Deep-sea bacteria caught releasing carbon into atmosphere

These deep-sea bacteria dissolve rocks containing carbon, releasing carbon dioxide into the ocean (a vast carbon sink) and atmosphere. The discovery of this previously unknown carbon source will permit more accurate estimates for the volumes of carbon dioxide entering the atmosphere.

“If CO2 is being released into the ocean, it’s also being released into the atmosphere, because they’re constantly interchanging gases between them,” said PhD candidate Dalton Leprich, first author of the ISME Journal study. “While it’s not as big of an impact as what humans are doing to the environment, it is a flux of CO2 into the atmosphere that we didn’t know about. These numbers should help us home in on that global carbon budget.”

Leprich’s team started by studying sulphur-oxidising bacteria, which use sulphur as their energy source. The bacteria are found in methane seeps – areas of the ocean floor where methane seepage occurs – which develop unique reef-like topographies due to reactions between methane and seawater. Methane seeps contain limestone formations containing huge amounts of carbon; sulphur-oxidising microbes colonise the surfaces of these formations.

The researchers noticed patterns of corrosion and holes in limestone samples collected from the Del Mar East Methane Seep Field. They used bioreactors which simulate seep conditions to investigate the rates of dissolution associated with the sulphur-oxidising bacteria; their results showed that these bacteria are capable of dissolving limestone, even under well-buffered marine conditions. In the process, they release carbon trapped in the rocks.

In the process of oxidising sulphur, the bacteria cause an acidic reaction which dissolves the rocks, releasing the trapped carbon.

“You can think of this like getting cavities on your teeth. Your tooth is a mineral. There are bacteria that live on your teeth and your dentist will typically tell you that sugars are bad for your teeth,” Leprich explained. “Microbes are taking those sugars and fermenting them, and that fermentation process is creating acid, and that will dissolve away at your teeth. It’s a similar process to what’s happening with these rocks.”

The researchers plan to test this effect on different mineral types.

In addition to identifying a previously unknown source of carbon, contributing towards more accurate estimates of the amount of carbon dioxide entering the atmosphere, the University of Minnesota team’s findings could help researchers use distinct dissolution features caused by bacteria, such as holes and crevices, to search for evidence of life on other astronomical bodies.

“These findings are but one of the many examples of the important and understudied role that microbes play in mediating the cycling of elements on our planet,” said Professor Jake Bailey, an expert in microbial ecologist at the university’s Department of Earth and Environmental Sciences.