Impact of bacterial biocontrol agents on aflatoxin biosynthetic genes, aflD and aflR expression, and phenotypic aflatoxin B1 production by Aspergillus flavus under different environmental and nutritional regimes.

The objectives of this study were to examine the efficacy of four bacterial antagonists against Aspergillus flavus using 50:50 ratio of bacterial cells/conidia for the control of aflatoxin B 1 (AFB 1 ) production on two different nutritional matrices, nutrient and maize-based media at different water availabilities (0.98, 0.94 water activity (a w ) on nutrient medium; 0.995, 0.98 a w on maize meal agar medium) at 35 °C. The indicators of efficacy used were the relative expression of one structural and regulatory gene in the biosynthetic pathway ( aflD and aflR respectively) and the production of AFB 1 . These studies showed that some of the bacterial species could significantly inhibit the relative expression of the aflD and aflR genes at both 0.98 and 0.94 a w on nutrient agar. On maize-based media some of the bacterial antagonists reduced the activity of both genes at 0.94 a w and some at 0.995 a w . However, the results for AFB 1 production were not consistent with the effects on gene expression. Some bacterial species stimulated AFB 1 production on both nutrient and maize-based media regardless of a w . However, some bacterial treatments did inhibit AFB 1 production significantly when compared to the control. Overall, this study suggests that temporal studies are required on the biosynthetic genes under different environmental and nutritional conditions to evaluate the potential of antagonists to control AFB 1 . [ABSTRACT FROM AUTHOR]