Abstract
Animal manure comprises an important reservoir for antibiotic resistance genes (ARGs), but the variation in ARGs during anaerobic digestion at various temperatures and its underlying mechanism remain unclear. Thus, we performed anaerobic digestion using dairy manure at three temperature levels (moderate: 20 °C, mesophilic: 35 °C, and thermophilic: 55 °C), to analyze the dynamics of ARGs and bacterial communities by quantitative PCR and 16S rRNA gene sequencing. We found that 8/10 detected ARGs declined and 5/10 decreased more than 1.0 log during thermophilic digestion, whereas only four and five ARGs decreased during moderate and mesophilic digestion, respectively. The changes in ARGs and bacterial communities were similar under the moderate and mesophilic treatments, but distinct from those in the thermophilic system. Potential pathogens such as Bacteroidetes, Proteobacteria, and Corynebacterium were removed by thermophilic digestion but not by moderate and mesophilic digestion. The bacterial community succession was the dominant mechanism that influenced the variation in ARGs and integrons during anaerobic digestion. Thermophilic digestion decreased the amount of mesophilic bacteria (Bacteroidetes and Proteobacteria) carrying ARGs. Anaerobic digestion generally decreased the abundance of integrons by eliminating the aerobic hosts of integrons (Actinomycetales and Bacilli). Thermophilic anaerobic digestion is recommended for the treatment and reuse of animal manure.
Highlights
We detected diverse and abundant antibiotic resistance genes (ARGs) in dairy manure, which was consistent with previous studies[7,28,29], thereby indicating the importance of animal manure as a reservoir for ARGs
Many different types of ARGs can be found in wastewater sludge, but the most common ARG types observed in animal manure are tetracycline resistance genes and sulfonamide resistance genes[30,31,32]
Diehl and Lapara[17] showed that mesophilic anaerobic digestion removed most of the tet genes, whereas an enrichment effect was obtained under mesophilic digestion in the present study
Summary
The dynamics of ARGs during anaerobic digestion have received little study, and the underlying mechanism responsible for the variation in ARGs are not fully revealed. Bacteria are the main carriers of ARGs and the changes in the bacterial community may lead to variations in the abundance of ARGs. we hypothesized that changes in the bacterial community comprise the main mechanism responsible for variation in ARGs during anaerobic digestion, where different temperatures will shape distinct bacterial communities with diverse effects on ARGs. The objectives of the present study were: (1) to compare the variation of ARGs in dairy manure under moderate (20 °C), mesophilic (35 °C), and thermophilic (55 °C) anaerobic digestion; and (2) to explore the relationships among the chemical properties, bacterial communities, and ARGs during anaerobic digestion. The results of this study may help to enhance the reduction of ARGs from animal manure by anaerobic digestion, thereby reducing the environmental risk due to ARGs
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
