Vertical and horizontal distributions of clinical antibiotic resistance genes and bacterial communities in Danjiangkou Reservoir, China

The Danjiangkou Reservoir is an important water source for the middle route of the South-to-North Water Diversion Project in China. The current anthropogenic pollution of this reservoir is a great public health concern. Therefore, the horizontal and vertical distributions of seven clinical antibiotic resistance genes (ARGs) and bacterial communities in the Danjiangkou Reservoir were investigated using qPCR and next-generation sequencing, respectively. The average relative abundance of ARGs was 3.01 × 10-4 to 1.90 × 10-3 and 4.66 × 10-4 to 1.85 × 10-3 in horizontal and vertical profiles, respectively. There was a significant difference in the vertical composition of ARGs, which was caused by different media (i.e. water column vs. sediment). No significant differences in the composition of ARGs were found in the horizontal profile. Proteobacteria was the most abundant phylum, followed by Actinobacteria in the Danjiangkou Reservoir. The beta diversity pattern of the microbial communities in the vertical profile was consistent with that of the ARGs. Moreover, a significant difference in the horizontal composition of the bacterial communities among these water columns was found. All of these factors have resulted in noticeably different co-occurrence patterns of ARGs and bacterial communities between water columns and surface sediment samples. ARGs were closely associated with Proteobacteria and Chloroflexi in the sediment samples, indicating potential anthropogenic pollution in the Danjiangkou Reservoir. Although there was no significant correlation between the occurrence of ARGs and 11 opportunistic pathogens, our results point to potential risks for the development of multi-resistant pathogens due to the simultaneous presence of ARGs and pathogens in the study area. These results provide a good basis for thorough ecological evaluation and remediation of the Danjiangkou Reservoir.