Missing link found in the biology of cloud formation

Scientists have known for two decades that sulphur compounds that are produced by bacterioplankton as they consume decaying algae in the ocean cycle through two paths.

In one, a sulphur compound dimethylsulphide, or DMS, goes into the atmosphere, where it leads to water droplet formation - the basis of clouds that cool the Earth. In the other, a sulphur compound goes into the ocean's food web, where it is eaten and returned to seawater.

What they haven't known is how sulphur is routed one way or the other or why.

They also have wondered what if - in a time of growing concern about global warming - it was possible to divert the sulphur compound that goes into the oceans into the atmosphere, helping to mitigate global warming?

A study by researchers at the University of Georgia just published in Nature brings the possibility of using the sulphur cycle to mitigate global warming closer with the identification of the steps in the biochemical pathway that controls how bacteria release the sulphur compound methanethiol, or MeSH, into the microbial food web in the oceans and the genes responsible for that process.

"With our increased understanding of the sulphur cycle in the ocean," said study co-author William (Barny) Whitman, "we are now better able to evaluate the impacts of climate change on the process and the potential for its manipulation, which has been proposed as a way to mitigate global warming.

"It's wonderful to have this much understanding of a major biogeochemical process," noted Whitman, distinguished research professor and head of the department of microbiology in the Franklin College of Arts and Sciences.

In addition to elucidating the steps in the pathway and identifying the responsible genes, the team of UGA microbiologists, marine scientists and chemists discovered that the pathway is found widely, not only among bacterioplankton in the ocean but also in non-marine environments.

"The big mystery about bacteria is what they are doing in nature," Whitman said. "The organisms metabolise compounds for their own needs. We need to understand what they are getting out of it to understand what it means for the ocean, and now it will be possible to look at the environmental importance of this process and how it's regulated." That will help to answer the "why" of the two sulphur fates.

Co-authors of the Nature paper were UGA graduate students Chris Reisch and Vanessa Varaljay, department of microbiology; graduate student Melissa Stoudemayer and Jon Amster, professor and head, department of chemistry; and distinguished research professor Mary Ann Moran, department of marine sciences-all in the Franklin College of Arts and Sciences.

The collaborators in this study built on a line of research begun at UGA over a decade ago. Moran's early research showed that an abundant group of bacteria known as marine roseobacters play a role in moving dimethylsulphonioproprionate (DMSP), the chemical made by marine algae and released into the water upon their death, into the atmosphere as the compound dimethylsulphide (DMS).

Missing link found in the biology of cloud formation over the oceans