After incubation, the cell density was measured at 600 nm (OD600), and the culture broth was extracted twice with 10 ml of n-hexane each time. All extracts were evaporated to a final volume of 2 ml with a nitrogen stream. Hydrocarbons were quantified by gas chromatographic (GC) system (Varian 3380, Palo Alto, USA) equipped with an SPB-5 column (0.32-mm i.d. 30-m length, Supelco). The total area of detected hydrocarbon peaks was defined as the concentration of TPHs. Percentage of degradation was calculated by the following expression: Percentage of degradation = [(TPHs control TPHs treatment)/ TPHs control] 100. The sterile controls were inoculated with heat-killed cells autoclaved at 115 C for 10 min. Each test flask was prepared in triplicate. The correlation of growth and degradation was analyzed with Statistical Product and Service Solutions 13.0 (SPSS 13.0) software package.