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Nitrogen fixation
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<p>Nitrogen fixation is a <a href="/facts/Chemical_process/EBSGtK3y">chemical process</a> by which molecular <a href="/facts/Dinitrogen/Nf1QpGDz">dinitrogen</a> (N2) is converted into <a href="/facts/Ammonia/MtLtJFtz">ammonia</a> (NH3). It occurs both biologically and <a href="/facts/Abiological_nitrogen_fixation/m8q36uBL">abiologically</a> in <a href="/facts/Chemical_industry/3M6gfHer">chemical industries</a>. Biological nitrogen fixation or <i>diazotrophy</i> is <a href="/facts/Catalyze/LPBS7TQC">catalyzed</a> by <a href="/facts/Enzyme/DSI1Fh7y">enzymes</a> called <a href="/facts/Nitrogenase/gIhxgCaL">nitrogenases</a>. These enzyme complexes are encoded by the <a href="/facts/Nif_gene/s6pIrE7A"><i>Nif</i> genes</a> (or <i>Nif</i> <a href="/facts/Homolog/muctKlyT">homologs</a>) and contain <a href="/facts/Iron/QK1JYy8E">iron</a>, often with a second metal (usually <a href="/facts/Molybdenum/RX6vp2bF">molybdenum</a>, but sometimes <a href="/facts/Vanadium/UvKkKTSm">vanadium</a>). </p><p>Some nitrogen-fixing bacteria have <a href="/facts/Symbiotic/MrBArRGa">symbiotic</a> relationships with <a href="/facts/Plant/X5BMDMvS">plants</a>, especially <a href="/facts/Legume/x6s6gVHY">legumes</a>, <a href="/facts/Moss/YF8Rbf8y">mosses</a> and <a href="/facts/Aquatic_fern/nk7CXCam">aquatic ferns</a> such as <i><a href="/facts/Azolla/2pgFpADh">Azolla</a></i>. Looser non-symbiotic relationships between diazotrophs and plants are often referred to as associative, as seen in nitrogen fixation on <a href="/facts/Rice/wvL1hBCz">rice</a> roots. Nitrogen fixation occurs between some <a href="/facts/Termite/KRFbDumW">termites</a> and <a href="/facts/Fungus/BHo5DP59">fungi</a>. It occurs naturally in the air by means of <a href="/facts/NOx/aC4Squ7z">NOx</a> production by <a href="/facts/Lightning/dLTuxz8n">lightning</a>. </p><p>Fixed nitrogen is essential to <a href="/facts/Life/DNw7NUId">life</a> on <a href="/facts/Earth/HLLmDfj0">Earth</a>. All nitrogen-containing <a href="/facts/Organic_compounds/gqCNaN45">organic compounds</a> such as <a href="/facts/DNA/nB89Iauz">DNA</a> and <a href="/facts/Protein/Jxmagu3E">proteins</a> contain nitrogen. Industrial nitrogen fixation underpins the manufacture of all nitrogenous <a href="/facts/Industrial_product/v5CPEj8p">industrial products</a>, which include <a href="/facts/Fertilizer/ysh3r6NJ">fertilizers</a>, <a href="/facts/Pharmaceutical/h9mhwWP2">pharmaceuticals</a>, <a href="/facts/Textile/PJrVeM5S">textiles</a>, <a href="/facts/Dye/a1NSlcsG">dyes</a> and <a href="/facts/Explosive/sUme5Pp8">explosives</a>. </p>