Discover how newly found MISO bacteria “breathe” iron rust to eliminate toxic hydrogen sulphide. Learn about this unique metabolism that helps clean our oceans and may prevent the spread of dead zones.

A group of scientists from around the world, led by microbiologists Marc Mussmann and Alexander Loy from the University of Vienna, has uncovered a new method that some microbes use to generate energy. These microscopic organisms, known as MISO bacteria, have the ability to “breathe” iron minerals. This means they use rust in a way that is similar to how humans use oxygen. As a result, they also help eliminate a harmful gas called hydrogen sulphide, which is often present in areas where there is little or no oxygen, such as marine sediments and wetlands.

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Their findings, published in the journal Nature, show that what was previously thought to be a simple chemical reaction between sulphide and iron is actually a biological process carried out by living microbes. This unique form of metabolism could be essential in cleaning up the oceans and reducing the expansion of “dead zones,” which are areas where most marine life cannot survive due to a lack of oxygen.

How Microbes Keep Earth’s Chemistry in Balance

On Earth, elements such as carbon, nitrogen, sulphur, and iron move continuously between the air, water, soil, and living organisms. This movement, known as biogeochemical cycling, occurs through a series of chemical reactions that either add or remove oxygen from these elements. These reactions are crucial for sustaining life because they help regulate greenhouse gases such as carbon dioxide and methane, which in turn influence the Earth’s climate.

Microorganisms play a central role in these cycles. They carry out most of the reactions that maintain Earth’s chemical balance. Just as humans rely on oxygen to convert food into energy, microbes can use other substances like sulphur or iron for their own growth.

In places where there is little or no oxygen, such as the seafloor, wetlands, or underground soil layers, these microbes use sulphur and iron instead. Sulphur can exist in many forms, including as a gas in the air, dissolved in seawater, or stored in rocks and minerals. Iron, on the other hand, changes its chemical state depending on the amount of oxygen available. When microbes process sulphur, they often alter iron as well, creating a direct link between the two elements.

This connection influences how nutrients flow through the environment and how greenhouse gases are either produced or removed. Understanding how microbes handle sulphur and iron can help scientists better predict how ecosystems react to pollution and climate change.

The Microbes That Eat Sulphide and “Breathe” Iron

In oxygen-poor environments, some microbes produce hydrogen sulphide, a gas with a strong, unpleasant smell often associated with the odour of rotten eggs. Typically, this gas reacts with iron minerals (essentially rust) to form dark compounds like iron monosulphide, which is responsible for the black colour of mudflats and some beach sands. Scientists previously believed that this reaction was purely a chemical process and did not involve living organisms.

However, the research team from Vienna has now demonstrated that this process is also driven by microbes. The MISO bacteria use hydrogen sulphide as an energy source and transfer electrons to iron minerals, effectively “breathing” rust. This biological process, called MISO metabolism, links the oxidation of sulphide (the removal of its electrons) to the reduction of iron (the addition of electrons).

What makes MISO bacteria unique is that they bypass the usual steps of the sulphur cycle. Instead of forming intermediate compounds, these bacteria convert sulphide directly into sulphate, a much less harmful substance. In doing so, they not only eliminate toxic sulphide but also absorb carbon dioxide from their surroundings, using it for their growth, similar to how plants use carbon dioxide.

According to the researchers, this ability may help prevent or slow the spread of “dead zones” in oceans and lakes. These areas are often the result of pollution and a lack of oxygen, making it impossible for fish and other marine life to survive.

A Widespread and Powerful Natural Process

Lab experiments showed that the MISO reaction occurs much more quickly when microbes are involved compared to when it happens purely through chemical means. The researchers estimate that microbial MISO activity in the world’s oceans could be responsible for up to 7% of all sulphide oxidation to sulphate globally. This is supported by the continuous supply of iron entering the oceans through rivers, dust, and melting glaciers.

This discovery not only fills in a missing link between the cycles of sulphur, iron, and carbon but also highlights the creativity and adaptability of microbes. They play vital roles in maintaining Earth’s systems, often in ways that are only now beginning to be understood.