Sterol content and enzyme defects of nystatin-resistant mutants of Neurospora crassa

Abstract

Non-saponifiable cell extracts of wild type and sterol mutants of N. crassa were analysed by means of gas-liquid chromatography. The wild-type contained ergosterol and episertol in a 10:1 ratio. None of the mutants was able to synthesize ergosterol. Three of the mutants carry single recessive gene mutations cauisng blocks in the terminal steps of ergosterol biosynthesis: erg-1 has an inactive delta 8 leads to delta 7 isomerase erg-2 has an inactive 24(28) hydrogenase, and erg-4 has an inactive C-24 methyl transferase. Some of the mutants accumulated novel sterols as a result of their enzyme defects. The genes erg-1 and erg-2 were mapped close to inl on the right arm of chromosome V.

Identification of a sterol mutant of Neurospora crassa deficient in A14,15-reductase activity

“…Ultraviolet spectrophotometry of sterol extracts from the mutant erg-3 showed an absorption maximum at 250 nm and a shoulder at 245 nm, which confirmed the observations of Grindle & Farrow (1978). Such a spectrum is characteristic of A8v1 4-sterols (Mercer, 1988).…”

“…Mutants of filamentous fungi blocked at similar steps in the sterol biosynthesis pathway have also been isolated. For example, Grindle & Farrow (1978) reported mutants of Neurospora crassa with gene defects affecting isomerization (erg-1), 24(28) hydrogenation (erg-2) and C-24 transmethylation (erg-#).…”

Phenotypic Differences Between Natural and Induced Variants of Botrytis cinerea

“…Nystatin kills normal strains of N. crassa by binding to the ergosterol component of cell membranes so that the membrane is distorted and cell contents leak out. Resistant mutants carry recessive gene mutations causing blocks in ergosterol biosynthesis (Grindle & Farrow, 1978). Cell extracts of B. cinerea cultures, analysed as described by Grindle (1973), were found to contain ergosterol : it seems unlikely, therefore, that nystatin-resistant mutants have not been recovered because B. cinerea lacks appropriate mutable genes.…”

Protoplast Fusion Hybrids of Candida albicans Sterol Mutants Differing in Nystatin Resistance

“…A number of genetic studies concerning the polyene antibiotic resistance of Saccharomyces cerevisiae and Neurospora crassa have been published, demonstrating that resistance to nystatin is due to both dominant and recessive gene mutations (Pate1 & Johnston, 1968;Ahmed & Woods, 1972;Molzahn & Woods, 1972;Bard, 1972;Karunakaran & Johnston, 1977;Grindle & Farrow, 1978).…”