Regulation of ARGs during the maturation phase of oxytetracycline fermentation residue composting using...

During the maturation phase of oxytetracycline fermentation residue (OFR) composting, persistently elevated levels of undegraded oxytetracycline (OTC) can lead to a resurgence of antibiotic resistance genes (ARGs). This study evaluates the feasibility and mechanisms of ARG regulation using natural zeolite (Z) and lanthanum-modified zeolite (La-Z) under conditions of ultra-high OTC stress. The results indicate that ARGs and mobile genetic elements (MGEs) were enriched during the cooling phase but decreased during maturation, with tetM, tetG, tetX, intI1, TN916, and intI2 being the predominant elements. Z induced only a transient enrichment of ARGs, while La-Z maintained higher levels of ARGs and significantly increased MGEs. Multidimensional analyses revealed that the dynamics of ARGs were primarily influenced by synergistic interactions among physicochemical factors, MGEs, and host communities, with the combined effects surpassing individual contributions. Despite La-Z's strong ability to adsorb OTC, it unexpectedly exacerbated ARG enrichment in OFR composting, primarily due to altered physicochemical conditions, prolonged antibiotic stress, and the activation of MGEs. These findings provide a feasibility assessment and a mechanistic analysis of how Z and La-Z regulate ARGs during the maturation phase of OFR composting under ultra-high OTC levels. This study highlights the dual effects of additives in this extreme exposure context and emphasises the necessity for careful evaluation of control strategies for the safe reuse of OFR.