Community structure and functional diversity of epiphytic bacteria and planktonic bacteria on submerged macrophytes in Caohai Lake, southwest of China

Epiphytic bacteria on the surfaces of submerged macrophytes play an important role in lake biodiversity and ecological processes. However, compared with planktonic bacteria, there is poor understanding of the community structure and function of epiphytic bacteria. Here, we used 16S rRNA gene high-throughput sequencing and functional prediction analysis to explore the structural and functional diversity of epiphytic bacteria and planktonic bacteria of a typical submerged macrophyte (Potamogeton lucens) in Caohai Lake. The results showed that the species composition of epiphytic and planktonic bacteria was highly similar as 88.89% phyla, 77.21% genera and 65.78% OTUs were shared by the two kinds of samples. Proteobacteria and Bacteroidetes were dominant phyla shared by the two kinds of communities. However, there are also some special taxa. Furthermore, the epiphytic bacterial communities exhibited significantly different structures from those in water, and the abundant OTUs had opposite constituents. The explained proportion of the planktonic bacterial community by aquatic environmental parameters is significantly higher than that of epiphytic bacteria, implying that the habitat microenvironment of epiphytic biofilms may be a strong driving force of the epiphytic bacterial community. Functional predictive analysis (Functional Annotation of Prokaryotic Taxa, FAPROTAX) found that epiphytic bacteria and planktonic bacteria are dominated by heterotrophic functions, but epiphytic bacteria have more prominent fermentation and denitrification functions (nitrate reduction, nitrate respiration, and nitrite respiration) than planktonic bacteria. This study has increased our understanding of the communities and functions of epiphytic bacteria on submerged macrophyte leaves, and their role in lake denitrification cannot be ignored.