Figure 3.

Cell numbers in cultures incubated with folic acid biosynthesis inhibitors. Cultures were inoculated at day 0 to a cell number of 4 × 10⁶ cells ml⁻¹. Trimethoprim is described to inhibit dihydrofolate reductase; sulfamethoxazole (SMX) inhibits dihydropteroate reductase. All cultures contained cyanocobalamin, p-aminobenzoate, biotin and thiamine. Concentrations: Trimethoprim, 4 mg l⁻¹; sulfamethoxazole, 100 mg l⁻¹; folic acid, 20 µg l⁻¹. For each culture condition, five parallel cultures were set up and counted. Bars show the mean cell numbers and standard deviations are indicated.