The role of substrate types and substrate microbial community on the fate of antibiotic resistance genes during anaerobic digestion

Anaerobic digestion (AD) is regarded as a promising technology in energy recovery and the spread mitigation of antibiotic resistance. However, the performance of AD is dependent on various factors, and substrate type is one of the most important. In this study, the fate of antibiotic resistance genes (ARGs) response to the substrate types was investigated, and three typical environmental reservoirs of ARGs (pig manure, chicken manure and sewage sludge) were selected. The role of substrate microbial community on the fate of ARGs was clarified through the comparison between the AD of the substrates with and without a prior autoclave-disinfected step. Results showed that substrate types significantly influenced the fate of ARGs, while the influence from the substrate microbial community was limited. The concentration of antibiotics, the horizontal gene transfer reflected by intI1 and co-selection from heavy metals reflected by metal resistance genes (MRGs) were all reduced effectively. Microbial community varied from substrate types and dominated the ARGs fate concerning the standardized total effects through the mantel test and SEM analysis. The fate of tetX, ermF, tetM and ermB was mainly determined by the physicochemical parameters and the phyla of Firmicutes and Bacteroides. The phyla of Actinobacteria, pcoA and czcA contributed most to the reduction of blaTEM and mcr-1, and the phyla of Proteobacteria, Chloroflexi, Synergistetes, Euryarchaeote, intI1 and merA correlated significantly with the fate of blaCTX-M, ereA, tetG and sulI. This study highlighted the importance of substrate types when considering the fate of ARGs during AD.