Screening, identification, and degradation characteristics study of bacteria capable of simultaneously degrading multiple mycotoxins

Mycotoxins are a class of highly toxic metabolites produced by filamentous fungi during their growth and reproduction, which pose serious threats to food security as well as human and animal health. In this study, a mixture of zearalenone（ZEN）, aflatoxin B₁（AFB₁）, and deoxynivalenol（DON） was utilized as the sole carbon source to screen for bacteria capable of simultaneously degrading these three toxins. Bacterial strains were identified through morphological analysis, as well as 16S rDNA and gyrB sequence analysis. By examining the degradation capabilities of bacterial fermentation broth, supernatant, cell suspension, intracellular extract, and inactivated bacterial cells, we aimed to explore the degradation potential of bacterial strains towards three types of toxins and identify the active sites for their degradation. To investigate the degradation properties of the active substances, proteinase K, SDS, and heat treatments were applied to the supernatant. Degradation products were identified using Ultra-High Performance Liquid Chromatography coupled with Tandem Mass Spectrometry（UHPLC-MS/MS）. Additionally, optimization of the reaction conditions was conducted by exploring the effects of various metal ions, fermentation temperatures, and pH values to enhance the degradation efficiency of the enzymes. The results indicated that a strain of Bacillus subtilis HNGD-sg5, isolated from sweetened garlic, was capable of degrading ZEN, AFB₁, and DON, with degradation rates of 97.27%, 93.81%, and 49.74%, respectively, and degradation rates of 99.25%, 98.94%, and 29.86% for the mixed toxins. The primary active sites for the degradation of three toxins were located in the fermentation supernatant, where the bacteria exhibited some physical adsorption for ZEN degradation. Further inactivation treatments of the supernatant revealed that the bacteria primarily degraded ZEN, AFB₁, and DON into 15-OH-ZEN, AFB₁-diol, and 3-epi-DON, respectively, through extracellular enzymes. These extracellular enzymes demonstrated high-temperature resistance in the degradation of AFB₁. In the optimization experiment, Fe³⁺, Ni²⁺, Mn²⁺, and Mg²⁺ enhanced the degradation activity of the crude enzyme solution towards ZEN, while Mn²⁺, Cu²⁺, and Zn²⁺enhanced the degradation activity of the crude enzyme solution towards AFB₁, only Cu²⁺ enhanced the degradation of DON. The degradation activity of the crude enzyme solution was highest under fermentation conditions of 50 ℃ and pH 7. These findings indicate that Bacillus subtilis HNGD-sg5 has significant potential for the simultaneous degradation of ZEN, AFB₁, and DON, providing a foundation for the development of fungal toxin-degrading enzyme preparations and the subsequent exploration of related degrading enzyme genes.