Microbial community diversity and tetracycline resistance gene abundance in manure-soil model under chlortetracycline stress

Objective  To explore the effects of chlortetracycline on microflora diversity and tetracycline resistance gene (TRG) abundance in manure-soil environment.

Method  Four different chlortetracycline dosages were adopted, including 0 (control), 10, 100, 1 000 μg. Samples were collected on the 1st, 7th, 14th, 28th and 56th day. High-throughput sequencing and qPCR were utilized to investigate the changes of microbial community diversity and TRG abundance.

Result  Firmicutes could tolerate toxic effect of 10 μg chlortetracycline, and was sensitive to 100 and 1 000 μg chlortetracycline. Actinobacteria could tolerate toxic effects of 100 and 1 000 μg chlortetracycline, its survival and reproduction had some advantages. The relative abundances of proteobacteria in all chlortetracycline groups on the 28th day were significantly lower than that of control group, and usually significantly higher than control group on other sampling dates. Three TRGs (tetO, tetTand tetW) were detected in chlortetracycline-manure-soil model, their changing trends of abundance were similar. Compared with the 1st day, the relative abundances in all groups on the 56th day decreased significantly. The day dissipation rates in 10 μg chlortetracycline group were significantly higher than other groups in period Ⅱ, while their relative abundances on the 7th day were significantly higher. The day dissipation rates in 100 μg chlortetracycline groups were significantly lower than other groups in period Ⅳ, while the relative abundances on the 56th day were significantly higher.

Conclusion  In manure-soil environment, the sensitivity degrees of different bacterium communities to chlortetracycline stress were different, chlortetracycline can change microbial community composition by changing the relative abundances of dominant bacteria. Chlortetracycline stress can change the day dissipation rates of TRGs, thereby affect the relative abundances of TRGs. The results can provide a basis for further research on ecological risk evaluation of antibiotic residue in poultry raising.