Submitted to: International Society on Toxicology Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 11/30/2003
Publication Date: N/A
Technical Abstract: Aflatoxins (AF), among the most potent carcinogens known, are produced by some, but not all, strains of Aspergillus flavus and A. parasiticus. In most countries AF is the most important mycotoxin contaminant of corn, cottonseed, peanuts, tree nuts, copra and other agricultural products. Heat stress is widely accepted to favor AF production; conditions favoring fumonisin production have not been so well defined. Studies undertaken to better define the conditions which favor AF and fumonisin contamination of corn in Mississippi and Arkansas indicated (i) the most important factor favoring AF contamination was high (>20 deg C) night temperatures; (ii) corn hybrids selected for AF resistance yielded crops with dramatically lower AF and significantly less fumonisin contamination; and (iii) fumonisin contamination was favored by hot humid conditions and occurred simultaneously with and independent of AF contamination. Several studies have observed a higher % toxigenic strains in the soil reservoir of A. flavus than in naturally-infected crop plants, suggesting that toxigenicity is not a virulence factor. These observations lend support to strategies for reducing AF contamination by preinoculation with non-toxigenic strains. These strategies need a bank of non-toxigenic strains that can be screened for ability to produce stable, infectious spores that compete effectively with toxigenic strains under field conditions. Saito and Machida (Mycoscience, 40, 205, 1999) developed a rapid method for identifying AF-producing and non-producing strains of A. flavus and A. parasiticus, which may provide a useful pre-screen for identifying non-toxigenic strains. In this method, the reverse side of AF-producing colonies turn from yellow to pink immediately after exposure to ammonium hydroxide vapor. The yellow pigments have been isolated and shown to be pH indicator dyes, which turn from yellow to pink at pH > or = to 8 by addition of any base, and turn yellow again when the pH is lowered with acid. Seven pigments representing most of the color, were identified by comparing spectroscopic and chromatographic properties with literature or predicated values. These pigments are or have been related to the pigmented intermediates in the AF pathway: versicolorin C, versicolorin A hemiacetal, nidurufin, averufin, versicolorin A, norsolorinic acid, and averantin. Identification of the pigments that predict AF production by A. flavus strains as being AF biosynthetic intermediates provides a convenient rationalization for the predictive power of the method.