Gram negative bacteria produce nanoparticles known as outer membrane vesicles (OMVs) that contain bacterial products including DNA, proteins and lipids. Due to the ability of OMVs to package DNA within them, it is suggested that they are able to facilitate the transfer of genes between bacterial species. This study examines the ability of OMVs isolated from Gram negative Pseudomonas aeruginosa to package and transfer DNA to other bacteria.

In this study, OMVs were isolated from P. aeruginosa PAO9505 harbouring a plasmid encoding for antibiotic resistance. Examination of these OMVs using DNA staining revealed that DNA was associated on the outside, in addition to being contained within OMVs. In order to confirm that plasmid DNA was contained within OMVs, vesicles were treated with DNase and PCR was used to confirm the presence of intact plasmid DNA pre- and post-treatment. Plasmid-containing OMVs were used to transform recipient P. aeruginosa PAO9503, resulting in the generation of antibiotic resistant transformants. Moreover, as bacteria grown in conditions of stress increase their OMV production and alter their cargo composition, we investigated the ability of antibiotic stress to alter the amount of DNA contained within OMVs and their subsequent transformation efficiency. To do this, OMVs were isolated from P. aeruginosa exposed to a sublethal amount of gentamicin, and OMV production was quantified by NanoSight nanoparticle tracking analysis. We identified that antibiotic treatment of bacteria increased OMV production 3 fold, while decreasing their DNA content when compared to control OMVs. We are currently investigating the effect of sustained antibiotic treatment on altering the biogenesis of OMVs, their DNA composition and their ability to transfer DNA between bacteria.

Collectively these findings identify that OMVs are a mechanism used by bacteria to transfer DNA encoding for antibiotic resistance to other bacteria, and that stress affects the packaging of nucleic acids into OMVs. The outcomes of this study suggest that OMV-mediated DNA transfer may contribute to the spread of antibiotic resistance between bacterial strains.