Nitrogen fixing by bacteria is a fascinating process that allows plants to use nitrogen from the air for their growth and development. Nitrogen is an essential element for all living organisms, as it is a component of amino acids, proteins, nucleic acids, and other biomolecules. However, most plants cannot use nitrogen in its molecular form (N2), which makes up about 78% of the atmosphere. They need nitrogen in a fixed form, such as ammonia (NH3) or nitrate (NO3-), which can be absorbed by their roots and incorporated into their metabolism.
Nitrogen fixation by bacteria is a natural phenomenon that converts N2 into fixed nitrogen compounds. There are two types of nitrogen-fixing bacteria: free-living and symbiotic. Free-living bacteria are found in the soil or water, where they fix nitrogen independently of any host organism. Some examples of free-living bacteria are Azotobacter, Beijerinckia, Clostridium, Anabaena, and Nostoc, and Paenibacillus. These bacteria can fix nitrogen under aerobic or anaerobic conditions, depending on the type of enzyme they use. The enzyme that catalyzes nitrogen fixation is called nitrogenase, which consists of two metal-containing proteins: an iron protein and a molybdenum-iron or vanadium-iron protein.
Symbiotic bacteria are those that form a mutualistic relationship with a host plant, usually a legume, such as pea, bean, soybean, clover, or alfalfa. The bacteria invade the root hairs of the plant and stimulate the formation of root nodules, which are specialized structures where the bacteria live and fix nitrogen. The most common symbiotic bacteria are Rhizobium and Bradyrhizobium, which belong to the alpha-proteobacteria group. The plant provides the bacteria with carbohydrates and other nutrients, while the bacteria provide the plant with ammonia, which is then converted into amino acids and other nitrogenous compounds by the plant.
Nitrogen fixation by bacteria is an important process for agriculture and the environment, as it reduces the need for synthetic fertilizers and enhances soil fertility and crop productivity. It also contributes to the global nitrogen cycle, which regulates the balance of nitrogen in different forms and reservoirs on Earth. Nitrogen fixation by bacteria is one of the wonders of nature that demonstrates the diversity and complexity of life on our planet.