Pesticide tolerant Azotobacter isolates from paddy growing areas of northern Karnataka, India

A total of 14 Azotobacter strains were isolated from different paddy cultivating soils with pH ranging from 6.5 to 9.5 by using serial dilution agar plate method. The strains were Gram negative, rod shaped, cyst forming and developed brown to black colored colonies, which were glistening, smooth, slimy on Ashby's agar plates. Biochemically they were positive for biochemical tests namely, indole production, citrate, catalase, carbohydrate fermentation and Voges-Proskauer test. Further, sequence analysis of PCR amplicons obtained from these cultures revealed the presence of five different Azotobacter species viz., Azotobacter vinelandii, Azotobacter salinestris, Azotobacter sp., Azotobacter nigricans subsp. nigricans and Azotobacter tropicalis. Phylogenetically these strains were grouped into two distinct clusters. These strains were tested for their ability to grow on a media containing four different pesticides such as pendimethalin, glyphosate, chloropyrifos and phorate, which are commonly used for the paddy. Out of 14 strains tested, 13 strains were able to grow on a media containing herbicides such as pendimethalin, glyphosate and insecticides like chloropyrifos and phorate. However, five Azotobacter strains were able to grow at higher concentration of 5 % pesticides, without affecting their growth rate. Further, the effect of pesticides on the indole acetic acid (IAA) production by Azotobacter strains was also estimated. Azotobacter-16 strain was found to produce 34.4 mu g ml(-l) of IAA in a media supplemented with 1,000 mg of tryptophan and 5 % of pendimethalin. Present study reveals that species of Azotobacter are able to grow and survive in the presence of pesticides and no significant effects were observed on the metabolic activities of Azotobacter species.