Impact of Mg2+, Fe2+ and Co2+ Metal Ions on Growth and Ochratoxin A Production by Strains of Aspergillus westerdijkiae and Aspergillus carbonarius

The efficacy of metal ions (150, 500, 1000 mu M; Mg2+, Fe2+ and Co2+) on growth of 2 strains each of Aspergillus westerdijkiae and Aspergillus carbonarius and chratoxin A (OTA) production was studied on a conducive yeast extract sucrose agar medium (YES) at different water activity levels (a(w), 0.92, 0.97). A(w) was the main factor affecting growth of the tested strains. In general, the growth of strains of A. carbonarius was faster than those of A. westerdijkiae. At 0.97 a(w) the metal ion Co2+ inhibited growth of the tested strains, with the exception of a type strain of A. westerdijkiae. Addition of the metal ions had contrasting results on OTA production. Addition of metal ions was the main factor affecting OTA production. Mg2+, notably at 1000 mu M, promoted OTA production by the tested strains at both aw levels. The metal ions Fe2+ and Co2+ had either no effect or inhibited OTA production at both aw levels with exception of Co2+ at 1000 mu M which significantly increased OTA production by the type strains of A. westerdijkiae at 0.92a(w).