Decoding the fate of antibiotic resistance genes in soil with the application of thermally treated gentamicin mycelial residues

Gentamicin mycelium residues (GMRs) is a type of organic waste generated during the production of gentamicin. Although thermal treatment could eliminate the majority of antibiotic in GMRs, the resistance risks caused by residual gentamicin still require further investigation. This study aimed to evaluate the resistance risks of thermal-treated GMRs as a soil amendment by monitoring changes in gentamicin, resistance genes and bacterial community in the soil. The results indicated that gentamicin could be rapidly degraded in soil amended with thermal-treated GMRs (TGMRs) within 1st day, the abundance of AAC(6′)-Ie-APH (2′)-Ia, armA, APH(3′)-VI, ANT(2″)-Ia, Tn916/1545 and intIl restored to the soil background level at the 90th day. Furthermore, TGMRs could increase the abundance of soil bacteria that were beneficial for organic matter decomposition, while reducing the adverse effects of gentamicin on bacterial community diversity and richness. These findings provided more references for the environmental risk management of TGMRs in agricultural applications.