Enhanced freeze-thaw cycles facilitate the antibiotic resistance proliferation and dissemination risk under global climate change

Antibiotic resistance genes (ARGs) and antibiotic resistant bacteria are considered as emerging contaminants, whose proliferation and dissemination are highly related to the climate conditions. Freeze-thaw cycles (FTC) is a natural phenomena that widely occurred in terrestrial ecosystem for high latitude environments, and frequent FTC has been revealed under global climate change. However, the effects of FTC on the resistome in soil are still not clear. Thus, a simulation experiment was performed to illustrate the profiles of ARGs and mobile genetic elements (MGEs) under FTC exposure. It was found that, 56.4-73.2% of the shared 71 core ARG subtypes were enriched after FTC treatment, and the abundance of ARGs in total had a significant positive linear correlation with the number of FTC in spite of the declined number of ARG subtypes (r = 0.986, p = 0.002). This can explained by the selection pressure exert by freeze-thaw on bacterial community structure and promoted horizontal gene transfer (HGT). The bacterial classeses within phylum Actinobacteria, one of the dominate bacterial phylum accounting for 36-54% of the total bacteria, were enriched because of their spore and filamentous producing attributes, and enormous ARGs were presented in this kind of antibiotic-synthesising bacteria. Moreover, the survived Actinobacteria could serve as ARG donors and receptors, which profit the HGT of ARGs. The present study revealed the facilitation posed by FTC on the proliferation and dissemination of ARGs, and the accordingly findings provide new sights for well understanding of the environmental behaviour of ARGs.