Marine bacteria may be the dominant force responsible for carbon sequestration in the ocean according to a study published in Nature Communications. The findings suggest that these bacteria play a key role in converting simple organic molecules into structurally complex organic matter that is resistant to degradation.

Marine phytoplankton draw carbon dioxide down from the atmosphere and, via photosynthesis and respiration, convert it into a large reservoir of organic carbon, collectively known as dissolved organic matter (DOM). The fate of this DOM is dependent on how difficult to break down it is. DOM that is easily broken down will be recycled within the marine ecosystem, whereas refractory (difficult to break down) DOM, and the carbon it contains, will be locked away for thousands of years. Bacteria are thought to play a role in this sequestration, but the chemical complexity of bacterially modified DOM and its role in the global carbon cycle is not well constrained.

Oliver Lechtenfeld and colleagues use bioassay experiments and ultra-high resolution metabolic profiling to analyse the chemical complexity of DOM, following modification by marine bacteria. The authors conduct a 29-day incubation of coastal seawater microbes mixed with carbon sources and inorganic nutrients, and show that marine bacteria can rapidly convert relatively simple organic molecules into complex molecules that are very difficult to break down. While the authors’ experiment was conducted in the lab, their findings show that bacterial DOM is similar in chemical composition and structural complexity to DOM commonly found in seawater, which suggests a key role for marine bacteria in sequestration of organic carbon.