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Microbes feed on iron: New study reveals how they do it

Pipelines, sprinklers, and other infrastructure in oxygen-free environments are vulnerable to microbially induced corrosion (MIC)—a process where microorganisms degrade iron-based structures, potentially leading to costly damages or even collapses.

Unlike rust, which is caused by a chemical reaction with oxygen, MIC occurs in oxygen-free environments. The microbes responsible thrive on the iron itself, producing a destructive reaction that damages the material. This kind of corrosion costs industries billions of dollars annually, particularly in sectors such as oil and gas. Identifying and preventing the microbial activity behind the corrosion is therefore of importance.

Now, microbiologists, Ph.D. Satoshi Kawaichi and Professor, Dr. Amelia-Elena Rotaru from University of Southern Denmark have uncovered new details about how one microbial strain of the species Methanococcus maripaludis corrodes iron in an extremely efficient way. The study is in npj Biofilms and Microbiomes.

The study refutes the long-standing belief that these microbes release enzymes into the environment to corrode iron and have them produce nutrients for the microbe's growth. Instead, the researchers show that the microbes cling directly to the iron surface, using sticky enzymes on their cell walls to extract what they need without wasting energy on releasing enzymes that may not reach the iron surface.

Once attached to the iron surface, the microbe initiates corrosion, quickly developing a black film on the material's surface.

"The microbes will quickly create pits under this black film, and within a few months, significant damage will occur. I would say that 5-gram iron granules visible with the naked eye are bio-deteriorated to a black powder in a month or two," said Kawaichi.

According to the researchers, microbial adaptation like this is an example of how microbes can learn to thrive in human-made environments. In this case, Methanococcus maripaludis, has learned to survive on and efficiently get energy from iron structures.

Such microbial adaptation poses not only a financial burden but also an environmental one. "These microbes are methanogenic, meaning they produce methane. Methane is a potent greenhouse gas, so it does cause some concern that microbes adapting to human-made, built environments produce methane more effectively. These new adaptations may spur increases in methane emissions," said Rotaru.

Methane-producing microbes also thrive on a variety of mineral particles that are being released to the natural environment by climate change and other anthropogenic activities. Such particles come from industry, agriculture, forest fires, river runoffs, melting glaciers, etc., and they may promote the activity of certain methane-producing microbes.

Currently, members of Rotaru's research group are investigating glacier melt particles from Greenland to see how the particles influence methane emissions to the atmosphere.