Growth of high aflatoxin B2 mutants on defined and complex media and with ethoxyquin

The major naturally occurring aflatoxins are B1, B2, G1, and G2. A precursor-product relationship between B1 and the other toxins has been assumed by many workers, but experimental data are conflicting. Four independent reports, of mutants which produce aflatoxin B2, provide genetic evidence supporting an alternate origin for B2. Five high aflatoxin B2 mutants were obtained and grown in defined and complex liquid media and on a solid complex medium in order to determine the stability of the high B2 phenotype on different substrates and to define optimal levels of production. All the high B2 strains tested produced some aflatoxin yields were quite variable. The highest production was on complex liquid medium containing yeast extract. It was not possible to confirm reports that the antioxidant ethoxyquin was an inhibitor of G aflatoxins.