Micro-plants that form the base of the aquatic food chain; the nourishing organisms also use sunlight and carbon dioxide to generate organic carbon. For the first time these cyanobacteria were observed releasing "spherical packages" (vesicles) that provide carbon and nutrients to other organisms.
These vesicles also contain sneaky DNA which could allow for "gene transfer within and among communities of similar bacteria" and could even act as "decoys" that work to trick viruses, a Massachusetts Institute of Technology news release reported.
Researchers found the cyanobacteria Prochlorococcus and Synechoccocus were associated with large numbers of these vesicles; the "packages" were found in lab cultures containing cyanobacteria, nutrient-rich seawater taken off the New England coast, and nutrient-deficient water from the Sargasso Sea.
"The finding that vesicles are so abundant in the oceans really expands the context in which we need to understand these structures," postdoc Steven Biller, first author on the Science paper, said in the news release. "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."
Seawater samples were found to contain vesicles that displayed DNA from a "diverse array" of bacteria; this finding suggests vesicle production is common in a number of microbes. The researchers believed Prochlorococcus bacteria can produce these "nutrient packages" at a rate of a "billion billion billion per day" globally.
"Prochlorococcus is the smallest genome that can make organic carbon from sunlight and carbon dioxide and it's packaging this carbon and releasing it into the seawater around it," Professor Sallie Chisholm, the Lee and Geraldine Martin Professor of Environmental Studies in MIT's Department of Civil and Environmental Engineering and Department of Biology and lead investigator of the study, said. "There must be an evolutionary advantage to doing this. Our challenge is to figure out what it is."
The vesicles could help the cyanobacteria release substances that could act as toxins in their own body; since these same substances are nourishing to other creatures it can create a mutually beneficial relationship. The DNA contained in the vesicles could also aid in "horizontal gene transfer."
Another benefit of the vesicles is that they can work to fight viruses by acting as decoys. Phages ("viruses that attack bacteria") often attach themselves to vesicles.
"When a phage injects its DNA into the vesicle (making it impossible for the phage to reproduce in a living cell), it renders the phage inactive, according to Biller, who says the vesicles could be acting like chaff released by a fighter jet to divert missile attacks. A phage attached to a vesicle is effectively taken out of the battle, providing a creative means of deterrence," the news release reported.
The oceanic vesicle phenomenon was first noticed by then graduate student Anne Thompson back in 2008 when she noticed tiny "blebs" on the surface of Prochlorococcus cells.
"Marine cyanobacteria of the genera Prochlorococcus and Synechoccocus are the two most abundant phototrophs," biologist David Scanlan, a professor at the University of Warwick who was not involved in this research, said. "By releasing extracellular vesicles these organisms shed new light on the importance of such particles in the largest ecosystem on Earth -- the open ocean -- with implications for marine carbon cycling, mechanisms of horizontal gene transfer, and as a defense against phage attack.
