Hidden microbial network could drive methane production in the seafloor

Deep below the surface in coastal sediments, microorganisms use conductive particles as tiny natural “wires” to exchange electrons. This enables them to convert organic carbon into methane in a way not previously documented. The mechanism is described in a new study in Nature Communications (find it here) led by researchers from the University of Southern Denmark in collaboration with Aarhus University.

Conductive particles such as magnetite occur naturally in many coastal sediments, while others enter the environment through forest fires, agriculture or industrial activities. For more than a decade, SDU researchers have studied microbial communities from the northern Baltic Sea that only produce methane when such particles are present. Without these particles, the collaboration between the organisms simply stops.

“In our new study, we show that this electrical interaction forms a kind of microbial “power grid” beneath the seafloor. The grid allows microorganisms to exchange electrons without being in direct contact, revealing a form of cooperation that had not been recognized in natural environments”, said senior author of the study and group leader at Department of Biology, Professor Amelia-Elena Rotaru.

By sequencing genomes from the sediment communities, the researchers identified a new bacterium that oxidizes acetate and releases electrons onto the conductive particles. They named it Candidatus Geosyntrophus acetoxidans, representing a previously undescribed bacterial genus. The organism carries unique genes for extracellular electron transfer, distinguishing it from all known relatives.

The team also found that the partner methanogen is a new species of Methanosarcina, a widely distributed group of methane‑producing archaea. This organism takes up electrons directly from the conductive particles and uses them to convert CO₂ into methane. The two partners attach to the same conductive grains, allowing electron exchange without physical contact. High‑resolution imaging confirmed that both microorganisms are connected through the conductive particles rather than through cell‑to‑cell interactions.

“This makes the consortium the only known example of a conductive particle‑dependent methane‑producing partnership in nature”, said Danijel Jovivic, co-lead author of the study.

Implications for climate and carbon cycling

Coastal sediments are known to be sources of methane, a potent greenhouse gas. The discovery of a new methane‑producing mechanism highlights how conductive particles may shape carbon cycling in ways that have not been included in climate models. Environments with high inputs of such particles may therefore host previously unrecognized methane‑producing communities.

“These microorganisms depend entirely on the conductive network in the sediment. It means we have been missing an important group of climate‑relevant microbes and an important process in methane production”, said Professor Rotaru, adding:

“Because conductive particles are widespread — and in some environments increasing due to human activity — the discovery could have broader implications for understanding natural greenhouse gas emissions”.

The researchers suggest that this mechanism should now be included in studies of carbon turnover and methane formation in coastal ecosystems.