Eukaryotic communities in wastewater treatment processes as revealed by 18S rRNA gene clone library

Eukaryotic communities in two different wastewater processes, a full-scale anaerobic/aerobic activated sludge process and a pilot-scale Down-flow hanging sponge (DHS) process, was evaluated by constrcting 18S rRNA gene clone library. The clones close to the member of Opercularia was found to be a dominant eukaryote in anaerobic and aerobic activated sludges, whereas the clones affiliated to phylum Arthropoda were the most predominant in the DHS sludges. Eukaryotic communities of the activated sludges as revealed by 18S rRNA gene clone library were in agreement with published data determined by microscopic observation. On the other hand, eukaryotic communities as revealed by 18S rRNA gene clone library and microscopic observation were significantly different in the case of the DHS sluges; therefore, it was suggested that both molecular and microscopic approaches need to be conducted. The molecular approach can also reveal unidentified eukaryotic gene sequences, which might be important for understanding wastewater treatment processes.