Transformation of antibiotics to non-toxic and non-bactericidal products by laccases ensure the safety of Stropharia rugosoannulata

The substantial use of antibiotics contributes to the spread and evolution of antibiotic resistance, posing potential risks to food production systems, including mushroom production. In this study, the potential risk of antibiotics to Stropharia rugosoannulata, the third most productive straw-rotting mushroom in China, was assessed, and the underlying mechanisms were investigated. Tetracycline exposure at environmentally relevant concentrations (<500 μg/L) did not influence the growth of S. rugosoannulata mycelia, while high concentrations of tetracycline (>500 mg/L) slightly inhibited its growth. Biodegradation was identified as the main antibiotic removal mechanism in S. rugosoannulata, with a degradation rate reaching 98.31 % at 200 mg/L tetracycline. High antibiotic removal efficiency was observed with secreted proteins of S. rugosoannulata, showing removal efficiency in the order of tetracyclines > sulfadiazines > quinolones. Antibiotic degradation products lost the ability to inhibit the growth of Escherichia coli, and tetracycline degradation products could not confer a growth advantage to antibiotic-resistant strains. Two laccases, SrLAC1 and SrLAC9, responsible for antibiotic degradation were identified based on proteomic analysis. Eleven antibiotics from tetracyclines, sulfonamides, and quinolones families could be transformed by these two laccases with degradation rates of 95.54-99.95 %, 54.43-100 %, and 5.68-57.12 %, respectively. The biosafety of the antibiotic degradation products was evaluated using the Toxicity Estimation Software Tool (TEST), revealing a decreased toxicity or no toxic effect. None of the S. rugosoannulata fruiting bodies from seven provinces in China contained detectable antibiotic-resistance genes (ARGs). This study demonstrated that S. rugosoannulata can degrade antibiotics into non-toxic and non-bactericidal products that do not accelerate the spread of antibiotic resistance, ensuring the safety of S. rugosoannulata production.