FIG. 4.

Number of cultivable bacteria in microcosms that received 3,000 μg g⁻¹ of xylene and high chromium at 18 μg Cr⁶⁺ g⁻¹. ▪, total number of CFU (10⁵ g⁻¹) on dilute nutrient agar. Samples were also plated on dilute nutrient agar plus 1 mM K₂CrO₄, and the viable counts on this medium are expressed as percentages of that on medium without K₂CrO₄ (•). For days 0, 4, and 7, the numbers of chromium-resistant bacteria were less than the detection limit of 3 × 10⁻³.