Antibiotic resistance genes attenuated with salt accumulation in saline soil

Salt accumulation on the surface of the soil layer driven by the strong evaporation is a natural phenomenon that usually happens in the dry season, particularly on the coastal lands reclaimed from tidal flats. However, the influence of salt accumulation on the distribution profile of antibiotic resistance genes (ARGs) and mobile gene elements (MGEs) remains unclear. In this study, we sampled a wild saline soil where the salt accumulation was frequently observed to investigate the vertical distribution profiles of ARGs and MGEs. The results showed that an increasing gradient of ARGs and MGEs was observed from the top to deep layer with the decreasing of electrical conductivity (EC1:5 values) indicating the salt-influenced attenuation of ARGs in the saline soil. The competing test suggested that the attenuation of ARGs in response to salinity gradient was attributable to the elimination of the ARG-harboring plasmids, due to the reduction of the relative fitness of plasmid-harboring strains. Additionally, the network analyses showed that the attenuation of ARGs might be associated with decreased abundance of Actinobacteria. Overall, this study identifies that salinity as an abiotic stress could re-shape the distribution of ARGs, which may influence the dissemination of ARGs in the environment.