Effect of thermal stratification on denitrifying bacterial community in a deep drinking water reservoir

Abstract Seasonal thermal stratification is an important hydrological characteristic of deep reservoirs, which can influence the chemical parameters of vertical water layers. However, the effect of thermal stratification on denitrifying bacterial community is still unclear. Here, we investigated the dynamics of nirS gene abundance and the structure and composition of nirS-type denitrifying bacterial community in a deep drinking water reservoir by quantitative PCR and high-throughput sequencing, respectively. The results showed that the abundance of nirS gene was approximately 105 copies/mL, and it was significantly higher in the metalimnion and hypolimnion than that of the epilimnion layer. Proteobacteria was the predominant phylum, with high abundance of the members of Burkholderiales and Rhodocyclales at order level. Twenty dominant genera were detected in the sequences analyzed among them five genera accounted for approximately 92% of classified sequences. The network analysis (NKA) showed that the co-existence and the interaction among the nirS-type denitrifying bacteria in the Jinpen Reservoir may be crucial for the regulation of the nitrogen-cycle and water quality. Structural equation model (SEM) illustrated that temperature and dissolved oxygen had great impact on the nirS-type denitrifying bacterial community during thermal stratification. Taking together, these results provide new evidence for the ecological distribution of nirS-type denitrifying bacterial community in reservoir ecosystem, reinforcing the recent findings on the linkages between the environmental factors and denitrifying bacterial community interactions in a deep drinking water reservoir during stratification.