Scientists discover extracellular vesicles produced by ocean microbes

January 9, 2014

By Denise Brehm
Civil & Environmental Engineering

Marine cyanobacteria — tiny ocean plants that produce oxygen and make organic carbon using sunlight and CO2 — are primary engines of Earth’s biogeochemical and nutrient cycles. They nourish other organisms through the provision of oxygen and with their own body mass, which forms the base of the ocean food chain.

Scientists in Sallie (Penny) Chisholm's lab documented the first extracellular vesicles produced by ocean microbes. The arrow points to one of these spherical vesicles in this scanning electron micrograph of the cyanobacteria, Prochlorococcus. Image / Steven Biller, Chisholm Lab
Scientists in Sallie (Penny) Chisholm's lab documented the first extracellular vesicles produced by ocean microbes. The arrow points to one of these spherical vesicles in this scanning electron micrograph of the cyanobacteria, Prochlorococcus. Image / Steven Biller, Chisholm Lab

Now scientists at MIT have discovered another dimension of the outsized role played by these tiny cells: The cyanobacteria continually produce and release vesicles, spherical packages containing carbon and other nutrients that can serve as food parcels for marine organisms. The vesicles also contain DNA, likely providing a means of gene transfer within and among communities of similar bacteria, and they may even act as decoys for deflecting viruses.

In a paper published this week in Science, postdoc Steven Biller, Professor Sallie (Penny) Chisholm, and co-authors report the discovery of large numbers of extracellular vesicles associated with the two most abundant types of cyanobacteria, Prochlorococcus and Synechoccocus. The scientists found the vesicles (each about 100 nanometers in diameter) suspended in cultures of the cyanobacteria as well as in seawater samples taken from both the nutrient-rich coastal waters of New England and the nutrient-sparse waters of the Sargasso Sea. 

Although extracellular vesicles were discovered in 1967 and have been studied in human-related bacteria, this is the first evidence of their existence in the ocean.

“The finding that vesicles are so abundant in the oceans really expands the context in which we need to understand these structures,” says Biller, first author on the Science paper. “Vesicles are a pr