‘Iron-breathing’ microbe which eliminate toxic sulfide from Earth discovered by scientists
Newly discovered microorganisms known as MISO bacteria “breathe” iron minerals by oxidizing hydrogen sulfide, a toxic gas found in oxygen-free environments. The findings were published in Nature on August 27, 2025.
The research team found that the reaction between hydrogen sulfide and solid iron minerals is not only chemical but also biological. Microbes living in marine sediments and wetlands remove harmful sulfide from their environment and use it to fuel their growth.
Also read: How can AI help understand gut bacteria?
“We have shown that this environmentally important redox reaction is not just chemical,” explains Alexander Loy, leader of the CeMESS research group at the Center for Microbiology and Environmental Systems Science at the University of Vienna. “Microorganisms can also use it to grow.”
The newly discovered microbial energy metabolism, called MISO, combines the reduction of iron(III) oxide with the oxidation of sulfur. Unlike chemical reactions, MISO produces sulfate directly, bypassing intermediate steps in the sulfur cycle.
MISO bacteria may help prevent dead zones in the ocean
This natural mechanism could help limit the spread of oxygen-depleted “dead zones” in oceans and lakes where marine life cannot survive.
CeMESS senior scientist Marc Mussmann adds: “MISO bacteria remove toxic sulphide and can help prevent the expansion of so-called ‘dead zones’ in aquatic environments while fixing carbon dioxide for growth, as in plants.”
Biogeochemical cycles regulate Earth’s climate and element movement
The movement of elements such as carbon, nitrogen, sulfur, and iron in Earth systems is governed by biogeochemical cycles. These cycles involve chemical reactions called redox reactions that enable the transfer of elements between the atmosphere, oceans, soil, rocks, and living organisms.
Microbes are vital to these global processes, using compounds such as sulfur and iron to produce energy in ways similar to how humans use oxygen. Sulfur and iron are particularly important for microorganisms that live in low-oxygen environments such as the seabed or wetlands.
When microbes consume sulfur, they often simultaneously change the chemical form of iron. This link between sulfur and iron cycles affects nutrient flow and the production or breakdown of greenhouse gases such as carbon dioxide and methane.
Also read: NASA discovers super bacteria by chance…
Microbial process faster than chemical reactions in laboratory tests
In laboratory growth experiments with a cultivated MISO bacterium, the researchers showed that the enzymatically catalyzed reaction was faster than the equivalent chemical reaction. This suggests that microbes are the primary drivers of this process in nature.
“A variety of bacteria and archaea have the genetic capacity for MISO, and they are found in a wide variety of natural and human-made environments,” explains Song-Can Chen, lead author of the study.
MISO accounts for 7% of global sulfide oxidation
In marine sediments, MISO can account for up to 7% of the global oxidation of sulfide to sulfate due to significant fluxes of reactive iron from rivers and melting glaciers to the oceans.
Hydrogen sulfide production occurs in anoxic habitats
In anoxic habitats such as marine sediments, wetlands, and underground aquifers, specialized microbes produce hydrogen sulfide, a toxic gas with a distinctive odor reminiscent of rotten eggs.
The interaction between sulfur and solid iron(III) oxide minerals (such as rust) helps regulate how much sulfur accumulates in these environments. Until now, scientists believed that this process was entirely abiotic, driven solely by chemical reactions that produced compounds such as elemental sulfur and iron monosulfide (FeS), the black mineral responsible for the dark coloration often seen in low-oxygen coastal or beach sediments.
The findings of the University of Vienna team, supported by the Austrian Science Fund (FWF) as part of the ‘Microbiomes Strengthen Planetary Health’ Cluster of Excellence, reveal a previously unknown biological mechanism linking the cycle of sulfur, iron and carbon in anoxic environments.
“This discovery demonstrates the metabolic creativity of microorganisms and highlights their indispensable role in shaping the Earth’s global elemental cycles,” concludes Alexander Loy.
