Insights into the effects of Zn exposure on the fate of tylosin resistance genes and dynamics of microbial community during co-composting with tylosin fermentation dregs and swine manure

Though heavy metals are widely reported to induce antibiotic resistance propagation, how antibiotic resistance changes in response to heavy metal abundances remains unclearly. In this study, the tylosin fermentation dregs (TFDs) and swine manure co-composting process amended with two exposure levels of heavy metal Zn were performed. Results showed that the bioavailable Zn contents decreased 2.6-fold averagely, and the removal percentage of total tylosin resistance genes was around 23.5% after the co-composting completed. Furthermore, the tylosin resistance genes and some generic bacteria may exhibited a hormetic-like dose-response with the high-dosage inhibition and low dosage stimulation induced by bioavailable Zn contents during the co-composting process, which represented a beneficial aspect of adaptive responses to harmful environmental stimuli. This study provided a comprehensive understanding and predicted risk assessment for the Zn-contaminate solid wastes deposal and suggested that low levels of Zn or other heavy metals should receive more attention for their potential to the induction of resistance bacteria and propagation of antibiotic resistance genes.

Automated summary

This study investigated the response of antibiotic resistance to heavy metal zinc in the co-composting process. The findings suggest that a decrease in bioavailable zinc content can reduce the level of tylosin resistance genes, and exposure to different levels of zinc may lead to a hormetic-like dose-response, with high doses inhibiting resistance genes and low doses stimulating their growth.