Exploring microbial diversity and ecological function of epiphytic and surface sediment biofilm communities in a shallow tropical lake

Microbial communities in epiphytic biofilms and surface sediments play a vital role in the biogeochemical cycles of the major chemical elements in freshwater. However, little is known about the diversity, composition, and ecological functions of microbial communities in shallow tropical lakes dominated by aquatic macrophytes. In this study, epiphytic bacterial and eukaryotic biofilm communities on submerged and floating macrophytes and surface sediments were investigated in Lake Rumira, Rwanda in August and November 2019. High-throughput sequencing data revealed that members of the phyla, including Firmicutes, Proteobacteria, Cyanobacteria, Actinobacteria, Chloroflexi, Bacteriodetes, Verrumicrobia, and Myxomycota, dominated bacterial communities, while the microeukaryotic communities were dominated by Unclassified (uncl) SAR(Stramenopiles, Alveolata, Rhizaria), Rotifers, Ascomycota, Gastrotricha, Platyhelminthes, Chloroplastida, and Arthropoda. Interestingly, the eukaryotic OTUs (operational taxonomic units) number and Shannon indices were significantly higher in sediments and epiphytic biofilms on Eicchornia crassipes than Ceratophyllum demersum (p < 0.05), while no differences were observed in bacterial OTUs number and Shannon values among substrates. Redundancy analysis (RDA) showed that water temperature, pH, dissolved oxygen (DO), total nitrogen (TN), and electrical conductivity (EC) were the most important abiotic factors closely related to the microbial community on C. demersum and E. crassipes. Furthermore, co-occurrence networks analysis (|r| > 0.7, p < 0.05) and functional prediction revealed more complex interactions among microbes on C. demersum than on E. crassipes and sediments, and those interactions include cross-feeding, parasitism, symbiosis, and predatism among organisms in biofilms. These results suggested that substrate-type and environmental factors were the strong driving forces of microbial diversity in epiphytic biofilms and surface sediments, thus shedding new insights into microbial community diversity in epiphytic biofilms and surface sediments and its ecological role in tropical lacustrine ecosystems.