A heat-stable enzyme from the deep-sea archaeon Methanocaldococcus infernus has been discovered to convert nitrogen gas (N₂) into ammonia, a critical process known as nitrogen fixation. This microorganism lives in extreme environments, such as marine volcanic areas where temperatures can surpass the boiling point of water. Scientists from Tristan Wagner's lab at the Max Planck Institute for Marine Microbiology in Bremen have been studying this organism, successfully isolating a nitrogenase enzyme that remains stable even at very high temperatures, with some samples surviving at 98°C (208°F). The nitrogenase enzyme contains a metallocofactor, a type of metallic molecule that helps the enzyme perform its function. While most well-studied nitrogenases use a metallocofactor with molybdenum, others use vanadium or iron instead. The nitrogenase from Methanocaldococcus infernus appears to have characteristics of all three types, suggesting it might represent an ancient form of nitrogenase. This could offer insights into the fundamental mechanisms behind nitrogen fixation across different organisms. The study, published in Nature Communications, used advanced techniques such as microbial physiology, enzyme purification, biochemistry, and structural biology. These experiments were conducted under strictly oxygen-free conditions to protect the enzyme's delicate metallocofactors. Researchers crystallized the enzyme and studied its structure at the Institut de Biologie Structurale in Grenoble, France, using a synchrotron to generate high-intensity X-rays. This allowed them to achieve a near-atomic-resolution view of the enzyme, revealing it to be the simplest known nitrogenase, combining features from all three known nitrogenase families. The team also identified a previously unknown state in a molybdenum-containing nitrogenase, suggesting that all nitrogenases may follow a similar mechanism when breaking down nitrogen gas. This discovery could have important applications in biotechnology. Methanocaldococcus infernus and similar microorganisms not only help convert nitrogen into ammonia but also play a key role in Earth's carbon cycle by producing a significant portion of atmospheric methane. In the future, these organisms might be used as biological tools for converting gases into valuable products like methane and ammonia, potentially using green hydrogen as a renewable energy source.