Outer membrane vesicles - offensive weapons or good Samaritans?

Abstract

Outer membrane vesicles (OMVs) from Gram-negative bacteria were first considered as artifacts and were followed with disbelief and bad reputation. Later, their existence was accepted and they became characterized as bacterial bombs, virulence bullets, and even decoys. Today, we know that OMVs also can be involved in cell-cell signaling/communication and be mediators of immune regulation and cause disease protection. Furthermore, OMVs represent a distinct bacterial secretion pathway selecting and protecting their cargo, and they can even be good Samaritans providing nutrients to the gut microbiota maintaining commensal homeostasis beneficial to the host. The versatility in functions of these nanostructures is remarkable and includes both defense and offense. The broad spectrum of usability does not stop with that, as it now seems that OMVs can be used as vaccines and adjuvants or vehicles engineered for drug treatment of emerging and new diseases not only caused by bacteria but also by virus. They may even represent new ways of selective drug treatment.

Keywords: defense; offense; outer membrane vesicles; versatility in functions.

Fig. 1

OMVs observed at the outer cell membrane in P. gingivalis with transmission electron microscopy. A: Membrane-blebbing OMVs in strain ATCC 33277^T (type I fimA strain). B: OMVs through the blebbing and pinching-off of the outer membrane in strain TDC 60 (type II fimA strain). Bars=200 nm.

Fig. 2

Entry of OMVs isolated from P. gingivalis ATCC 33277 into immortalized gingival epithelial cells. The cells were incubated with OMVs (30 µg/ml) for 15 min, then further incubated for the indicated times. For fluorescence microscopy, the cells were processed for staining for OMVs (green) and actin (Alexa Fluor 568-conjugated phalloidin red).