Pelagibacterales (SAR11)
Description and Significance
Pelagibacterales is an order in the Alphaproteobacteria composed of free-living heterotrophic bacteria. (4) They are most abundant group of marine microorganisms worldwide, making them key players in the global carbon cycle. The order was originally named following its discovery in the Sargasso Sea by Stephen Giovannoni, a professor of microbiology at Oregon State University.()(5) SAR11 has several unique characteristics, including the smallest known genetic structure of any independent cell. Through sheer numbers, this microbe has a huge role in consuming organic carbon, which it uses to generate energy while producing carbon dioxide and water in the process. SAR11 recycles organic matter, providing the nutrients needed by algae to produce about half of the oxygen that enters Earth's atmosphere every day.This carbon cycle ultimately affects all plant and animal life on Earth. (5)
"Because of their huge numbers, these cells are an important part of models that aim to understand and predict long-term patterns of carbon sequestration in the oceans," Giovannoni said.
"Microbes fix half of the oxygen in the air we breathe and drive every biogeochemical cycle that fuels Earth," Sullivan added. "Most of this happens in the oceans, and it turns out the most abundant microbes on the planet are the SAR11 bacteria."
Other contributors to this research included scientists at the University of California, San Diego’s National Center for Microscopy and Imaging Research and the Monterey Bay Aquarium Research Institute, which provided opportunity to sample viruses from nature.
Funding for the methods development and genomic sequencing was provided by the Gordon and Betty Moore Foundation Marine Microbiology Initiative and the Department of Energy Joint Genome Institute.
the SAR11 clade have the smallest genomes of any free-living microorganism. (2)(3) SAR11 make up about a third of the marine microorganisms in the oceans’ surface layers and its population rises and falls with seasonal shifts from summer to winter. (3)
