Scientists at the Max Planck Institute for Marine Microbiology studied nitrogen fixation in Methanocaldococcus infernus, a deep-sea archaeon that thrives in volcanic marine environments where temperatures exceed the boiling point of water. The organism accomplishes this feat through an enzyme called nitrogenase, which breaks the exceptionally strong triple bond in atmospheric nitrogen gas and converts it into ammonia that living organisms can utilize.
The research team successfully cultivated the microorganism in laboratory conditions and isolated its nitrogenase enzyme, discovering it possessed remarkable thermal stability compared to most proteins. The enzyme remained partially intact at temperatures as high as 98°C, while continuing to function only at elevated temperatures rather than at room temperature. This heat resistance enabled researchers to study molecular states of the enzyme that are typically difficult to observe under normal conditions.
Using advanced structural biology techniques at a synchrotron facility in France, the team determined the enzyme’s molecular structure at near-atomic resolution. The analysis revealed that this archaeal nitrogenase represents the simplest known form of the enzyme while simultaneously incorporating structural characteristics from all three major nitrogenase families: those based on molybdenum, vanadium, and iron. This combination suggests that ancient nitrogenases may have more closely resembled this deep-sea enzyme than modern bacterial versions.
During their investigation, researchers identified an unexpected molecular state within the molybdenum-containing enzyme that had previously been observed only in vanadium and iron-based nitrogenases. This discovery indicates that all nitrogenase forms may employ a common underlying mechanism for breaking apart nitrogen molecules. The findings have potential implications for biotechnology applications and agriculture, including the possibility of reducing fertilizer production through industrial processes that generate significant greenhouse gas emissions.
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