Abstract: 【Objective】 To provide an efficiently and eco-friendly solution for elimination of antibiotics in the soils and find a foundation for the evaluation of antibiotics contaminated land, this study was carried out about the residue of antibiotics in soils and their impacts on the abundance, diversity and composition of soil bacterial community. 【Method】 In this study, two types of antibiotics (gentamicin and tylosin) and two antibiotic-degrading microbe (a fungus named Aspergillus Terreus FZC3 to degrading gentamicin, a bacterium named Achromobacter to degrading tylosin) were selected to mix in spinach-growing soil. There were 7 treatments in total, including gentamicin (CG), gentamicin and FZC3 (CGF), tylosin (CT), tylosin and Achromobacter (CTW), two antibiotics (CM), two antibiotics and their degrading microbe (CMM), and blank control (CC). Solid phase extraction and HPLC-MS/MS technology were employed to study the impacts of degrading-microbe on antibiotics. The interactive influence of antibiotics and their degrading-microbe on soil bacterial community were studied by Illumina high-throughput sequencing technologies. 【Result】 Antibiotic-degrading microbe could improve the removal of the two antibiotics in the soil, but as time went by, the differences in the residual rates of antibiotics among all the treatments gradually minimized. During the entire test period, the differences of antibiotics residual rates between treatments were most significant in the first week. Under the CMM treatment, which spiked with two antibiotics and their degrading microbe, the residual rate of gentamicin was lowest (53.93%). Under the CTW treatment, which only spiked tylosin and Achromobacter, the residual rate of tylosin was as low as 3.92%. In the first week, the residual rate of gentamicin under the CGF treatment (spiked with gentamicin and FZC3) decreased about 3.3% compared with the CG treatment (spiked with gentamicin), and the residual rate of tylosin under the CTW treatment decreased about 4.1% compared with the CT treatment (spiked with tylosin). According to the results of high-throughput sequencing, there were significant differences (P＜0.05) between the bacterial richness and diversity in the three treatments of CG, CTW and CMM, compared with CC. Comparing the samples of the first week, the relative abundances of Massilia, Bacillus and etc. under the CG treatment were significantly lower than those in CC treatment; the relative abundance of Massilia in CT treatment was significantly lower than that in the CC treatment; but the decrease of inhibitory effects of antibiotics on these bacteria in the second week, indicating that gentamicin and tylosin in the early period of pot experiment had a greater impacts on soil bacterial communities. The bacterial community structure under the CGF treatment was similar to that under the CC treatment within the fortnight, indicating that gentamicin-degrading fungus FZC3 could alleviate the inhibitory effects of gentamicin on bacteria. In contrast with CT treatment, the relative abundance of Achromobacter was significantly increased while other genus decreased under the CTW treatment, indicating that the tylosin-degrading bacteria had a greater impact on the bacterial community structure. There was no significant difference in bacterial richness, diversity and community structure within fortnight between CC treatment and CM treatment (spiked with two antibiotics), indicating that there might be an antagonistic effect in soil bacteria when gentamicin and tylosin were added simultaneously. 【Conclusion】 Residues of gentamicin and tylosin in soil had different degrees of influence on bacterial abundance, diversity, and structure in soils. The addition of exogenous antibiotic-degrading microbe would not only speed up the removal efficiency of the two antibiotics, but also alleviate the effect of antibiotics on soil bacterial communities to some extent.

Key words: gentamicin, tylosin, antibiotic-degrading microbe, bacterial diversity, spinach