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Marine Cyanobacteria Releasing 'Snack Packs' : Study Finds

Jan 11, 2014 05:56 AM EST
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marine cyanobacterium Prochlorococcus
Scanning electron micrograph of the marine cyanobacterium Prochlorococcus, with small vesicles visible near the cell surface.

(Photo : Steven Biller, MIT)

Researchers have found that oceans are filled with many "food parcels," containing carbon and nitrogen. These lunch-packs are made by tiny cyanobacteria.

Marine cyanobacteria are at the very bottom of the food chain. These nitrogen-fixers provide nutrients to other organisms. In the latest study, researchers at NSF's Center for Microbial Oceanography found that these tiny cells release vesicles. This is the first time that the spherical organelles have been found in the ocean.

Lab experiments have shown that these vesicles are quite stable, surviving for two weeks or more. Researchers also found that these packages contain enough carbon to help non-photosynthetic bacteria grow.

The study is published in the journal Science.                          

Invisible Food Network of the Ocean

The study team found vesicles- about 100 nanometers in diameter- in sea water samples obtained from both nutrient-rich and nutrient-poor waters. The food packages were also found in cultures of cyanobacteria.

Apart from serving as a food source and a genetic transfer vehicle, these packages might also deflect viruses, researchers said. Previous research has shown that viruses are more likely to attack bacteria that have vesicles in them.

"The finding that vesicles are so abundant in the oceans really expands the context in which we need to understand these structures," said Massachusetts Institute of Technology (MIT) postdoc Steven Biller and first author of the study. "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."

Genetic analysis of the material in the vesicle showed a wide diversity, suggesting that several marine microbes were ejecting these organelles into the open sea, according to a news release.

Prochlorococcus is marine cyanobacteria found dominantly in oceans and is responsible for most of the photosynthesis occurring in the water. Biller and colleagues estimate that these bacteria alone spew billions upon billions of these food packages in the sea and increases carbon levels in nutrient-poor waters.

There is no free lunch

Researchers were amazed that the bacterium spends so much energy to produce food and just throws it out. The team later found that Prochlorococcus has lost its ability to neutralize certain toxins and that it depends on nonphotosynthetic bacteria to break down these chemicals, making the relationship beneficial to both organisms.

"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," said Sallie (Penny) Chisholm from MIT's Department of Civil and Environmental Engineering and Department of Biology, lead investigator of the study. "There must be an evolutionary advantage to doing this. Our challenge is to figure out what it is.

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