Community structure and assembly of denitrifying bacteria in epiphytic biofilms in a freshwater lake ecosystem

Denitrifying bacteria are a crucial component of aquatic ecosystem in nitrogen cycle. However, the denitrifying bacterial community dynamics and structure in epiphytic biofilms remain unexplored. The abundance of denitrification gene (nir) and structure of nirS-denitrifying bacterial community in the epiphytic biofilms collected in July and November of 2018 from a typical plateau lake (Caohai Wetland, Guizhou, China) were studied by Real-time Quantitative Polymerase Chain Reaction (qPCR) and high-throughput sequencing. Results show that the gene abundance of nirK was higher than that of nirS (P<0.05), and it was significantly different during the growth period (July) than the decline period (November). The denitrifying bacterial species was similar in the two months and shared 76.18% of OTUs. Proteobacteria (56.55%+/- 22.15%) was the dominant phylum in all the samples. Epiphytic biofilms between growth period and decline period displayed significantly different microbial community structures due to differences in species abundance. Water temperature was the crucial factor that affected the denitrifying microbial community structure in our study. Environmental factors explain only partially the dynamic characteristics of denitrifying microbial communities, implying that the stochastic processes affected the construction of denitrifying microbial communities. As the null model analysis results show, dispersal limitation (stochastic) and undominated processes significantly influenced the assembly of denitrifying microbial communities. This study broadened our understanding of the denitrifying bacterial community structure and its function on epiphytic biofilms in freshwater ecosystems with new information provided.