Laboratory experiments were performed to characterize and identify 2,4-dinitrotoluene (DNT)-degrading bacterial strains isolated from crude oil contaminated soil from a landfill dump site of a petroleum refinery in Mersin, Turkey. Fluorescent in situ hybridization (FISH) with dntAa probes encoding 2,4-DNT dioxygenase was used to detect 2,4-DNT-degrading bacteria. The direct FISH analysis of soil samples collected from a petroleum refinery showed very weak signals. Therefore, a selective enrichment culture technique using 2,4-DNT as the sole carbon source was then used to isolate DNT degrading bacteria. Following the culture enrichment procedure, the hybridization signals improved significantly in the isolated bacterial strains. Based on 16S rRNA sequences, the bacteria isolated from the soil samples were identified as Arthrobacter sp. Results from the batch biodegradation experiments indicate that the biodegradation rates of 2,4-DNT with this strain were highly dependent on environmental conditions such as pH and temperature, with optimum conditions obtained at 30 A degrees C and pH similar to 7. A first-order kinetic model was able to accurately describe 2,4-DNT degradation rates under different environmental conditions (e.g., pH). The ability of Arthrobacter sp. for degrading 2,4-DNT was found to be plasmid-mediated through curing experiments. The size of the plasmid involved, referred to as pArK1, was estimated to be about 8.1 kb.