Effect of continuous application of pig manure on soil antibiotic resistance genes

The large-scale application of livestock and poultry manure in protected agriculture is common; however, research on the spread of antibiotic resistance genes (ARGs) from this practice remains limited. Herein, 16 S and metagenomic sequencing methods were used to investigate the effects of eight consecutive years of pig manure application on tetracycline (TC) antibiotics in protected soil and to evaluate the ecological consequences. In addition, the characteristics of soil ARGs and bacterial diversity were explored, and the potential hosts of ARGs in protected soil and the influence of environmental factors on these potential hosts and ARGs were preliminarily investigated. After 8 years of applying composted pig manure, the total tetracycline residues in the protected soil was as follows: commercial organic fertilizer soil > pig manure soil > rapeseed cake fertilizer soil. Soil enzymes indirectly affect ARG abundance by influencing the microbial community structure. g__unclassified_p__Acidobacteria and g__unclassified_c__Actinomycetia may be the two most important ARG hosts, with a highly significant positive correlation with 32 ARG subtypes. Total nitrogen (TN) and soil organic matter (SOM) significantly promoted the abundance of these two important potential hosts. Nocardioides , g__unclassified_o__Solirubrobacterales , Actinoplanes , and Methyloceanibacter are potential hosts for intI1. TC, Soil urease(S-UE), Soil acid phosphatase(ACP), Soil β-glucosidase(S- β -GC), TN, total phosphorus (TP), and SOM significantly promoted the abundance of potential intI1 hosts. Soil environmental factors collectively accounted for 72.27% of ARG variation, making them the most important factor affecting ARGs. Our research will support manure management in protected agriculture to reduce ARG spread.