Response of Ammonia-Oxidizing Bacteria and Nitrite-Oxidizing Bacteria to Cadmium at an Elevated Concentration

The study was undertaken to investigate the effect of cadmium on different nitrifying bacteria. The response of heavy metal salt on Ammonia-oxidizing bacteria(AOB) and Nitrite-oxidizing bacteria(NOB)isolated from soil samples were investigated by supplementing cadmium (Cd)at four loading rates(100, 200, 500, 1000 µg/ml) in mineral salt broth with Ammonia Oxidizing Bacteria (AOB) and Nitrite-oxidizing bacteria(NOB)isolates. The cultures were incubated for 7 days. Growth of AOB and NOB were measured by withdrawing samples from the medium every 24 hours and absorbance of the turbidity measured at 600 nanometre using spectrophotometer. All bacteria showed high tendency to decrease optical density while increasing metal concentration in the medium. Tolerance for the metal ions was dependent on concentration, time and the isolate tested. Analysis of variance shows that there is a significant difference (P < 0.05) in the nitrifying bacteria response rates to heavy metal salts (Cadmium (Cd)) at four loading rates (100, 200, 500, 1000 µg/ml)) between the treated and the untreated. All the Ammonia oxidizing bacterial (AOB) and Nitrite-oxidizing bacteria (NOB)showed a high level of sensitivity for the metals tested, and exhibited low growth at all metal salt concentrations tested.