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Carbon Budding in the Ocean
Bacterial vesicles are gaining increasing attention for their roles in pathogenesis, but the abundance of these structures and their ecological roles in nonpathogenic contexts have received little notice. Biller et al. (p. 183; see the Perspective by Scanlan) provide evidence that membrane vesicles ∼100 nm in diameter are released by marine cyanobacteria and are a major feature of marine ecosystems. Studies of cultures of Prochlorococcus—the most abundant photoautotroph in the oligotrophic oceans—show that vesicles are continually released by this cyanobacterium and are abundant in the marine environment. These vesicles have properties that change the way we think about genetic and biogeochemical exchange among plankton and the dissolved organic carbon pool in marine ecosystems.
Many heterotrophic bacteria are known to release extracellular vesicles, facilitating interactions between cells and their environment from a distance. Vesicle production has not been described in photoautotrophs, however, and the prevalence and characteristics of vesicles in natural ecosystems is unknown. Here, we report that cultures of Prochlorococcus, a numerically dominant marine cyanobacterium, continuously release lipid vesicles containing proteins, DNA, and RNA. We also show that vesicles carrying DNA from diverse bacteria are abundant in coastal and open-ocean seawater samples. Prochlorococcus vesicles can support the growth of heterotrophic bacterial cultures, which implicates these structures in marine carbon flux. The ability of vesicles to deliver diverse compounds in discrete packages adds another layer of complexity to the flow of information, energy, and biomolecules in marine microbial communities.