Although nitrogen gas composes up to 78% of Earth’s atmosphere, its triple bond makes it hard for organisms to use. To do so, microbes perform the remarkable reaction of nitrogen fixation—converting N₂ into the fertiliser and biofuel ammonia, while participating in Earth’s nitrogen cycle. The enzyme nitrogenase performs this reaction and exists in different forms depending on the metal in its metallocofactor : molybdenum, vanadium, or iron.
A study published in Nature Communications studied the nitrogenase from a deep-sea microbe living in volcanic areas, Methanocaldococcus infernus, capable of fixing N₂ at temperatures over 90 °C. The team led by Tristan Wagner (IBS/ELMA and formerly Group leader at the Max Planck Institute for Marine Microbiology, Bremen, Germany) isolated the nitrogenase directly from the microbe and found that the enzyme has astounding heat resistance : it starts to fall apart at 90 °C, and a small part of it can even survive at 98 °C. This explains why the enzyme is too slow to be active at room temperature. They used structural biology and synchrotron X-ray techniques to reveal its near-atomic structure, showing common structural features found in the three nitrogenase forms. The observation supports the proposal that the enzyme from methane-producing archaea could be similar to a common nitrogenase ancestor from which modern systems evolved. Moreover, studying how the Methanocaldococcus infernus enzyme works could reveal common mechanistic principles across all nitrogenases.
To do that, the researchers first examine the metals that compose the metallocofactor, and because of its complexity, they rely on X-ray crystallography to precisely map the identity of each metal at the atomic scale. The most challenging part was identifying molybdenum, because its signal is detectable only at a special wavelength that is usually unreachable on conventional beamlines, but accessible on the beamline BM07-FIP2 (ESRF) by pushing the experimental setup to its extreme limits. Once the molybdenum was confirmed, scientists were stunned by their next discovery : the so-called “turnover” state, only observed in the vanadium and iron nitrogenase forms, was observed for the first time in a molybdenum enzyme.
This breakthrough highlights a universal mechanistic principle among nitrogenases and marks an important milestone in understanding the nitrogen-fixation reaction, which holds great potential to tackle the climate crisis and environmental problems from eutrophication.
Molecular basis of N2 fixation in a hyperthermophilic archaeon. Maslać N, Törer MR, Bolte P, Wagner T. Nature Communications 2026 ; 17:9602.
Contact : Tristan Wagner, Extremophiles and Large Molecular Assemblies Group (IBS/ELMA) and formerly Group leader at the Max Planck Institute for Marine Microbiology, Bremen, Germany