Nitrogen-fixing Bacteria and their Applications in the Environment: A Review
Authors: Alomari Sawsan M , Hasan Rana S , Najim Alaa Nazar Al- , Saadi Ali M 
Published: December 2024

The process of converting nitrogen into ammonia in the form of a compound is referred to as biological nitrogen fixation. This process is accomplished by various types of nitrogen-fixing bacteria. In this process, atmospheric dinitrogen is enzymatically converted into ammonia by nitrogen-fixing microorganisms. These nitrogen-fixing bacteria are broadly classified into two groups: symbiotic nitrogen-fixing bacteria and non-symbiotic nitrogen-fixing bacteria. Within the microbial cells, ammonia is used for the maintenance and development of the bacterial cells. These microorganisms produce several enzymes, proteins, and cofactors that are essential for the functioning of the key enzyme nitrogenase. This enzyme is capable of reducing inert nitrogen molecules to ammonia. The entire process involves the electron transport chain within the bacterial cell. Two of the many diverse genera of rhizobia, Rhizobium and Bradyrhizobium, are α-proteobacterial diazottrophic families that form root nodules through the interaction of symbiotic genes. The nitrogen-fixing symbionts of actinophytes are symbiotic rhizobia of the genera Mesorhizobium, Sinorhizobium and Bradyrhizobium, such as Azorhizobium. The genera Frankia and Discorrhizobium provide drought-resistant forage roots in non-legume actinophytes such as alder and myrica woodlands. Frankia actinophytes have the ability to live as sugar and cellulose decomposers in addition to being symbiotic with actinophytes. Integrating nitrogen-fixing bacteria into integrated disease management can lead to significant plant growth. Research involving the application of biofertilizers in a variety of crops is at an interactive level. Nitrogen-fixing bacteria can fix nitrogen from the air into the root zone under both free and bonded nitrogen fixation. In some cases, co-inoculation of mycorrhizal spores together with nitrogen-fixing microorganisms and Azospirillum strains has shown improvement in plant health. Nitrogen-fixing bacteria can improve the structure and fertility of soils that have been degraded for various reasons. Therefore, nitrogen-fixing bacteria have the potential to be used in environmental remediation processes to treat wastewater, human and animal waste, or overcome other disinfection caused by industrial pollutants. In environmental nitrogen cycles, the application of nitrogen-fixing bacteria can provide opportunities for the accumulation and preservation of organic matter through different particle sizes. However, it is necessary to identify nitrogen-fixing bacteria endemic to different ecosystems and study the potential biochemical cycles of nitrogen in different sized mineral components. In addition, the efficiency rates of chemical remediation should be compared due to potential problems with the development of concentrations of these microorganisms in environmental restoration or bioremediation processes over large areas. There is hope for the positive development of strategies to eliminate harmful metals in soil and restore potential management profits under the green economy policy, with the preferential use of extreme organisms living within soil elements, which will contribute to different strategies for the use of nitrogen fertilizers in agriculture.