Biological detoxification of mycotoxins by treatment with microbial enzymes

This study investigates elimination of aflatoxin B1 (AFB1) and fumonisin B1 (FB1) by treatment with recombinant enzyme preparations. Biological degradation of AFB1: Recombinant 2,3-dihydroxybiphenyl 1,2-dioxygenase (2,3-DHBD) and dihydrodiol dehydrogenase (DHD) enzymes were produced through extracellular expression of respectively the bphC1 and bphB genes of R. erythropolis in Escherichia coli BL21 (DE3). The recombinant 2,3-DHBD enzyme exhibited an enzyme activity of 34 mU/L and the combined 2,3-DHBD and DHD fractions an activity of 38 mU/L. A significant (P<0.0001) reduction in AFB1 concentration was observed when treated with extracellular culture fractions containing recombinant 2,3-DHBD, with only 50% AFB1 remaining after 72 h. The degradation of AFB1 coincided with a 40% loss of mutagenicity of AFB1 and its breakdown products as evaluated by the Salmonella typhimurium mutagenicity assay. Biological degradation of FB1: Fungal strains capable of degrading FB1 were selected by screening isolates from culture collections and compost-rich soil following enrichment techniques. Selection was based on the ability to utilize molecules containing a terminal end amino group such as [2-amino-3-hydroxy butyl (AHB)] related to FB1 as the sole nitrogen source. Aspergillus niger CBS 513.88 was able to maintain growth in a minimal growth medium with AHB and FB1 as sole nitrogen source. A. niger genes encoding degradation enzymes (carboxylesterases and aminotransferases) were expressed in Saccharomyces cerevisiae, a food-grade yeast with Generally Regarded As Safe (GRAS) status. Expression of bacterial and fungal enzymes in S. cerevisiae could support the development of safe recombinant cultures and enzymatic preparations for degrading mycotoxins in food and feed.