Effects Of Superabsorbent Polymers On The Abundances Of Antibiotic Resistance Genes And The Bacterial Community During Composting

Antibiotics resistance genes?ARGs?are a category of emerging environmental pollutant,which can propagate between different microbes via mobile gene elements?MGEs?by horizontal gene transfer.If ARGs are transferred into the pathogenic bacteria,it will reduce the efficacy of antibiotic drugs and pose a serious threat to human health.Livestock manure has become an important ARGs repository.Livestock manure after composted can be applied into the farmland as organic fertilizer,but it will increase the potential risk of the propagation of ARGs at the same time.This study used superabsorbent polymers?SAPs?,a novel environmental material with adsorption properties as composting additive.The effects of adding 0?CK?,5 mg/kg?L?,and 15 mg/kg?H?SAP on the compost parameters,the concentrations of bio-Cu and bio-Zn,the abundances of ARGs and MGEs,and the microbial community during swine manure composting were studied,and the relationships between ARGs,environmental factors and microbial communities were also analyzed.The main results and conclusions are as follows:?1?The highest temperatures in three piles were 63.8?C?CK?,65.5?C?L?and 71.0?C?H?,respectively,indicating that adding 15mg/kg SAP significantly increased the compost temperature during the thermophilic phase.The pH values increased with the concentrations of SAP,indicating that adding 15mg/kg SAP significantly increased the compost pH values.H treatment significantly increased the compost moisture content,but there was no significant difference between L and CK treatments.Adding SAP significantly reduced the concentrations of bio-Cu and bio-Zn,while had no significant effect on C/N ratio.?2?The absolute abundances?AAs?of sulfonamides resistance genes dfr A7?sul1 and sul2 in H treatment were 94.98%,93.08% and 97.43% lower than that in CK treatment.The AAs of macrolide resistance genes and tetracycline resistance genes in H treatment were also significantly lower than that in CK treatment.The removal efficiency of quinolones resistance genes achieved 99% in H treatment.Adding 5mg/kg SAP only reduced the AAs of several ARGs.The results indicated that 15mg/kg SAP was the more appropriate concentration for ARGs removal.Redundancy analysis showed that the explanatory power of pH values,moisture content and temperature are relatively high in variations in ARGs and MGEs.?3?Firmicutes,Proteobacteria,Actinobacteria,and Bacteroidetes are the dominant phyla in each sample.The microbial community profiles were similar in CK and 5 mg/kg SAP treatment,while showed significant variation in 15 mg/kg SAP treatment after thermophilic phase,specifically,the abundance of Firmicutes decreased while Proteobacteria increased.Adding 15 mg/kg SAP reduced the abundances of human pathogenic bacteria Aeromonas and Corynebacterium₁.Network analysis found 9 ARGs potential host bacteria which are mainly phyla Firmicutes and Actinobacteria.The reduction of potential host bacteria may decrease the AAs of ARGs during composting.The frequent co-occurrence of ARGs and MGEs suggests that these ARGs may coexist with MGEs on the same gene fragment and be transferred and propagated with MGEs in the environment.