POSSIBLE ROLE OF ERGOSTEROL OXIDATION IN AFLATOXIN PRODUCTION BY ASPERGILLUS-PARASITICUS

The di-unsaturated linoleic acid and the tri-unsaturated ergosterol (ERG) represent the main poly-unsaturated molecules in membranes of Aspergillus parasiticus. The addition to Czapek Dox broth medium (CDM) cultures of A. parasiticus of compounds such as carbon tetrachloride (CCl4) or cumene hydroperoxide (CUH), which are capable of inducing cell lipoperoxidation, causes a rapid and significant fall of microsomal and mitochondrial ERG concentrations (ng mg(-1) D.w.), but not of linoleic acid. A discharge of aflatoxins (AFT) follows ERG level reduction and it is associated either with a renewal of fungal growth due to nutrients (deriving from cell lysis and CCl4 or CUH catabolism), or with a slow increase of ERG in microsomes and mitochondria, which, in any case, does not reach the levels of the sterol present in these subcellular fractions before supplementations. A slight decrease of microsomal and mitochondrial ERG occurs also when substrates metabolizable by the fungus (yeast extracts, sucrose, 1-aminoacids) are added to CDM cultures. We suggest that ERG fall, probably due to oxidation, may be considered a trigger able to induce either further fungal growth or secondary metabolism stimulation.