Abstract
Free living nitrogen fixing bacteria are those that lives freely on rhizosphere of a young growing plant or those living in a close association with root of plants (Rhizobacteria) but not symbiotically. In most tropical soil, Nitrogen and other essential nutrients element are the most limiting nutrients which deficiencies could lead to slow growth and reduced crop production. Free living nitrogen fixing bacteria has the potential of secreting nitrogenase enzymes and produces organic acids such as glycolic, acetic, malic, succunic acids which fix atmospheric nitrogen directly into the soil for plants growth and development. To this end, the study on isolation, identification and screening of Azotobacter chroococcum from soil of Keffi, Nasarawa State, Nigeria was carried out from May to September 2018. Soil samples were collected from eight different locations and Azotobacter strains were isolated and identified using standard microbiological methods. The 16SrRNA gene sequence analysis of the strain showed maximum similarity of 96% with Azotobacter chroococcum of the reference type strain deposited in RDP Gen Bank database. Azotobacter strains isolated from four different locations showed coloured zone ranging between 16-10mm. Similarly, Percentage amount of nitrogen released by each Azotobacter strain in the culture broth ranging between 1.19% - 5.11% in an increasing order.
Highlights
Rhizosphere, a zone of influence around plants roots harbors alot of microoganisms
The highest nitrogen fixing activity by coloured zone formation was observed in Azotobacter species isolated from Angwan lambu (AL) with 16mm followed by pyanko with 14mm, GRA with 12mm, and the least was observed in isolate from High court (HC) with 10mm
The coloured zone formed by Azotobacter strains on nitrogen free agar plate indicates their nitrogen fixing ability and this is due to the secretion of nitrogenase enzyme
Summary
Rhizosphere, a zone of influence around plants roots harbors alot of microoganisms. Among these are the dominant rhizobacteria which prefer living close to vicinity of root plants or surface area and play a crucial role in plant growth [1]. Most tropical soil are deficient in soluble N and so is the most limiting nutrient element which deficiencies could led to slow growth and reduced crop production [3]. Nitrogen availability in agricultural soil comes either from inputs of atmospheric nitrogen by free living bacteria [4] or from biological nitrogen fixation [5]. Biological Nitrogen Fixation (BNF) is a one way process of converting elemental nitrogen from the atmosphere into plant useable form in the soil. Azotobacter and other group of rhizobacteria are actively involved in the process of BNF, Ishaya Isa Obele et al.: Isolation, Identification and Screening for Nitrogen Fixing Activities by Azotobacter chroococcum
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