Azotobacter & The Nitrogen Cycle

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Up Close and Personal As stated before, Azotobacter is a genus of bacteria that consists of gram negative rods which can range from long, thin rods to cocci shaped cells, which are found in soil and water. Cultures can often develope cysts as it ages. Azotobacter species are also nitrogen fixing bacteria that produce ammonia as an end product and do so under aerobic conditions, although some species are capbable of surviving in anaerobic conditions. Some species of Azotobacter have motility capabilities while other species do not. Azotobacter was first isolated by Martinus W. Beijerinck who also isolated Rhizobium and sulfur reducing bacteria. Azotobacter is also in the family Pseudomonadaceae.
Nitrogen Cycle Nitrification is the aerobic process of ammonium ion oxidation to nitrate and subsequent nitrite oxidation to nitrate. There are essentially four basic parts to the nitrogen cycle that includes heterotrophic nitrification, denitrification, nitrogen assimilation and nitrogen fixation. - Heterotrophic nitrification is done by bacteria and fungi in acidic environments. - The process of denitrification is a dissimilatory process in which nitrogen is used as an electron acceptor in anaerobic conditions. Major products of denitrification include nitrogen gas and nitrous oxide. - The process of nitrogen assimilation occurs when inorganic nitrogen is used as a nutrient. During this process, ammonium ions can be incorporated without high energy costs. When nitrate is assimilate, it takes large amounts of energy to reduce it.
Nitrogen Fixation - Can be carried out by aerobic or anaerobic prokaryotes. Under aerobic conditions, free living microbial genera perform this process (including Azotobacter species). - Under anaerobic conditions, nitrogen fixation is mostly done by members of the genus clostridium. - Nitrogen fixation can also occur through sybiotic relationships between bacteria and plants. - Involves a sequence of reduction steps that require large amounts of energy. Ammonia is immediately incorporated into organic matter as amine. The reductive processes occur in anaerobic conditions due to sensitivity to oxygen.