Spatial Variation of <i>Cladophora</i> Epiphytes in the Nan River, Thailand

<i>Cladophora</i> is an algal genus known to be ecologically important. It provides habitats for microorganisms known to provide ecological services such as biosynthesis of cobalamin (vitamin B₁₂) and nutrient cycling. Most knowledge of microbiomes was obtained from studies of lacustrine <i>Cladophora</i> species. However, whether lotic freshwater <i>Cladophora</i> microbiomes are as complex as the lentic ones or provide similar ecological services is not known. To illuminate these issues, we used amplicons of 16S rDNA, 18S rDNA, and ITS to investigate the taxonomy and diversity of the microorganisms associated with replicate <i>Cladophora</i> samples from three sites along the Nan River, Thailand. Results showed that the diversity of prokaryotic and eukaryotic members of <i>Cladophora</i> microbiomes collected from different sampling sites was statistically different. Fifty percent of the identifiable taxa were shared across sampling sites: these included organisms belonging to different trophic levels, decomposers, and heterotrophic bacteria. These heterogeneous assemblages of bacteria, by functional inference, have the potential to perform various ecological functions, i.e., cellulose degradation, cobalamin biosynthesis, fermentative hydrogen production, ammonium oxidation, amino acid fermentation, dissimilatory reduction of nitrate to ammonium, nitrite reduction, nitrate reduction, sulfur reduction, polyphosphate accumulation, denitrifying phosphorus-accumulation, and degradation of aromatic compounds. Results suggested that river populations of <i>Cladophora</i> provide ecologically important habitat for microorganisms that are key to nutrient cycling in lotic ecosystems.