“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.” With these words, Boran Kartal from the Max Planck Institute for Marine Microbiology in Bremen sums up a surprising discovery by the microbiologists: Together with colleagues, the Bremen researchers have for the first time discovered an anaerobic ammonium-oxidizing (short: "Anammox") bacterium that uses nitric oxide ("NO") to grow. If such bacteria were widespread, it could change our understanding of the global nitrogen cycle and be relevant for climate models.

Impact on climate and ozone layer

Nitric oxide is harmful to many organisms, it attacks the ozone layer, and it is a precursor of nitrous oxide (N2O), a significant greenhouse gas. At the same time, NO is a very reactive and energy-rich gas that has existed since the early days of the Earth. Microbiologists have therefore been surprised that no microbe has been discovered that uses this molecule for its growth. Only microorganisms that convert NO into nitrous oxide are known.

Kuenenia stuttgartiensis forms molecular nitrogen

In the specialist journal "Nature Communications", the Max Planck researchers and scientists from the Dutch University of Radboud now report on the anammox bacterium Kuenenia stuttgartiensis, which actually needs nitric oxide to live. If no nitrite is available for the microorganism, it couples the oxidation of ammonium to the reduction of nitrogen monoxide and thus produces molecular nitrogen (N2). In contrast to nitrous oxide, N2 is harmless to health, the climate and the ozone layer. Because this reaction results in less NO being available to be converted into nitrous oxide, these bacteria reduce the number of molecules that warm the climate.

Search for organisms with the same ability

"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," Kartal explains the relevance of the discovery. Since anammox bacteria can be found all over the world, "in this sense, the anam­mox mi­crobes grow­ing on nitric ox­ide could also be ba­sic­ally every­where". The search for them is next on the agendy of the microbiologist and his group.

bl/um