Scientists led by microbiologists from the University of Vienna have uncovered a previously unknown microbial metabolism in which “MISO” bacteria breathe iron minerals by oxidizing toxic sulfide.
Credit: SciTechDaily.com
Microbiologists discover bacteria that eliminate toxic sulfide and use iron minerals to grow.
An international group of researchers led by microbiologists Marc Mussmann and Alexander Loy at the University of Vienna has identified a previously unknown form of microbial metabolism. The newly discovered microorganisms, known as MISO bacteria, “breathe” iron minerals by oxidizing toxic sulfide.
The team found that the reaction between hydrogen sulfide and solid iron minerals is not purely chemical but also biological. In this process, microbes living in marine sediments and wetlands remove harmful sulfide from their surroundings and use it to fuel their growth. This natural mechanism may help limit the spread of oxygen-depleted “dead zones” in oceans and lakes. The findings were published in Nature.
Credit: Alexander Loy
The global element cycles
The movement of elements such as carbon, nitrogen, sulfur, and iron through Earth’s systems is governed by a set of processes known as biogeochemical cycles. These cycles involve chemical reactions called redox (reduction and oxidation) reactions that transfer these elements between the atmosphere, oceans, soil, rocks, and living organisms. They play a major role in regulating Earth’s climate by controlling greenhouse gas levels and maintaining temperature balance.
The global element cycles
The movement of elements such as carbon, nitrogen, sulfur, and iron through Earth’s systems is governed by a set of processes known as biogeochemical cycles. These cycles involve chemical reactions called redox (reduction and oxidation) reactions that transfer these elements between the atmosphere, oceans, soil, rocks, and living organisms. They play a major role in regulating Earth’s climate by controlling greenhouse gas levels and maintaining temperature balance.
Credit: Alexander Loy
Microbes are vital to these global processes, using compounds like sulfur and iron to produce energy in ways similar to how humans use oxygen. Sulfur and iron are especially important for microorganisms that live in low-oxygen environments like the seafloor or wetlands. Sulfur can exist as a gas, a dissolved compound in seawater, or a mineral in rocks, while iron changes form depending on oxygen availability.
When microbes consume sulfur, they often change the chemical form of iron at the same time. This connection between the sulfur and iron cycles affects nutrient flow and the production or breakdown of greenhouse gases such as carbon dioxide and methane. Studying these links helps scientists better predict how ecosystems react to human activities, climate shifts, and pollution.
Microbes are vital to these global processes, using compounds like sulfur and iron to produce energy in ways similar to how humans use oxygen. Sulfur and iron are especially important for microorganisms that live in low-oxygen environments like the seafloor or wetlands. Sulfur can exist as a gas, a dissolved compound in seawater, or a mineral in rocks, while iron changes form depending on oxygen availability.
When microbes consume sulfur, they often change the chemical form of iron at the same time. This connection between the sulfur and iron cycles affects nutrient flow and the production or breakdown of greenhouse gases such as carbon dioxide and methane. Studying these links helps scientists better predict how ecosystems react to human activities, climate shifts, and pollution.
Breathing iron minerals to detoxify Sulfide
In oxygen-free habitats such as marine sediments, wetlands, and underground aquifers, specialized microbes produce hydrogen sulfide, a toxic gas with a distinct odor reminiscent of rotten eggs. The interaction between sulfide and solid iron(III) oxide minerals—like rust—helps regulate how much sulfide accumulates in these settings. Until now, scientists believed this process was entirely abiotic, driven only by chemical reactions that produce compounds like elemental sulfur and iron monosulfide (FeS), the black mineral responsible for the dark coloration often seen in low-oxygen coastal or beach sediments.
Credit: Alexander Loy
“We show that this environmentally important redox reaction is not solely chemical,” explains Alexander Loy, research group leader at CeMESS, the Centre for Microbiology and Environmental Systems Science at the University of Vienna. “Microorganisms can also harness it for growth.”
The newly discovered microbial energy metabolism, shortly termed MISO, couples the reduction of iron(III) oxide with the oxidation of sulfide. Unlike the chemical reaction, MISO directly produces sulfate, effectively bypassing intermediate steps in the sulfur cycle. “MISO bacteria remove toxic sulfide and may help prevent the expansion of so-called “dead zones” in aquatic environments, while fixing carbon dioxide for growth – similar to plants,” adds Marc Mussmann, senior scientist at CeMESS.
“We show that this environmentally important redox reaction is not solely chemical,” explains Alexander Loy, research group leader at CeMESS, the Centre for Microbiology and Environmental Systems Science at the University of Vienna. “Microorganisms can also harness it for growth.”
The newly discovered microbial energy metabolism, shortly termed MISO, couples the reduction of iron(III) oxide with the oxidation of sulfide. Unlike the chemical reaction, MISO directly produces sulfate, effectively bypassing intermediate steps in the sulfur cycle. “MISO bacteria remove toxic sulfide and may help prevent the expansion of so-called “dead zones” in aquatic environments, while fixing carbon dioxide for growth – similar to plants,” adds Marc Mussmann, senior scientist at CeMESS.
Credit: Alexander Loy
A globally important microbial process that outpaces chemistry
In laboratory growth experiments with a cultivated MISO bacterium, the researchers demonstrated that the enzymatically catalyzed reaction is faster than the equivalent chemical reaction. This suggests that microbes are the primary drivers of this process in nature.
“Diverse bacteria and archaea possess the genetic capacity for MISO,” explains Song-Can Chen, lead author of the study, “and they are found in a wide range of natural and human-made environments.” In marine sediments, MISO could account for up to 7% of global sulfide oxidation to sulfate, driven by the substantial flux of reactive iron from rivers and melting glaciers into the oceans.
The findings of the University of Vienna team, which is supported by the Austrian Science Fund (FWF) as part of the ‘Microbiomes Drive Planetary Health’ Cluster of Excellence, reveal a previously unknown biological mechanism that links sulfur, iron, and carbon cycling in oxygen-free environments.
“This discovery demonstrates the metabolic ingenuity of microorganisms and highlights their indispensable role in shaping Earth’s global element cycles.” Alexander Loy concludes.
A globally important microbial process that outpaces chemistry
In laboratory growth experiments with a cultivated MISO bacterium, the researchers demonstrated that the enzymatically catalyzed reaction is faster than the equivalent chemical reaction. This suggests that microbes are the primary drivers of this process in nature.
“Diverse bacteria and archaea possess the genetic capacity for MISO,” explains Song-Can Chen, lead author of the study, “and they are found in a wide range of natural and human-made environments.” In marine sediments, MISO could account for up to 7% of global sulfide oxidation to sulfate, driven by the substantial flux of reactive iron from rivers and melting glaciers into the oceans.
The findings of the University of Vienna team, which is supported by the Austrian Science Fund (FWF) as part of the ‘Microbiomes Drive Planetary Health’ Cluster of Excellence, reveal a previously unknown biological mechanism that links sulfur, iron, and carbon cycling in oxygen-free environments.
“This discovery demonstrates the metabolic ingenuity of microorganisms and highlights their indispensable role in shaping Earth’s global element cycles.” Alexander Loy concludes.
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