After years of research, the molecular structure of the enzyme that is responsible for a large part of the worldwide nitrate and nitrogen production by bacteria is known. The anammox bacteria, among others, use this enzyme to convert toxic nitrite into nitrate. Now that it has been clarified exactly how this enzyme works, this creates new possibilities for making better use of the anammox bacteria for power generation from wastewater and the production of rocket fuel. Researchers from Radboud University and the Max Planck Institutes in Heidelberg and Frankfurt are publishing about it today in Nature Microbiology .
Nitrogen-eating bacteria such as anammox require the enzyme nitrite oxidoreductase (NXR) to convert the toxic nitrite to nitrate. The enzyme plays a central role in the nitrogen cycle in nature. For example, through fertilizer use in agriculture, a lot of ammonium ends up in the soil, which is then converted to nitrate. Nitrate is easily soluble in water, which means that it is easily washed away in ground and surface water. That process is an important reason why too much nitrogen has such a big environmental impact.
‘Despite the fact that the enzyme is so important for the nitrogen cycle, we knew very little about how it works,’ says Mike Jetten , professor of Microbial Ecology at Radboud University. ‘It took us more than ten years to map out the molecular structure of this enzyme in the anammox bacterium.’
‘NXR turns out to be complicated and to contain unexpected parts,’ says Thomas Barends of the Max Planck Institute for Medical Research in Heidelberg. ‘Together with our colleagues in Frankfurt, we have found a building block in it that ensures that the protein joins together into long threads. We have now also gained more insight into how proteins can organize themselves in the cell in general.’
Wastewater and rocket fuel
The fact that it is now finally known how NXR works helps, among other things, in using the anammox bacterium for interesting applications. Jetten: ‘Anammox needs this enzyme to grow, but naturally grows very slowly. Now we may be able to remove the bottlenecks in the growth process, so that we can use the bacterium in smaller and faster installations.’
Nijmegen microbiologists have been studying the properties of the special anammox bacterium for a long time. This is because it is the only one in the world capable of converting harmful ammonium into harmless nitrogen gas without using oxygen. Since the discovery of the bacterium, anammox has been widely used for wastewater treatment.
A year ago, the microbiologists discovered that the bacteria can help generate electricity from wastewater. ‘We made this – initially impossible – reaction possible by bypassing the NXR enzyme. It is also still on our bucket list to have anammox produce rocket fuel on a large scale. It is also useful for this if we know how we can better circumvent the enzyme: then the bacterium will focus less on growth, but more on making the by-product hydrazine, a raw material for rocket fuel. ‘
‘Architecture of the Intracellular Superstructure-Forming Nitrite Oxidoreductase’, Tadeo Moreno Chicano et al., Nature Microbiology . DOI: 10.1038/s41564-021-00934-8
Provided by Radboud University