| Summary: | Aflatoxin B1 is one of the most deleterious types of mycotoxins. The application of an endophytic fungus for biodegradation or biosuppression of AFB1 production by <i>Aspergillus flavus</i> was investigated. About 10 endophytic fungal species, isolated from healthy maize plants, were screened for their in vitro AFs-degrading activity using coumarin medium. The highest degradation potential was recorded for <i>Trichoderma</i> sp. (76.8%). This endophyte was identified using the rDNA-ITS sequence as <i>Trichoderma harzianum</i> AYM3 and assigned an accession no. of ON203053. It caused a 65% inhibition in the growth of <i>A. flavus</i> AYM2 in vitro. HPLC analysis revealed that <i>T. harzianum</i> AYM3 had a biodegradation potential against AFB1. Co-culturing of <i>T. harazianum</i> AYM3 and <i>A. flavus</i> AYM2 on maize grains led to a significant suppression (67%) in AFB1 production. GC-MS analysis identified two AFB1-suppressing compounds, acetic acid and n-propyl acetate. Investigating effect on the transcriptional expression of five AFB1 biosynthesis-related genes in <i>A. flavus</i> AYM2 revealed the downregulating effects of <i>T. harzianum</i> AYM3 metabolites on expression of <i>aflP</i> and <i>aflS</i> genes. Using HepaRG cell line, the cytotoxicity assay indicated that <i>T. harazianum</i> AYM3 metabolites were safe. Based on these results, it can be concluded that <i>T. harzianum</i> AYM3 may be used to suppress AFB1 production in maize grains.
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