Isolation and Characterize of Nitrogen-Fixing Bacteria Bacillus spp. and their Response to some Environmental Variables

The study included two axes: the first was isolation and diagnosis of Bacillus spp. that fixed atmospheric nitrogen from 10 different soil samples collected from the city of Mosul, diagnosed microscopically and culturally depending on several biochemical tests.Its effectiveness in fixing nitrogen was tested by inoculating it in a nitrogen-free medium with the presence of a control sample.The best isolate (F5) was chosen to conduct the second section, which aimed to determine the effect of environmental factors, such as different temperatures, the effect of high salt content and different pH ranges on the ability of Bacillus to produce nitrogenase, which is important in fixing nitrogen.The results showed that the optimal growth of the isolate (F5) was on Nutrient Agar at a temperature of 37°C and a pH of 7. The bacteria were grown at temperatures of 40°C, 45°C, and 50°C, the isolate (F5) tolerated growth to a temperature of 50°C, as there was a significant difference compared to control sample, in addition to retaining its ability to fix nitrogen.The bacteria were grown in culture media containing 6%, 7%, and 8% concentrations of NaCl, and they tolerated growth to a concentration of 8%, with a slight significant difference to the control sample.The bacteria retained their ability to fix nitrogen at 6%, 7%, and at a concentration of 8%, there was a slightly significant difference compared to the control sample.It was also grown on media with pH value of 6, 5 and 4.There was a slight significant difference in the level of pH 6 when compared to the control sample, while at the level of pH 5 there was weak growth with a large significant difference compared to the control sample, and no bacterial growth appeared at pH 4. Nitrogen was fixed at pH6 and there was no significant difference compared to the control sample.However, a very small amount of nitrogen was fixed at pH5 and it was with a large significant difference compared to the control sample.