Studies on aerobic biodegradation activities of 2,4-dichlorophenoxyacetic acid by bacteria species isolated from petroleum polluted site

Bacteria species were screened and monitored for the efficiency of 2,4 - dichlorophenoxyacetic acid (2,4-D) degradation from oil degrading laboratory stock with the view to getting the most efficient 2,4-D degraders, to develop an active indigenous bacterial consortium for the bioremediation of 2, 4-D polluted systems in Nigeria. The 2,4-D was utilized as sole source of carbon attaining maximum cell densities of 10(7)cfu ml(-1) from an initial 10(5)cfu ml(-1) in 10 days. The amount of 2,4-D utilized in a batch culture by the isolates varied significantly from an initial inoculum densities of the order of 10(5)cfu ml(-1) and increased with increasing concentrations of 2,4-D. Growth rates ranged from 0.154 h(-1) to 0.180 h(-1) for SERU2 and 0.158 h(-1) to 0.183 h(-1) for SERU 11. Dioxygenase specific activity [mu g ml(-1) chloride released/mg protein)(-1) h(-1)] in actively growing cell cultures ranged from 0.010 - 0.055 (SERU 2) and 0.009- 0.045 ( SERU 11). The specific activity of the dioxygenase in the cell-free system ranged between 0.013 - 0.042 ( SERU 2) and 0.011-0.046 ( SERU 11). The pH optimum for the dioxygenase of the cell-free system was between 7.6 and 8.0 while the temperature optimum was 30 degrees C. In conclusion the results showed that the two bacteria isolates have potential for 2,4-Dichlorophenoxyacetic acid degradation and their cell-free extracts could be used as biological alternatives in the bioremediation of 2,4-D contaminated system.