The ocean has always been one of the most mysterious parts of the planet, because its entire vastness and depth cannot be completely reached by human beings, even with the use of cutting-edge science or technology. It holds the world's largest ecosystem, and is home to organisms both extremely large and microscopic. One such microscopic organism has just been studied by Massachusetts Institute of Technology scientists, who were baffled by the microscopic bubbles they observed emanating from it.

It turned out that these microscopic bubbles were in fact microbial buds, or vesicles, given off by cyanobacteria, or blue green algae, aquatic and photosynthetic organisms that are also a source of food for marine organisms.

What the researchers found were vesicles specifically from Prochlorococcus and Synechoccocus, two of the most abundant types of cyanobacteria. These microorganisms that are less than a thousandth of a millimeter in diameter continually produce and release "inflated-beach-ball-like small spherical structures" into the ocean, said Steven Biller, the paper's lead author. These are the vesicles, rich with carbon and other nutrients, and with a lifespan of two weeks or more.

The study was published in the journal Science, and researchers said that what they discovered were large extracellular vesicles from waters of both New England and the Sargasso Sea. Although New England waters were nutrient-rich and Sargasso Sea waters were nutrient-sparse, the bacteria still released vital nutrients from their body.

Biological oceanographer Sallie Chisholm, who led the study, said that cyanobacteria may play an even bigger role in the ecosystem than previously thought. Because of their abundance and because of the biomolecules that are inside their body, the bacteria may be a significant source of organic carbon, nitrogen, and phosphorus on which other organisms might feed. Also, because the vesicles contain DNA, they may facilitate the exchange of genetic material between individual bacteria, a process known as horizontal gene transfer. Most significantly, the vesicles may help defend against viruses, because they can act as cellular decoys, so they don't infect the cyanobacteria.

"The finding that vesicles are so abundant in the oceans really expands the context in which we need to understand these structures," said Biller. "Vesicles are a previously unrecognized and unexplored component of the dissolved organic carbon in marine ecosystems, and they could prove to be an important vehicle for genetic and biogeochemical exchange in the oceans."

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