Paddy soil bacterium runs on electricity and converts CO2 into acetate
Most bacteria generate energy by running chemical reactions entirely inside their cells. A smaller group has evolved something stranger: the ability to move electrons across their membranes and exchange them directly with external surfaces - minerals, electrodes, or other cells. This capacity, called extracellular electron transfer, gives those microbes a kind of electrical literacy that researchers have been trying to harness for carbon conversion and clean energy applications.
A study published in Energy and Environment Nexus describes a newly isolated member of this group. The sulfate-reducing bacterium Fundidesulfovibrio terrae, extracted from paddy soil in China, stands out for a property not commonly documented: it can perform extracellular electron transfer in both directions. It can push electrons out to external surfaces and pull electrons in from them - a bidirectional capability that makes it an unusual candidate for driving carbon chemistry with electrical input.
What the bacterium can do
In laboratory experiments, F. terrae transferred electrons to iron minerals without requiring chemical mediators, reducing iron compounds with an efficiency exceeding 60%. Electrochemical measurements confirmed both directions of electron flow: the bacterium formed stable biofilms on electrode surfaces and could either donate or accept electrons depending on the electrical conditions.
The more striking result came when the researchers supplied the bacterium with electrons from an electrode and carbon dioxide as its sole carbon source. Under those conditions, F. terrae fixed the CO2 into acetate - a two-carbon organic acid used as a feedstock in chemical manufacturing - via the Wood-Ljungdahl pathway. This ancient carbon fixation route is one of the most energy-efficient available to microorganisms. The cultures produced acetate at concentrations exceeding 11 millimolar, demonstrating that meaningful organic conversion was occurring.
"This microorganism demonstrates an exceptional ability to harvest energy directly from electrical sources and channel it into carbon metabolism," the corresponding author said. "Its metabolic flexibility provides a new biological platform for linking renewable electricity with carbon recycling."
The molecular wiring
Genomic and biochemical analysis identified the structural components enabling this electrical behavior. Specialized proteins called c-type cytochromes serve as molecular conduits, shuttling electrons across the cell membrane. The bacterium also appears to produce conductive pili - thread-like surface structures that function as microscopic wires, extending electrical connectivity beyond the cell wall to external surfaces.
These structural features connect F. terrae to a broader family of electroactive microorganisms, including the well-studied Geobacter and Shewanella genera, though the bidirectional character of its electron transfer represents a distinct capability within that group.
Potential applications and significant remaining distance
Microbial electrosynthesis - using electricity to drive microbes to convert CO2 into fuels or chemicals - has attracted interest as a way to store renewable electricity in chemical form while reducing atmospheric carbon. Systems based on this principle could in theory convert excess solar or wind power into acetate, ethanol, or other useful compounds, coupling energy storage with carbon utilization.
F. terrae's combination of properties - bidirectional electron transfer, efficient iron reduction, and acetate production from CO2 and electricity alone - makes it a potentially interesting platform organism for such applications. The acetate it produces can serve directly as a feedstock for further chemical synthesis or as a carbon source for other microorganisms.
Several significant gaps remain. The experiments reported were conducted in controlled laboratory conditions using defined growth media and electrode setups. How the bacterium performs in more complex environments - or in scaled-up systems with industrial-relevant current densities - is not yet known. The acetate concentrations achieved (above 11 millimolar) are measurable but well below what would be needed for cost-competitive chemical production; improving productivity will require engineering of both the biological system and the electrochemical reactor design. The study is a characterization of a newly discovered organism and its capabilities, not a demonstration of an industrial process.
The broader context is that sulfate-reducing bacteria are widespread in soils and sediments and already play important roles in biogeochemical cycling. Finding that some members of this group carry bidirectional electron transfer capabilities suggests there may be other undiscovered electroactive bacteria in environments that have not been systematically screened.