[Alteromonas macleodii vesicle diameter obtained with Cryo-EM micrographs] - Alteromonas macleodii vesicle diameter measured during Cryo-EM micrograph experiment (Collaborative Research: Extracellular vesicles as vehicles for microbial interactions in marine Black Queen communities)

Here we showed that Alteromonas facilitated greater exploitation of medium resources by Prochlorococcus, allowing them to grow to greater cell densities, delay entry into stationary phase, and avoid cell death in batch co-cultures, potentially by degrading autotoxic substances produced in dense Prochlorococcus cultures.

We further showed that heat-labile high-molecular weight exudates from Alteromonas were responsible for this effect. Alteromonas exudates contained a wide variety of proteins and demonstrated enzymatic activities, and both the composition and activity of the exudates changed after 500 generations of adaptation to a changed environment, suggesting some form of genetic regulation. Some of these proteins and activities may have been packaged within extracellular membrane vesicles, which we identified within Alteromonas exudates and found capable of physically associating with Prochlorococcus cells.