Residual antibiotics in swine wastewater (SW) promote antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARGs), threatening the environment and human health. Anaerobic digestion (AD) is a promising green technology for treating SW, but the impact of antibiotics on the microbial community and resistome during AD is unclear.
To address this gap, anaerobic batch experiments treating SW containing different sulfonamides (SMs) were conducted, with samples collected for DNA extraction and analysis of the microbial community and antibiotic resistome. ARG-carrying mobile genetic elements (MGEs) were detected, and ARG hosts were identified using metagenomic binning.
The results showed a significant negative correlation between the Abundance-based Coverage Estimator (ACE) index and the batches, with notable variability in the Shannon index. Enterococcus emerged as the dominant genus under SMs stress. A total of 24 types and 440 subtypes of ARGs were identified, with SMs stress significantly increasing the abundance of sul1, sul2, and sul3. The highest ARG abundance was observed in the sulfamonomethoxine (SMM) group during the initial stage and in the sulfamerazine (SMR) group after long-term anaerobic culture. Plasmid identification revealed that ARGs on chromosomes are much higher than those on plasmids. However, ARGs are more likely to co-occur on plasmids. Hybrid assembly identified two complete integrons and two composite transposons. Binning reconstructed 34 and 33 medium- to high-quality ARGs host genomes from all samples, determining their taxonomic classification and potential pathogenicity.
In conclusion, SMs stress intermittently disrupts the microbial community structure during AD. ARG composition and distribution are influenced by antibiotic pressure and initial ARGs in seed sludge. Prolonged antibiotic exposure increases the risk of ARG mobilization via MGEs. Specific ARB without ARGs but with inherent resistance also require attention. This study offers new insights into the occurrence and impact of antibiotics during the AD treatment of SW.
