Deep below the sediment surface in coastal environments, microbes are using tiny conductive particles—like natural “electric wires” – to team up and produce methane, a potent greenhouse gas. A new study published in Nature Communications and led by researchers at the University of Southern Denmark, in collaboration with researchers at Aarhus University, uncovers novel lineages of microorganisms that rely on conductive particles to convert organic carbon to methane, a process that could influence global carbon cycling.
Conductive particles occur naturally in sediments, for example iron oxides such as magnetite, and can enter sediments through human activities, such as chars from forest fires, or soot from industrial pyrolysis. These particles, or their analogues, have been shown to promote methane production in both laboratory partnerships and natural communities. However, it remained unclear which microorganisms are responsible in natural environments and how they interact via conductive particles.
The authors had previously shown that a bacterial-archaeal partnership from coastal sediments was not just promoted by conductive particles, but required conductive particles to convert a simple organic compound, acetate, to methane. A decade ago, they collected sediment samples from the coastal zone of the northern Baltic. They then found that in the laboratory, these methane-producing communities could be propagated only in the presence of conductive particles. However, without genome sequences for the key players, the identity of the partners, and the mechanism by which they collaborate on conductive particles, remained a mystery.
Now, by reconstructing genomes from these consortia bound to conductive particles, the team discovered that the key bacterium belonged to a new genus of bacteria, which they named Candidatus Geosyntrophus acetoxidans because it is a syntrophic bacterium that oxidizes acetate. The partner methanogen was a new species of Methanosarcina that relies on electrons from its partner (received via the conductive particles) to reduce carbon dioxide to methane. This process is known as conductive particle-obligate syntrophic acetate oxidation, and this environmental consortium is the only described example of this type.
A microbial power grid
Unlike traditional microbial partnerships, where cells exchange small molecules or must touch to exchange electrons directly, this partnership uses the conductive particles as a “shared electrical grid”, allowing them to collaborate even when physically separate.
“This is like finding a hidden network of partners wired by the conductive grains in the seafloor”, said Amelia-Elena Rotaru, senior author of the study and group leader at the University of Southern Denmark. ”It shows that we have been missing an important group of climate-relevant microorganisms and a mechanism by which they can drive methane production in sediments”.
The two cell types do not need to be near one another, and high-resolution imaging showed that they both “plug” into the conductive particle to exchange electrons. “In this community, electrons don’t have to move from cell to cell by direct contact—the particles in the environment serve as the electron transfer conduit”, said Amelia-Elena Rotaru.
New microorganisms—found by sequencing genomes of coastal environmental consortia
In this new study, the team reconstructed genomes from this conductive-particle-dependent consortium, which was propagated in the laboratory for many generations over the course of 10 years.
They discovered that the key player was a previously uncharacterized bacterium, Ca . Geosyntrophus acetoxidans. This bacterium is the first cultured relative of a previously undescribed genus.
Genomic analysis showed that it contains a complete pathway for the uptake and oxidation of acetate, as well as a suite of genes associated with extracellular electron transfer, including multiheme cytochromes and conductive pili. The genes for this electron transfer machinery showed very little similarity to those of other bacterial lineages capable of extracellular electron transfer. This bacterium releases electrons onto the conductive particle on which it resides. The partner methanogen then receives electrons from the conductive particles on which it also resides. The methanogen was a new species of Methanosarcina , a globally widespread group of methanogens. It had its own multiheme cytochrome on the cell surface, which is known to facilitate electron uptake from insoluble sources outside the cell, and a full CO 2 -reduction methanogenesis pathway.
“The exciting part is that this wasn’t just ‘we detected a new group of organisms from the environment’,” said Danijel Jovicic, co-lead author. “We can now link a specific, previously uncharacterized bacterium and methanogen to an electron-transfer partnership that ends in methane production—and we can see the molecular machinery for acetate-oxidation, methane-formation and interspecies electron-transport in the genomes.”
“Our results show a mechanism that could lead to greenhouse gas emissions in environments where conductive particles accumulate, and that is something climate and environmental research should also account for.” Rotaru said.
This work was supported by a Danish Research Council grant awarded to Amelia-Elena Rotaru (PI, SDU) and Bo Barker Jørgensen (Co-PI, AU), and by a European Research Council Consolidator Grant awarded to Amelia-Elena Rotaru at the University of Southern Denmark.
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Candidatus Geosyntrophus acetoxidans . The name reflects both where this microbe lives and how it survives. ‘Candidatus’ means it has not been grown alone in the lab. ‘Geosyntrophus’ comes from the Greek words for earth or ground (Gē), and for living together or feeding together ( syntrophos ), reflecting that this Earth microbe lives in metabolic partnership with others. The species name ‘ acetoxidans’ refers to its ability to oxidize acetate.
Extracellular electron transfer is a way some microorganisms ‘respire’ without oxygen. In microorganisms that ‘respire’ oxygen, electrons taken from food are passed through a chain of membrane proteins inside the cell to oxygen. This ultimately gives the cell a form of energy it can use for work inside the cell. A similar process also happens in our own cells, in the mitochondria. Some microbes, that live without oxygen do something different. Instead of passing electrons to oxygen inside the cell, they move them out of the cell through specialized proteins on their cell surface and transfer them to minerals, conductive particles or even partner cells nearby. This process is called extracellular electron transfer.
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Paper details:
Title: Genome-centric metagenomics reveals novel electroactive syntrophs in a conductive particle-dependent consortium from coastal sediments.
Authors: Danijel Jovicic, Konstantinos Anestis, Jacek Fiutowski, Bo Barker Jørgensen, Kasper Urup Kjeldsen, Amelia‑Elena Rotaru.
Affiliations: University of Southern Denmark; Aarhus University; SDU NanoSYD (Mads Clausen Institute).
Corresponding author: Amelia‑Elena Rotaru (arotaru@biology.sdu.dk).
Nature Communications
Experimental study
Cells
Genome-centric metagenomics reveals electroactive syntrophs in a conductive particle-dependent consortium from coastal sediments
24-Mar-2026