Characterization of microbes and denitrifiers attached to two species of floating plants in the wetlands of Lake Taihu

Biofilms are often observed at the solid-water interface. The leaves of many floating macrophytes have characteristics of both terrestrial plants and submerged macrophytes, because, in general, their upper and lower surfaces are exposed to air and water, respectively. However, little is known about the biofilms attached to floating plants. We investigated biofilms attached to the leaves, stems and roots of the floating plants Nymphoides peltata (in summer and winter) and Trapa natans (in summer) in the Gonghu Bay of Lake Taihu. Bacteria and algae were major components of the biofilm on the leaves of the two species of plants. In addition, 454 pyrosequencing analysis of bacterial 16S rRNA genes revealed that Proteobacteria was the dominant phylum, followed by Bacteroidetes, Firmicutes, Chloroflexi, Acidobacteria, and Verrucomicrobia. Cluster analysis showed that bacterial communities from the same plant source were clustered into the same group. A total of 677 genera were detected, and 47 genera were shared by all samples. Nitrifiers, including Nitrosomonas, Nitrosococcus and Nitrospira were detected in this study. Seven denitrifying genes (napA, napG, nirS, nirK, cnorB, qnorB and nosZ) were used to detect the abundance of denitrifiers. Genes nirK, nirS cnorB and nosZ were the four most abundant genes in all samples. Our results demonstrated that cultivation of floating plants in water column could enlarge the area for biofilm growth, and biofilms might play an important role in denitrification in eutrophic water.