Isolation and characterisation of non symbiotic nitrogen fixing bacteria (Azotobacter sp.) from tea field soil of terai region of North Bengal, India

Total 126 distinct colony has been isolated, 31 colony from TS-1, 30 colony from TS-2, 25 colony from TS-3 and 40 colony from TS-4 from different location Terai Tea garden. Most of the colonies are 1.0–4.5 mm in diameter in size, circular even with rarely undulated colonies(shape), white or creamy translucent with central black dot. The selected 23 purified colonies so far tested for salinity test, TS-1-13, 19, 26, 27; TS-3-10, 24; TS-4-16 showed highest salinity tolerance upto 4.5% and TS-1-13, 26, TS-3-24, TS-4-16 showed highest salinity tolerance upto5.0%. Among 19 pure isolates from the Terai soil sample (TS-1-TS-4), maximum isolates (TS-1-1, 18, 19 TS-2-14, 15, 16, TS-3-27, 28, 33 and TS-4-32) exhibited highest resistance against Rifampicin (35mg/l). Among 19 pure isolates from the Terai soil sample TS-2-14, TS-3-27, TS-4-32 showed highest level(30mg/l of resistance against chloramphenicol. Among 19 isolated pure culture so far tested against tetracyclin TS-1-13, 19, TS-2-7, TS-3-33 showed highest level (25mg/l) of resistance. Isolates number TS-1-3, 19, TS-2-7, 14, 28 showed medium level of resistance at 30mg/l against tetracyclin. Among six selected isolated strains of Azotobacter, the strain no. TS-1--13, TS-1-26, TS-3-3 and TS-4-16 showed maximum level (0.006%) of nitrogen uptake capacity, which indicates that these strains would be used as biofertiliser in Tea field subject to their validation in field study.