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<a href = "https://3c1703fe8d.site.internapcdn.net/newman/gfx/news/hires/2019/microbescang.jpg" title = "One of the bioreactors that Kartal and his colleagues used to make push cells from K. stuttgartiensis in the laboratory. The bright red color is due to the presence of cytochrome c proteins containing iron in the cells. Anammox bacteria are filled with cytochrome c-like proteins, including enzymes that perform the key reactions of the anammox process, making the cells remarkably red. Credit: Boran Kartal ">
One of the bioreactors used by Kartal and his colleagues to grow K. stuttgartiensis in the laboratory. The bright red color is due to the presence of cytochrome c proteins containing iron in the cells. Anammox bacteria are filled with cytochrome c-like proteins, including enzymes that perform the key reactions of the anammox process, making the cells remarkably red. Credit: Boran Kartal
Nitric oxide is a fascinating and versatile molecule, important for all living things as well as for our environment. It is highly reactive and toxic. it is used as a signaling molecule; it depletes the layer of ozone in the atmosphere of our planet; and it is the precursor of nitrous oxide (N2O) Nitrogen oxides are also pollutants released by exhaust gases, for example from combustion engines in cars, and are harmful to human health.
Surprisingly, long before there was oxygen on Earth, nitric oxide was available as a high energy oxidant and could have played a fundamental role in the world. emergence and evolution of life on Earth. A study by Boran Kartal, scientist Max-Planck, and his colleagues now published in Nature Communications brings a new light on the microbial transformations of this molecule.
Yes, they can – with implications for our climate
A major question about nitric oxide has remained unanswered so far: can organisms use it to grow?
One could think, says Kartal, "that nitric oxide exists since the onset of life on Earth." However, no growing microbe on NO has been found – until now. Kartal and his colleagues at Radboud University in the Netherlands have now discovered that anaerobic bacteria oxidizing ammonium (anammox) directly use NO to multiply. These microorganisms couple in detail the oxidation of ammonium to the reduction of NO, producing only dinitrogen gas (N2) In the process.
The latter, the only production of N2– is particularly intriguing: some microbes convert NO to nitrous oxide (N2O), which is a powerful greenhouse gas. NOT2on the contrary, is harmless. Thus, each molecule of NO transformed into N2 instead of N2O is one less molecule contributing to climate change. "In this way, anammox bacteria reduce the amount of NO available for N2Kartal explains: "Our work is interesting to understand how the anammox bacteria can regulate the N2O and NO emissions from natural and man-made ecosystems, such as wastewater treatment plants, where these microorganisms contribute significantly to N2-to release to the atmosphere. "
<a href = "https://3c1703fe8d.site.internapcdn.net/newman/gfx/news/hires/2019/1-microbescang.jpg" title = "Kuenenia stuttgartiensis, seen here under the transmission electron microscope, is an anammox model microorganism, which develops as individual cells. It is a species of freshwater that is also found in sewage treatment plants. Credit: Laura van Niftrik ">
Rethinking the nitrogen cycle
Nitric oxide is a central molecule in the global nitrogen cycle. "These findings are changing our understanding of the Earth's nitrogen cycle.Nitric Oxide has been primarily considered a toxin, but we are now showing that the Anammox bacteria can make a living by converting NO to N2"says Kartal.
This study raises new questions. "Anammox, a microbial process of the important nitrogen cycle for the climate that plays an important role for the planet's climate, does not work as we had supposed." In addition, other microbes than those studied here could also directly use NO. Anammox bacteria are present all over the planet. "In this sense, anammox microbes growing on nitric oxide could also be practically everywhere," says Kartal.
One answer, many new questions
Today, Kartal and his group at the Max Planck Institute in Bremen are exploring different ecosystems around the world in search of microorganisms specializing in the conversion of nitric oxide. They want to better understand how microbes use NO in environments with and without oxygen. This will likely open the way to the discovery of new enzymes involved in the transformation of nitric oxide. "Basically, we want to understand how organizations can make a living with NO."
What is the anammox?
Anammox, abbreviation for anaerobic ammonium oxidation, is a microbial process of global importance to the nitrogen cycle. It takes place in many natural and artificial environments. In this process, the nitrite and ammonium ions are converted directly into dinitrogen, water and nitrate.
Anammox is responsible for about 50% of the N2 gas produced in the oceans. It thus eliminates large amounts of bioavailable nitrogen in the seas. This nutrient nitrogen is then no longer available for other organisms; In this way, the anammox can control the primary productivity of the oceans.
The anammox process is also interesting for the treatment of wastewater. The elimination of nitrogen compounds with the help of anammox bacteria is significantly cheaper than traditional methods and reduces greenhouse gas emissions, the CO2.
Explore further:
Bacteria forge nitrogen from nitric oxide: scientists discover the key path of the nitrogen cycle
More information:
Ziye Hu et al. Anaerobic ammonium oxidation dependent on nitric oxide. Nature Communications. DOI: 10.1038 / s41467-019-09268-w
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