Isolation and Characterization of a Novel Fungus, Rhizopus arrhizus MNQW, for Effective Biodegradation and Detoxification of Zearalenone

Zearalenone (ZEN) is a prevalent estrogenic mycotoxin in cereals and feedstuffs, posing persistent risks to feed safety and animal health. In this study, a food-grade filamentous fungus, Rhizopus arrhizus MNQW, was isolated from a traditional rice starter ( Xiaoqu ) and systematically evaluated for its ZEN biodegradation capacity and practical applicability. Strain MNQW efficiently removed over 98% of 5 mg/L ZEN in minimal salt medium within 36 h under mild fermentation-compatible conditions. Subcellular fractionation and inhibition assays indicated that ZEN degradation was predominantly mediated by heat- and protease-sensitive intracellular enzymes. UPLC–MS/MS analysis revealed only transient formation of α-zearalenol at trace levels, followed by complete detoxification without accumulation of estrogenically active intermediates. In vitro bioassays using estrogen receptor-positive (ER-positive) MCF-7 and HepG2 cells confirmed that the final degradation products exhibited neither estrogenic activity nor cytotoxicity. Importantly, application of MNQW in solid-state fermentation of ZEN-contaminated maize flour (3 mg/kg) achieved approximately 97% toxin removal within 36 h while simultaneously improving nutritional quality, including increased crude protein, vitamin B ₂ , folate, and beneficial fatty acids. Whole-genome analysis identified multiple oxidoreductase- and hydrolase-encoding genes potentially involved in ZEN biotransformation. Collectively, these findings demonstrate that R. arrhizus MNQW represents a safe, efficient, and application-ready microbial candidate for detoxification and value-added processing of ZEN-contaminated feed materials.