Efficient Degradation of Aflatoxin B1 and Zearalenone by Laccase-like Multicopper Oxidase from Streptomyces thermocarboxydus in the Presence of Mediators

Abstract

Multicopper oxidases (MCOs) are a diverse group of enzymes that could catalyze the oxidation of different xenobiotic compounds, with simultaneous reduction in oxygen to water. Aside from laccase, one member of the MCO superfamily has shown great potential in the biodegradation of mycotoxins; however, the mycotoxin degradation ability of other MCOs is uncertain. In this study, a novel MCO-encoding gene, StMCO, from Streptomyces thermocarboxydus, was identified, cloned, and heterologously expressed in Escherichia coli. The purified recombinant StMCO exhibited the characteristic blue color and bivalent copper ion-dependent enzyme activity. It was capable of oxidizing the model substrate ABTS, phenolic compound DMP, and azo dye RB5. Notably, StMCO could directly degrade aflatoxin B1 (AFB1) and zearalenone (ZEN) in the absence of mediators. Meanwhile, the presence of various lignin unit-derived natural mediators or ABTS could significantly accelerate the degradation of AFB1 and ZEN by StMCO. Furthermore, the biological toxicities of their corresponding degradation products, AFQ1 and 13-OH-ZEN-quinone, were remarkably decreased. Our findings suggested that efficient degradation of mycotoxins with mediators might be a common feature of the MCOs superfamily. In summary, the unique properties of MCOs make them good candidates for degrading multiple major mycotoxins in contaminated feed and food.

Aflatoxin Decontamination in Maize Steep Liquor Obtained from Bioethanol Production Using Laccases from Species within the Basidiomycota Phylum

“…Acetosyringone and syringaldehyde, used as redox mediators, were the most effective at reducing AFB 1 , with percentages ranging between 68 and 90%. In studies using bacterial laccases, VA exhibited effectiveness in reducing AFB 1 , with reduction levels of 60 and 76% [ 62 , 63 ].…”

“…Due to the redox potential of laccases that allows them to degrade a wide range of aromatic compounds, their role in the biotransformation of mycotoxins has recently been investigated [ 39 , 48 , 59 , 60 , 61 , 62 , 63 ]. Besides the great variety of compounds that laccases may oxidise, sometimes, synthetic or natural redox mediators may facilitate substrate oxidation by transferring electrons [ 48 , 64 , 65 , 66 ].…”

Advanced mycotoxin control and decontamination techniques in view of an increased aflatoxin risk in Europe due to climate change

“…Nonetheless, unspecific oxidation might also result in the generation of AFQ 1 , a less toxic compound, with other specific cytochrome isoforms (CYP3A4, 1A2, 3A7). Interestingly, it has been demonstrated that peroxidases and laccase-like enzymes can detoxify AFB 1 to AFQ 1 and do not activate the toxin to epoxide ( Loi et al, 2020b ; Qin et al, 2021 ). Other degradation mechanisms have been hypothesized, including the nucleophilic attack on the lactone and the furan rings, leading to their opening ( Kumar et al, 2022 ).…”

Microbial Enzymes Involved in the Biotransformation of Major Mycotoxins

“…The degradation products of DON, ZEN, and AFB 1 were C 15 H 18 O 8, 15-OH-ZEN, and AFB 1 -diol, respectively, which were all less toxic than their parent toxicants. Qin et al 94 isolated StMCO, a new multicopper oxidase (MCO), from S. thermocarboxydus. Without the aid of a mediator, StMCO could degrade AFB 1 and ZEN to AFQ1 and 13-OH-ZEN-quinone, respectively.…”