Diazotroph

Diazotrophie called the growth of living beings with elemental, molecular nitrogen (N2 ) as the nitrogen source. So far Diazotrophie is known only in prokaryotic organisms. It is based on the so-called nitrogen fixation. It consists in an enzymatic reduction of N2 to ammonia (NH3).

Ecological Significance

There are both free-living (eg, Azotobacter and Clostridium ), and symbiotic nitrogen fixers ( Rhizobium, Frankia ). The often symbiotic living in and on the roots of higher plants. Set the fixed nitrogen in the form of ammonium ions (NH4 ) for protein synthesis and the synthesis of other N-containing body components available, and in return receive carbon compounds as an energy source for nitrogen fixation and growth.

The nodule bacteria of the genus Rhizobium comes to the quantitative highest importance because of their dissemination and nitrogen fixation capacity. They usually live in symbiosis with plants of the Fabaceae family ( Fabaceae, Leguminosae ). In agriculture, pea and faba bean like to be either grown for soil improvement in mixed culture with other crops, or built into the crop rotation. Alfalfa is used as green manure or as fodder.

Less well known but very important is the symbiosis of nitrogen-fixing cyanobacteria with the Algenfarn for rice cultivation, and nitrogen fixation. Actinomycetes of the genus Frankia by many shrubs and trees, such as alder and buckthorn

The ability for nitrogen fixation diazotrophic plants play a central role in the primary succession of terrestrial habitats, as the enrichment proceeds only very slowly with plant-available nitrogen by atmospheric deposition. Thus, the still occurring on moraine mountain avens in the Late Ice Age Europe was very widespread. Another typical diazotrophs pioneer plant is the green alder. A recent successional sequence on a glacial moraine with Dryas and alder can be observed in Glacier Bay National Park in the U.S. state of Alaska. The dunes tropical islands are colonized often early Casuarina.

Chemistry

The N2 - fixing process requires the use of energy in the form of adenosine triphosphate ( ATP) and a reducing agent in the form of NADPH, and specific enzymes. In rhizobia, the interplay of at least three enzyme systems is required:

The NH4 is formed by the nitrogenase used with further ATP and NADPH consumption by aminotransferases for the synthesis of amino acids.

Aspartic acid can also be used as acceptor, the end product is then asparagine.