Genetic diversity of eukaryotic microorganisms in Lake Taihu, a large shallow subtropical lake in China

We investigated the genetic diversity of eukaryotic microorganisms (0.8-20 mu m) by sequencing cloned 18S rRNA genes in six genetic libraries constructed from six locations in Lake Taihu, a large shallow subtropical lake in China. Genetic libraries of eukaryotic ribosomal RNA were screened by restriction fragment length polymorphism (RFLP) analysis, and one clone representative of each RFLP pattern was partially sequenced. A total of 528 clones were clustered into 165 RFLP patterns and finally into 131 operational taxonomic unit (OTUs). Phylogenetic analysis revealed that each library included many unique OTUs, as well as members of distantly related phylogenetic groups. A majority of the clones were from alveolates, stramenopiles, cercozoa, cryptophytes, chlorophytes, and fungi, with members of choanoflagellida, euglenida, centroheliozoa, ancyromonadidae, ichthyosporea, and kathablepharid representing a minor fraction of the library. Six OTUs (15 clones) were not related to any known eukaryotic group. Canonical correspondence analysis suggested that the differences in eukaryotic microorganism community composition of in the six regions were partially related to trophic status, sediment resuspension, and top-down regulation by metazooplankton.