that the mechanism of OMV biogenesis may regulate their antimicrobial functions. We are currently determining the protein content of OMVs from all three strains using proteomics to identify any biogenesis‑dependent selective packaging of proteins, in addition to further investigating the nature of this antimicrobial product and its association with OMVs.
Collectively, these results indicate that there are differences in the antimicrobial functions of OMVs against Gram‑negative and Gram‑positive bacteria that may be controlled via their mechanism of biogenesis. Additionally, our data provides insight into how OMV biogenesis can dictate the regulation of OMV cargo composition and their subsequent functions.