Effects of chlorotetracycline on antibiotic resistance genes and the bacterial community during cattle manure composting.

Chlorotetracycline (CTC) is one of the most antibiotics present in cattle manure. In present study, three levels of CTC (0, 20 and 40 mg kg-1) were added to cattle manure composting systems to investigate its effects on the distribution of antibiotic-resistant genes (ARGs) and succession of bacterial community. Adding CTC hindered the removal of ARGs during composting; the high level of CTC significantly increased the relative abundance (RA) of 9/11 ARGs and four MGEs. The bacterial community could be clustered according to the composting time under various treatments, with the high level of CTC having a more persistent effect on the bacterial community. Based on redundancy analysis, bacterial community explained the most variation in ARGs (50.1%), whereas based on network analysis, Firmicutes and Proteobacteria were the main hosts for ARGs. In conclusion, the presence of CTC increased the risks of spreading ARGs in compost products.