Each culture flask was inoculated with 1mL of bacterial suspensions containing 103–104 cells mL1. The bacterial inoculum was prepared from 24 h nutrient or malt broth cultures,incubated at 180 rpm and 28 1C. The bacterial suspension (in distilled water) was counted by decimal dilution on spread plates. After three cycles of enrichment, the hydrocarbon-degrading
bacteria were purified using the basal mineral salts medium in which diesel oil was the sole carbon and energy source. Isolates were then maintained on tryptic soy agar.