FIGURE 4.
A. nidulans mutants in the peroxisomal β-oxidation cycle require biotin for growth. Spores (103) from a control (CTL) biotin-prototrophic strain (FGSC A1145) and from biA1, ΔbioF, ΔaoxA, ΔaoxB, ΔpexE, and ΔfoxA mutants were point-inoculated individually in wells of a 24-well microtiter plate containing either minimal medium supplemented with biotin (lower row) or biotin-deficient minimal medium supplemented with avidin (upper row) or with avidin and pimelic acid (middle row) and incubated for 1 day at 37 °C and for 2 days at 28 °C. As reported previously (26), the ΔpexE mutant showed reduced sporulation compared with all other strains, even when grown on medium containing biotin, explaining the paler appearance of the ΔpexE colony. However, the mycelial growth rate of the ΔpexE mutant (colony diameter and mycelial density) is comparable with that of the wild-type control strain on biotin-supplemented medium.