Nitrogen fixation 'off switch' discovery could one day help crops make their own fertilizer
Nitrogen is essential for life. It's needed to build proteins, DNA and many other components of cells. Although nitrogen gas makes up almost 80% of Earth's atmosphere, most organisms cannot use it directly. Certain microbes solve this problem through a process called nitrogen fixation, which converts nitrogen gas into ammonia. This process is carried out by an enzyme called nitrogenase.
Nitrogen, vital for life, is necessary to construct proteins, DNA, and numerous cellular components. Despite nitrogen gas comprising around 80% of Earth's atmosphere, most organisms cannot directly utilize it. Certain microbes overcome this hurdle via a process termed nitrogen fixation, where the atmospheric nitrogen gas is converted into ammonia.
This process is facilitated by an enzyme known as nitrogenase. Gaining insights into this enzyme's functionality could pave the way for more efficient, naturally based ammonia production, a key ingredient in widely used fertilizers.
A research collaboration from the U.S., led by the University of Arkansas, focused on nitrogenase and its regulation within a methane-producing microbe called a methanogen. Utilizing high-resolution cryo-electron microscopy, they uncovered that methanogen nitrogenase can bind with regulatory proteins to form a large inactive compound, termed a protein supercomplex.
This newly identified supercomplex operates as a molecular off switch, halting nitrogen fixation when the cell's energy or nutrient levels are insufficient. Cellular signals indicating energy and nutrient levels can disassemble this complex, reactivating enzyme activity and resuming nitrogen fixation.
Dan Lessner, a professor of biological sciences at the University of Arkansas and the study's corresponding author, emphasized the significance of this discovery. Nitrogen fixation is vital for agriculture, food production, and ecosystems globally. Furthermore, it enhances our understanding of microbial physiology, the global nitrogen cycle, and the evolution of nitrogen fixation, while offering potential insights for future biotechnology and sustainable agriculture applications.
The primary limitation to plant growth often stems from an inadequate nitrogen supply, even when plants receive sufficient sunlight, water, and CO2, according to Lessner. When plants lack sufficient nitrogen, their growth remains stunted, especially in terms of producing plant material for human and animal consumption. The conventional method of fertilizer production chemically transforms nitrogen from the atmosphere into ammonia in high-pressure reactors powered by fossil fuels.
The resultant nitrogen-based fertilizer is then applied to fields, hoping the plants will uptake it. This process often results in excessive fertilizer runoff into streams and waterways, causing algal blooms, habitat degradation, and biodiversity loss.
The nitrogenase enzyme can perform the atmospheric nitrogen-to-ammonia conversion biologically under standard temperature and pressure conditions. Understanding how this enzyme functions could potentially enable its use as a catalyst in an energy-efficient and environmentally friendly method to produce ammonia for fertilizer. Through genetic studies, the researchers could potentially transfer this genetic information into plants, such as corn, allowing plants to potentially fix their own nitrogen from the atmosphere and eliminate the need for fertilizer. This development would have profound economic, social, and environmental implications.
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