Interconversion of Tetracyclines and Their Metabolites in Chicken-Manure-Amended Soils and the Response of Bacterial Communities

Tetracyclines (TCs) are the most commonly detected antibiotics in agricultural soils due to their widespread application in animal husbandry, and the degradation and transformation of manure-derived TCs in soil are hot spots as well. To investigate the degradation dynamics and transformation products of manure-derived TCs in soil, microcosm experiments were conducted to simulate the degradation and transformation of tetracycline (TC), oxytetracycline (OTC) and chlortetracycline (CTC) in agricultural soil with chicken manure under natural conditions. The response profiles of microbial communities and the interactions between TCs and microbial communities in soil were explored via 16S rRNA gene sequencing and network analysis, respectively. The degradation of manure-derived TCs in soil followed the order of OTC > CTC > TC, and 4-epimers metabolites with concentration equal to parent TCs were most prone to emerge in soil, followed by epimer–dehydration metabolites. Based on bacterial diversity analysis, the soil bacterial community was reshaped by exogenous microorganisms introduced by chicken manure and TCs. The α-diversity was elevated, and the community composition underwent restructuring with Proteobacteria supplanting Actinobacteriota as the dominant phylum in soil. Specifically, these differential genera mainly belonged to Proteobacteria, Actinobacteriota and Firmicutes, which are potentially involved in N-cycle, oxidation, cell lysis and pollutant degradation according to function prediction. Network analysis further indicated that these genera were closely associated with the degradation and transformation of TCs in soil. Redundancy analysis (RDA) revealed that the top 15 key different bacteria explained 20.63% of total variations, and Bacillus graminis and Mesorhizobium were possible attributors of the degradation and interconversion of manure-derived TCs in soil. These findings will provide a base for researching and developing green manure inputs to reduce and control antibiotic contamination in soil.