Biocontrol of Aflatoxin-Producing Aspergillus flavus ATCC 22546 by a Non-Aflatoxigenic Aspergillus flavus ATCC 9643

Abstract

The biological control of Aspergillus flavus and A. parasiticus by non-aflatoxigenic strains has been introduced in cotton- and peanut-cultivating fields and proven successful at reducing aflatoxin (AFB) contamination of crops and agricultural soils. In this study, a non-aflatoxigenic strain, A. flavus ATCC 9643 (ATCC 9643), was evaluated for its ability to competitively inhibit the growth of an aflatoxigenic strain, A. flavus ATCC 22546 (ATCC 22546), and mitigate AFB production in ATCC 22546 during competitive growth. To comparatively analyze the suppressive effect of ATCC 9643 on ATCC 22546, a non-aflatoxigenic strain (A. flavus ATCC 96045, known as AF36) was used as a positive control in some experiments. The two non-aflatoxigenic strains did not produce AFB1 or AFB2 owing to the absence of several AFB biosynthesis-related genes, especially aflK and aflL, which encode versicolorin B synthase and desaturase, respectively. To create a competitive growth environment, ATCC 9643 and ATCC 22546 were co-inoculated into a solid agar medium, and they grew at similar rates when added at a 1:1 ratio. Increasing the inoculum rate of ATCC 9643 (1:1, 1:3, 1:5) dramatically inhibited ATCC 22546 growth, and AFB production was effectively decreased by about 84%, 95%, and 97% by treatment with ATCC 9643. On rice, ATCC 22546 attenuated ATCC 9643 growth only when the rice was submerged in distilled water, whereas agar addition enhanced it. Taken together, ATCC 9643 is a promising candidate biological agent for suppressing aflatoxigenic A. flavus strain growth and alleviating AFB contamination. Further studies on AFB reduction in crop fields, including cotton-cultivation and maize-cultivation fields, are warranted.