In each experiment, one variable factor was changed, with the other variable factors remaining constant (cell mass, 2.0 107 cells/mL; BTEX mixture, 360 mg/L; NH4Cl, 0 mM; NaH2PO4, 0 mM). Periodically, BTEX concentrations of three sacrificed serum bottles were analyzed using GC as described above, and the effects of the four variable factors on BTEX degradation were evaluated by the reduction percentages of total BTEX compounds