Biological Traits of Azotobacter Isolated from Marginal Soils and their Resistance to Tetracycline

Multiple stress in soil due to abiotic and biotic stressor are the constraints of plant production. Human activity contributes to soil abiotic stress such as salt and heavy metal accumulation, and biotic stress cause by soil tetracycline contamination from manure. Nitrogen-fixing Azotobacter enable to increase plant growth and perform the biological activities in stressed soil. The objective of laboratory experiment was to determine the plant growth-related properties of some strain of Azotobacter isolated from saline and mercury-contaminated soil. Five isolates of Azotobacter were grown in liquid medium prior to nitrate, phytohormones, organic acids, and phosphatase analysis. All isolates were then tested for their susceptibility of tetracycline. Based on antibiotic resistance test, two Azotobacter isolates were further assessed for their ability to proliferate and produce exopolysaccharide in tetracycline-contaminated broth. The results verified that the five Azotobacter isolates produced different amounts of important metabolites for plant growth. Azotobacter c2a9 and K4 isolated from mercury- and salt-contaminated soil can respectively proliferate in the liquid culture with 5 mg/L-87.5 mg/L tetracycline. In the presence of 100 mg/L tetracycline, their growth was limited but they still produced low concentration of exopolysaccharides. This experiment suggested that Azotobacter has a potency to improve plant growth in the multiple-stressed soil.