Extracellular vesicles (EVs) are vesicles secreted into the extracellular environment. These secreted vesicles contain specific miRNAs and proteins. Many bacteria are known to release EVs with essential functions such as mediating intercellular communications. However, the biogenesis and functions of EVs released by photoautotrophs remain largely unclear. Marine cyanobacterium Prochlorococcus is the smallest but most abundant photosynthetic organism in the marine ecosystem. It is proved to generate a large number of EVs continuously during cell growth. Such abundant marine EVs are considered to play important roles. Prochlorococcus EVs have been shown to promote the growth of heterotrophic bacteria. The cell division of Prochlorococcus can be synchronized under a light-dark cycle, but i...[ Read more ]

Extracellular vesicles (EVs) are vesicles secreted into the extracellular environment. These secreted vesicles contain specific miRNAs and proteins. Many bacteria are known to release EVs with essential functions such as mediating intercellular communications. However, the biogenesis and functions of EVs released by photoautotrophs remain largely unclear. Marine cyanobacterium Prochlorococcus is the smallest but most abundant photosynthetic organism in the marine ecosystem. It is proved to generate a large number of EVs continuously during cell growth. Such abundant marine EVs are considered to play important roles. Prochlorococcus EVs have been shown to promote the growth of heterotrophic bacteria. The cell division of Prochlorococcus can be synchronized under a light-dark cycle, but it is currently unknown whether the diel cycle affects the generation and features of EVs. To deepen our understanding of EVs in the marine ecosystem, it is important to purify and characterize EVs released from marine bacteria. Here, we developed a biochemical approach to isolate EVs released by Prochlorococcus MED4 culture based on a well-established approach to purify EVs released by mammalian cells. Transmission electron microscopy analysis suggested that the majority of MED4 EVs were not circular but elliptical. Nanoparticle tracking analysis indicated that the majority of MED4 EVs were 50~150nm in diameter. Label-free mass spectrometry combined with enrichment analysis revealed that the protein compositions in MED4 cells and in EVs were different, suggesting that EVs are enriched with specific proteins. We identified 160 proteins specifically enriched in EVs, and more than half of them were related to catalytic activity. In addition, the Prochlorococcus secret EVs faster in the dark phase than the light phase.