Nitrification by aflatoxigenic strains of Aspergillus flavus and Aspergillus parasiticus.

Abstract

Summary: Four toxigenic strains each of Aspergillus flavus and A. parasiticus were grown in Schmid peptone--glucose medium to determine their ability to carry out nitrification and in a yeast extract--sucrose (YES) medium to test their toxigenicity. Two nitrifying strains each of A. flavus and A. parasiticus were grown in YES medium to examine their ability to form aflatoxin. A steam-distillation method was used to determine ammonium-, nitrite- and nitrate-nitrogen, whereas thin-layer chromatography and fluorometry served to measure aflatoxin content of broths. All eight toxigenic strains produced nitrate in Schmid and YES media when incubated without shaking. Shaking of cultures tended to increase the amount of nitrate formed in Schmid but not in YES medium. Amounts of aflatoxin produced varied with media and methods of incubation. All four nitrifying strains formed aflatoxin in YES medium. Toxigenic and nitrifying strains that gave high yields of aflatoxin did not always produce high levels of nitrate.