A war without end - with earth’s carbon cycle held in the balance

Oregon State University: The greatest battle in Earth’s history has been going on for hundreds of millions of years - it isn’t over yet - and until now no one knew it existed, scientists reported today in the journal Nature.

In one corner is SAR11, a bacterium that’s the most abundant organism in the oceans, survives where most other cells would die and plays a major role in the planet’s carbon cycle. It had been theorized that SAR11 was so small and widespread that it must be invulnerable to attack.

In the other corner, and so strange-looking that scientists previously didn’t even recognize what they were, are “Pelagiphages,” viruses now known to infect SAR11 and routinely kill millions of these cells every second. And how this fight turns out is of more than casual interest, because SAR11 has a huge effect on the amount of carbon dioxide that enters the atmosphere, and the overall biology of the oceans.

“There’s a war going on in our oceans, a huge war, and we never even saw it,” said Stephen Giovannoni, a professor of microbiology at Oregon State University. “This is an important piece of the puzzle in how carbon is stored or released in the sea.”

Researchers from OSU, the University of Arizona and other institutions today outlined the discovery of this ongoing conflict, and its implications for the biology and function of ocean processes. The findings disprove the theory that SAR11 cells are immune to viral predation, researchers said.

“In general, every living cell is vulnerable to viral infection,” said Giovannoni, who first discovered SAR11 in 1990. “What has been so puzzling about SAR11 was its sheer abundance; there was simply so much of it that some scientists believed it must not get attacked by viruses.” What the new research shows, Giovannoni said, is that SAR11 is competitive, good at scavenging organic carbon, and effective at changing to avoid infection. Because of that, it thrives and persists in abundance even though it’s constantly being killed by the new viruses that have been discovered....

A SAR-11 bacterium infected with the pelagiphage virus. Photo courtesy of the University of Oregon