In every teaspoon of seawater there are at least 100,000 SAR11 - the prefix stands for "Sargasso" - cells. In the Atlantic Ocean near Bermuda, one third to one half of the cells present are SAR11. That's 200,000 to 300,000 cells per milliliter. In the coastal waters of the United States, the population may reach one million cells per milliliter. SAR11 cells are the single most successful group of bacteria in the oceans.

Bacteria are known for their ability to transform a myriad of substances; they are the agents that make the earth's geochemical cycles turn, converting carbon, nitrogen and other minerals from one form into another. But SAR11's exact role is still veiled in mystery. SAR11 research is heating up, and scientists hope that soon the biochemical mechanisms that allow this organism to dominate the seas will be revealed by genomics.

SAR11 was the first major group of uncultured bacteria to be discovered when genetic methods were introduced to study microbial diversity in nature. Uncultured bacteria are species that scientists have not been to coax to reproduce in a laboratory. The first SAR11 gene was cloned from DNA collected at BIOS's Hydrostation "S" in April 1986. The use of gene cloning technology for studying microbial diversity blossomed throughout the 1990s. During this period, microbiologists changed their point of view, recognizing that many of the bacteria that are important in the natural world could not be grown in scientific laboratories. To study these uncultured organisms, scientists had to resort to increasingly elaborate genetic methods.

In a collaboration between Oregon State University and Diversa Corporation, the SAR11 genome was completely sequenced. The genome of this relatively simple cell has enough DNA to code for one to two thousand genes. In comparison, the human genome has an estimated 30,000 to 40,000 genes. With the complete sequence in hand, biologists can now look for genes that reveal how SAR11 obtains carbon, nitrogen, phosphorous and energy - all necessary for life. Its genome sequence may help unlock the secret of SAR11's incredible success as a competitor in the global oceans.

Back to: Oceanic Microbial Observatory

Oceanic Microbial Observatory Home Page http://www.lifesci.ucsb.edu/~carlson/index.html