Selection of suitable growth medium for free-living diazotrophs isolated from compost

Four free-living nitrogen fixing bacteria, namely NC 2, NC 4, NC 10 and NC 11 were tested for nitrogenase activity. NC 10 performed the highest nitrogenase activity (3.01 x 10^–3 mol/h/ml), followed by NC 4 (6.84 x 10^–4 mol/h/ml), NC 2 (2.36 x 10–5 mol/h/ml) and NC 11 (7.48 x 10^–5 mol/h/ml). The nitrogenase activity of mix culture was recorded as 7.48 x 10–5 mol/h/ml. Beijerinckia medium was the most suitable growth medium for all four organisms, followed by Derxia medium and Ashby’s medium. In these three mediums, high microbial density was obtained in a short period. The optimal growth was achieved within 48 h. Beijerinckia medium showed the highest O.D reading, 1.326 A at 24 h. This was followed by Derxia medium, 1.135 A and Ashby’s medium, 0.811 A