Reduced Sulfur Might Be Key To Ocean Function

"What does life in the ocean need to thrive?" Is a question biologists and oceanographers have asked for decades. It is also one climate scientists and even carbon sequestration companies are asking with increasing urgency. We do know that phytoplankton form the base of the marine food chain, and new research out of OSU provides an unexpected twist. We knew that nitrogen, phosphorus, and iron, were critical to phytoplankton production, now it appears 'reduced' sulfur is a key nutrient for one of the most abundant and smallest free-living single cell organisms in the ocean, SAR11.

The new insights into SAR11 have very large implications, possibly impacting how we understand the earths carbon cycle, marine ecosystems, and even cloud formation and climate change.Oregon State University researchers discovered SAR11 in 1990, and although it is one of the smallest organisms in the ocean, it plays a major role in the cycling of carbon on Earth. SAR11 also has one of the smallest genomes, and this may in fact be the reason it needs reduced sulfur to thrive.

"This appears to be part of the genomic streamlining that has made SAR 11 such an evolutionary success," said Steve Giovannoni, a professor of microbiology at OSU. "It's a very simple, lean machine, and by using sulfur produced by other sources it doesn't have to expend the energy to reduce this nutrient itself. It may have traded independent function for simplicity and energy efficiency."

"This is just really, really unusual," Giovannoni said. "It also raises the question of what other bacteria and phytoplankton have unsuspected nutrient requirements that we know nothing about."

These findings really can't be understated. SAR11 is a major reason why we can live on earth at all. By recycling organic carbon SAR11 provides the nutrients needed for the algae that in turn produce half of the oxygen we breath every day.

Interestingly, SAR11 might also be more directly responsible for contributing to cloud formation. One of the major sources of sulfur for phytoplankton is Dimethylsulfoniopropionate (DMSP), and is known to cause the unique 'ocean air' smell. DMSP is also plays an important role in climate models, as it is known to help in the formation of clouds that cause rain. Changes in the availability of nutrients could cause a change in how much DMSP is available, altering cloud formation and rain, creating climate change.

"There's a lot we still need to learn about the basic functions of marine ecology, because they can affect so many other things," Giovannoni said. "We certainly did not expect sulfur to be so important in this situation. When we look more, there will probably be more surprises."

Excellent photo attribution of phytoplankton bloom goes to the U.S. Geological Survey.
::OSU News