Researchers at the University of Vienna have discovered a new type of microbe that oxidizes toxic sulfide using iron minerals, potentially helping to prevent oceanic dead zones. These MISO bacteria convert sulfide into sulfate for energy, reshaping understanding of global sulfur and iron cycles. The findings, published in Nature, highlight microbes' role in maintaining ecological balance.
An international team led by microbiologists Marc Mussmann and Alexander Loy at the University of Vienna has identified microorganisms capable of a novel metabolic process. Dubbed MISO bacteria—for Microbial Iron oxide respiration coupled to Sulfide Oxidation—these microbes 'breathe' iron minerals by oxidizing hydrogen sulfide, a toxic gas produced in oxygen-poor environments like marine sediments and wetland soils.
Previously, scientists believed the reaction between hydrogen sulfide and iron(III) oxide minerals, or rust, occurred only chemically, forming elemental sulfur and iron monosulfide. However, the researchers demonstrated that microbes actively harness this reaction for growth, producing sulfate directly and bypassing intermediate steps in the sulfur cycle. 'We show that this environmentally important redox reaction is not solely chemical,' says 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.'
In laboratory experiments, the MISO process proved faster than its chemical counterpart, suggesting microbes drive this transformation in nature. '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.
The discovery links sulfur, iron, and carbon cycles in oxygen-deprived habitats, influencing greenhouse gas production. Diverse bacteria and archaea possess the genetic capacity for MISO and are found in marine sediments, wetlands, and human-made environments. The study estimates this activity accounts for up to 7% of global sulfide oxidation to sulfate, fueled by iron from rivers and glaciers. Supported by the Austrian Science Fund (FWF), the research was published in Nature on November 9, 2025, by lead author Song-Can Chen and colleagues (DOI: 10.1038/s41586-025-09467-0).
'This discovery demonstrates the metabolic ingenuity of microorganisms and highlights their indispensable role in shaping Earth's global element cycles,' concludes Alexander Loy.