Polyene-resistant mutants of Aspergillus fennelliae: identification of sterols.

Four mutants strains of Aspergillus fennelliae resistant to various polyene antibiotics have been analyzed for their sterol content. The mutant strains contained Delta(7,22,24(28))-ergostatrien-3beta-o1 and Delta(7,22)-ergostadien-3beta-o1 as the major sterols, whereas the wild types contained ergosterol, indicating that the mutants contain metabolic blocks for C(5)-C(6) dehydrogenation and C(24)-C(28) reduction in the biosynthesis of ergosterol. Revertant sectors arising from the mutant colonies contained either more Delta(7,22)-ergostadien-3beta-o1 than the parent mutant strain or showed the reappearance of ergosterol. The revertant sectors also showed lower resistance to amphotericin B and a higher rate of sporulation than the parent mutant strain. These results confirm our previous observations that the presence of ergosterol is directly related to the drug susceptibility and the normal rate of sporulation in this species.