Get to Know the Newest Players in Global Ecology

Jan 13, 2014

A scanning electron micrograph of the marine bacterium, Prochlorococcus, shows tiny extracellular vesicles.
Credit Steven Biller

They have a cell membrane, genetic material, nutrients, and enzymes. But they're not alive. What are they? Extracellular vesicles, of course.

What?!? You've never heard of extracellular vesicles?

Don't worry, you're not alone.

The discovery that bacteria can essentially pinch off a portion of themselves and send it floating off into the environment dates back almost fifty years, but how and why has remained largely unanswered. And it was only last week that scientists at M.I.T. announced they'd discovered extracellular vesicles produced by marine bacteria. Here's what you need to know.


While the ocean is home to an amazing diversity of life, it turns out that the majority of the plant-like activity in the ocean can be attributed to just two closely related, particularly small bacteria – Prochlorococcus and Synechococcus (known around the lab as Pro and Syn, for short). Extracellular vesicles were first spotted in photographs of Prochlorococcus, but examination of the genetic material inside vesicles found in ocean water suggest that many marine species make vesicles.


Extracellular vesicles are microscopic spheres made of cellular components - pseudo-cells, if you will. They are essentially bubbles of cell membrane, stuffed full of nutrients, enzymes, and genetic material, then pinched off and sent floating away.


Ah, there's the rub. There are several possible functions for extracellular vesicles. They could be decoys for marine viruses, a food source for other bacteria (which, in addition to eating Pro and Syn, also - ironically - help them grow faster, perhaps by mopping up toxic byproducts of photosynthesis), or a means of exchanging genetic material.


How do Pro and Syn (or other marine bacteria, for that matter) make extracellular vesicles? How do they decide when to produce them, how many to release, or what to put into them? All open questions that Dr. Steve Biller, lead author of the new study, says he hopes to pursue in the near future.


Understanding how these tiny bacteria do what they do is, quite literally, important for all life on earth. Ocean microbes produce half the oxygen in our atmosphere, in the process, sucking an estimated third of carbon dioxide emissions out of the atmosphere.