The most abundant photosynthetic organism in the world sheds countless little sacs into the oceans, which could be having a dramatic impact on marine ecosystems, according to a new study. These microbial buds contain proteins and genetic material, which may influence the growth of other marine microbes and even protect them against viruses.
The oceans comprise the world’s largest ecosystem, and cyanobacteria — single-celled organisms that get their energy through photosynthesis — are the keystone group. One type of cyanobacteria, Prochlorococcus, is the most abundant photosynthetic organism on the planet, numbering in the billion billion billions. These tiny organisms account for about 10 percent of all photosynthesis on Earth, which forms the base of the food chain and provides the atmosphere with oxygen. Now, researchers at the Massachusetts Institute of Technology, led by biological oceanographer Sallie Chisholm, have found that cyanobacteria may play an even bigger role in the ecosystem than previously thought.
In a paper published online Thursday in Science, Chisholm’s team reported that cyanobacteria secrete vesicles — small, membrane-enclosed sacs — into the surrounding ocean. Chisholm first observed the vesicles in 2008 when one of her graduate students, Anne Thompson, spotted tiny buds on the surface of Prochlorococcus under an electron microscope. “Blebs, we called them,” Chisholm recalls, “like little bubbles.” A couple of years later, MIT postdoctoral fellow Steven Biller proposed that these blebs might be vesicles, based on their resemblance to vesicles from other species. He confirmed this by isolating the blebs under the electron microscope.
Analysis of the blebs’ contents revealed a variety of biological molecules: proteins, DNA, and RNA. Sequencing the DNA revealed that it came from a variety of microbes, not just Prochlorococcus. Thus, these vesicles seem to be a general feature of marine microorganisms.