Effects of chlobenthiazone on aflatoxin biosynthesis in Aspergillus parasiticus and A. flavus

Isolates of Aspergillus flavus and A. parasiticus were incubated as shake and stationary submerged cultures in the presence of the fungicide chlobenthiazone. In shake culture, chlobenthiazone at 1 to 15 μg/ml had a strong inhibitory effect on the synthesis of aflatoxin B 1 (AFB 1 ) by strains of both fungi; however, inhibition of AFB 1 synthesis was always more pronounced in A. flavus than in A. parasiticus. A. flavus failed to produce aflatoxins at chlobenthiazone concentrations above 8 μg/ml; whereas, A. parasiticus continued to produce AFB 1 and other aflatoxins above this concentration. Treatment of A. parasiticus with chlobenthiazone levels above 15μg/ml often resulted in increased synthesis of AFB 1 , and the toxin levels sometimes exceeded those of the controls. In stationary cultures, chlobenthiazone also inhibited aflatoxin synthesis by both A. flavus and A. parasiticus , and a stronger inhibitory effect was again observed with A. flavus . Aflatoxin production did not increase in stationary cultures of A. parasiticus at levels of chlobenthiazone greater than 15 μg/ml, as it did in shake cultures. The differential effect of chlobenthiazone on A. flavus and A. parasiticus suggests that this compound affects an important enzymatic or regulatory site that differs in the two species.