Biodegradation of Aflatoxin B1 in Maize Grains and Suppression of Its Biosynthesis-Related Genes Using Endophytic Trichoderma harzianum AYM3.

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 Aspergillus flavus 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 Trichoderma sp. (76.8%). This endophyte was identified using the rDNA-ITS sequence as Trichoderma harzianum AYM3 and assigned an accession no. of ON203053. It caused a 65% inhibition in the growth of A. flavus AYM2 in vitro. HPLC analysis revealed that T. harzianum AYM3 had a biodegradation potential against AFB1. Co-culturing of T. harazianum AYM3 and A. flavus 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 A. flavus AYM2 revealed the downregulating effects of T. harzianum AYM3 metabolites on expression of aflP and aflS genes. Using HepaRG cell line, the cytotoxicity assay indicated that T. harazianum AYM3 metabolites were safe. Based on these results, it can be concluded that T. harzianum AYM3 may be used to suppress AFB1 production in maize grains.

Co-occurrence of mycoflora, aflatoxins and fumonisins in maize and rice seeds from markets of different districts in Cairo, Egypt.

The mycoflora and mycotoxins contamination of commercial maize and rice grains collected from local markets of the major five zones of the province of Cairo, Egypt, represented by 20 different districts were studied. A total number of about 23 species belonging to 12 different genera of fungi were isolated and identified. About 70% of the samples were infected with Aspergillus flavus and Aspergillus niger, with percentages of 33%, 40% recovered from maize and 46%, 27% recovered from rice, respectively. The percentages of infection of maize ranged from 16% to 142%. The percentages of infection of rice seeds ranged from 6% to 93%. Total aflatoxins and fumonisins detected in maize averaged 9.75 and 33 µg/kg, respectively. Total aflatoxins and fumonisins detected in rice averaged 5.15 and 1014 µg/kg, respectively.