Nitroreductase Enzyme Mediated Phytodegradation of 2,4,6 Trinitrotoluene by Vetiver Grass.

2,4,6-Trinitrotoluene (TNT) is the most widely used explosive and a group C human-carcinogen. We are in the process of developing a phytoremediation technique to detoxify TNT using vetiver grass. In our earlier studies we found that vetiver grass, in the presence of urea used as a chaotropic agent, was highly effective in removing TNT from both soil and aqueous media. Presence of aminodinitrotoluenes in the TNT-treated-plant tissue suggested the role of nitroreductase (NR) enzyme in the metabolic pathway of TNT. The objective of the present study was to determine the saturation kinetics of the NR enzyme from vetiver grass as function of initial TNT concentrations. Uniform biomass (50 g L^-1) of vetiver grass were allowed to grow in a plant growth chamber (at 25⁰C and 16 h photoperiod) in hydroponic media containing five initial TNT concentrations (0, 25, 50, 100, and 200 mg L^-1). Plants were harvested at different exposure times (5, 10, 15, and 30 days) to determine the kinetics of the NR enzyme. Results showed that the NR-activity (nMg^-1h^-1) was significantly (p<0.001) higher in both root and shoot tissues of the TNT-treated plants as compared to the control plants at all sampling intervals. Nitroreductase activity in the root was significantly (p<0.0001) enhanced by the increasing initial TNT concentrations, and reached its maximum level within 5 days for all TNT treatments. In contrast, while NR-activity in the shoot was significantly higher than that of the root, initial TNT treatments did not significantly influence the NR-activity. The data obtained in this experiment is highly encouraging and will be used to optimize major parameters that influence the saturation kinetics of NR in vetiver grass.