Microbes can grow on nitric oxide: What this means for the environment

A concept image of nitric oxide
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A new study by the scientist Boran Kartal and colleagues has given a new insight into the microbial transformations of nitric oxide.

According to the Max Planck Institute for Marine Biology, long before oxygen was on the Earth, nitric oxide was available as a high-energy oxidant and may have played a fundamental role in the emergence and evolution of life on Earth.

What is nitric oxide?

Nitric oxide is important for all living things. It is also highly toxic, and in our environment, it is used as a signalling molecule to deplete the ozone layer as the precursor to nitrous oxide (N2O), the greenhouse gas.

Can organisms use NO to grow?

A major unanswered scientific question about nitric oxide (NO) has been whether organisms can use it to grow.

There has been no microbe growing on NO found until now. Kartal and his colleagues from Radboud University, the Netherlands have discovered that the anaerobic ammonium-oxidizing (anammox*) bacteria directly use NO to grow.

The microorganisms couple ammonium oxidation to NO reduction, producing nothing but dinitrogen gas (N2) in the process. Kartal explained: “In this way, anammox bacteria reduce the amount of NO available for N2O production, and reduce the amount of released greenhouse gas. Our work is interesting in understanding how anammox bacteria can regulate N2O and NO emissions from natural and man-made ecosystems, such as wastewater treatment plants, where these microorganisms contribute significantly to N2-release to the atmosphere.”

What does this mean for emissions and the environment?

Kartal concludes: “These findings change our understanding of the earth’s nitrogen cycle. Nitric oxide has been primarily thought of as a toxin, but now we show that anammox bacteria can make a living from converting NO to N2. Anammox, a globally important microbial process of the nitrogen cycle relevant for the earth’s climate, does not work the way we assumed it did.”

The study is published in Nature Communications.

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