The anaerobic oxidation of ammonia (anammox) is an important pathway in the nitrogen cycle that was only discovered in the 1980s. Currently, scientists estimate that about 50 percent of the nitrogen in the atmosphere is forged by this process. A group of specialized bacteria perform the anammox reaction, but so far scientists have been in the dark about how these bacteria could convert ammonia to nitrogen in the complete absence of oxygen. Now, 25 years after its discovery, they finally solved the molecular mechanism of anammox.
Anammox bacteria are very unusual because they contain an organelle which is a typical eukaryotic feature. Inside this organelle, known as the “anammoxosome”, the bacteria perform the anammox reaction. The membrane of the anammoxosome presumably protects the cells from highly reactive intermediates of the anammox reaction. These intermediates could be hydrazine and hydroxylamine, as microbiologists proposed many years ago. This was very exciting news because the turnover of hydrazine, a very powerful reductant also used as rocket fuel, had never been shown in biology. However, these early experiments were provisional and many open questions remained.
To finally unravel the pathway experimentally was a very difficult enterprise. Marc Strous from the Max Planck Institute in Bremen says: “The anammox organisms are difficult to cultivate because they divide only once every two weeks. Therefore we had to develop cultivation approaches suitable for such low growth rates. Even after 20 years of trials, we can still only grow the organisms in bioreactors and not in pure culture.” In the present study, the researchers make use of the latest innovation in bioreactor technology for anammox cultivation: the membrane bioreactor. In such bioreactors the anammox organisms grow as suspended cells rather than in biofilms on surfaces, and relatively few contaminating organisms are present. The study makes use of protein purification and proteins cannot be effectively purified from biofilms because of the large amount of slime associated with these biofilms.
Another important key to the metabolism was the availability of the genome sequence of one of the best known anammox bacteria, Kuenenia stuttgartiensis. With the knowledge of the genome, the authors knew which proteins could be important. Based on the genome sequence, they could predict that nitric oxide, not hydroxylamine, might be the precursor for hydrazine. With a set of state-of-the art molecular methods the scientists could thus completely unravel the anammox pathway, and unequivocally establish the role of hydrazine and nitric oxide (NO) as intermediates.
“With this significant advance we can finally understand how the nitrogen in the air we breathe is created: from rocket fuel and nitric oxide!” concludes Marc Strous. With the establishment of the prominent role of nitric oxide in both anammox and denitrification, the research also opens a new window on the evolution of the biological nitrogen cycle in the Earth's distant past. Marc Strous explains: ”In the early days in Earth’s history, the nitric oxide accumulated in the atmosphere by vulcanic activity, was presumably the first “deep electron sink” on earth and may so have enabled the evolution of both microbial metabolic pathways anammox and denitrification.”
Institute for Water and Wetland Research, Department of Microbiology, Radboud University, Nijmegen, The Netherlands
Nijmegen Centre for Mitochondrial Disorders, Nijmegen Proteomics Facility, Department of Laboratory Medicine, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
Radboud University, Department of Molecular Biology, Nijmegen Centre for Molecular Life Sciences, Nijmegen, The Netherlands
Delft University of Technology, Department Biotechnology, Delft, The Netherlands
Max Planck Institute for Marine Microbiology, Bremen, GermanyContact
Prof. Dr. Ir. Marc Strous | EurekAlert!
Dispersal of Fish Eggs by Water Birds – Just a Myth?
19.02.2018 | Universität Basel
Removing fossil fuel subsidies will not reduce CO2 emissions as much as hoped
08.02.2018 | International Institute for Applied Systems Analysis (IIASA)
Magnetic resonance imaging, or MRI, is a widely used medical tool for taking pictures of the insides of our body. One way to make MRI scans easier to read is...
At the Hannover Messe 2018, the Bundesanstalt für Materialforschung und-prüfung (BAM) will show how, in the future, astronauts could produce their own tools or spare parts in zero gravity using 3D printing. This will reduce, weight and transport costs for space missions. Visitors can experience the innovative additive manufacturing process live at the fair.
Powder-based additive manufacturing in zero gravity is the name of the project in which a component is produced by applying metallic powder layers and then...
Physicists at the Laboratory for Attosecond Physics, which is jointly run by Ludwig-Maximilians-Universität and the Max Planck Institute of Quantum Optics, have developed a high-power laser system that generates ultrashort pulses of light covering a large share of the mid-infrared spectrum. The researchers envisage a wide range of applications for the technology – in the early diagnosis of cancer, for instance.
Molecules are the building blocks of life. Like all other organisms, we are made of them. They control our biorhythm, and they can also reflect our state of...
University of Connecticut researchers have created a biodegradable composite made of silk fibers that can be used to repair broken load-bearing bones without the complications sometimes presented by other materials.
Repairing major load-bearing bones such as those in the leg can be a long and uncomfortable process.
Study published in the journal ACS Applied Materials & Interfaces is the outcome of an international effort that included teams from Dresden and Berlin in Germany, and the US.
Scientists at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) together with colleagues from the Helmholtz-Zentrum Berlin (HZB) and the University of Virginia...
13.04.2018 | Event News
12.04.2018 | Event News
09.04.2018 | Event News
26.04.2018 | Power and Electrical Engineering
26.04.2018 | Life Sciences
26.04.2018 | Power and Electrical Engineering