Characterization of membrane vesicles in Alteromonas macleodii indicates potential roles in their copiotrophic lifestyle

Bacterial membrane vesicles (MVs) are likely abundant in the oceans. Based on observations from non-marine bacteria, MVs are involved in a range of physiological processes and play important roles in interactions between microbial cells. In this study we characterized MV production of six different strains of Alteromonas macleodii, a cosmopolitan marine bacterium. A. macleodii strains produced MVs at rates of up to 30 MVs cell-1 generation-1. The produced MVs had high morphological diversity that could potentially define their functional roles. Proteomic characterization revealed that MVs are rich in membrane proteins related to iron and phosphate uptake, as well as proteins with potential functions in biofilm formation. Furthermore, MVs were harboring hydrolytic enzymes. Taken together, our results suggest that in the largely oligotrophic oceans, A. macleodii MVs may support its growth through generation of extracellular "hotspots" that facilitate access to essential substrates. This study provides an important basis for further investigation of the ecological relevance of MVs in heterotrophic marine bacteria.