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Oceans of Microbes
Most of our oxygen comes from the oceans, where microbes account for more than half of the organic mass. Without microbes, the nutrients in the ocean would not be recycled. Dr. Steven Giovannoni, a marine microbiologist at Oregon State University, has found microbes in the most unusual places in the ocean.

Giovannoni wanted to know if microbes could live in the most nutrient poor regions of the ocean. The clear water of the Sargasso Sea in the southwestern region of the Atlantic Ocean is relatively poor in nutrients. By comparison, coastal waters are rich in organic nutrients, fed by the coast and the shallow waters.

Giovannoni wondered if microbes had adapted to this environment too. He theorized that nothing had been found there before because the microbial life was probably much smaller in a nutrient poor environment. A smaller microbe would require less nutrients.

After collecting water samples onboard a research vessel, Giovannoni and his team started their search for microbial life. Giovannoni chemically broke open all of the different microbes potentially in the water. The messy results were billions of different DNA fragments, all mixed together.

Next they compared individual strands of the DNA to a database of DNA sequences. One by one, they were able to identify known microbes for each strand. But eventually they found a strand that didn't belong to any known microbe. They called that strand SAR 11, meaning the 11th gene from the Sargasso samples.

Their next goal was to grow SAR 11 in the lab, a very difficult task for most microbes. The trick was to feed the microbe exactly what it wanted to eat. But this was a finicky microbe.

After months of experimentation, Stephanie Connon, one of Giovannoni's graduate students, found the right recipe for the microbe. She also managed to get a photograph of the tiny microbe. After cultivating more SAR 11, they were able to collect enough DNA to sequence its gene.

When they published their findings, other researchers started looking for SAR 11. Remarkably, they found SAR 11 in water everywhere they looked. Giovannoni realized that he was on the trail of possibly one of the most abundant life forms on the planet. It demonstrated how pervasive microbes are on this planet.

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