DNA-bearing membrane vesicles produced by Ahrensia kielensis and Pseudoalteromonas marina

Outer membrane vesicles (OMVs) derived from the alphaproteobacterium Ahrensia kielensis and from Pseudoalteromonas marina, a gammaproteobacterium, were sampled from liquid cultures in order to extract the MV-associated DNA, establish a shotgun library, and sequence randomly chosen clones to determine the origins of their DNA. We show that OMVs from A. kielensis and from P. marina both harbour DNA larger than 20 or 30 kbp. Transmission electron microscopical inspection of OMVs of A. kielensis and P. marina showed two types of vesicles: bilayered OMVs with a diameter between 30 and 250 nm and double bilayered OMVs ranging between 80 and 200 nm. Bilayered OMVs are either characterized by the presence of a large electron-dense substance or are elctron translucent. Double bilayered OMVs contained an electron dense substance in the core region surrounded by the second bilayer. 30,094 bp of the genome from OMV of A. kielensis and 45,981 bp of that from P. marina were sequenced. The results indicated that all sequences were single copy and that all sequences, with one exception, were similar to prokaryotic sequences, inserted viral sequences were not detected.