Abstract
Eukaryotes are important components of ecosystems in wastewater treatment processes. However, little is known about eukaryotic community in anaerobic wastewater treatment systems. In this study, eukaryotic communities in an up flow anaerobic sludge blanket (UASB) reactor treating domestic sewage during two years of operation were investigated using V4 and V9 regions of 18S rRNA gene for amplicon sequencing. In addition, activated sludge and influent sewage samples were also analyzed and used as the references for aerobic eukaryotic community to characterize anaerobic eukaryotes. The amplicon sequence V4 and V9 libraries detected different taxonomic groups, especially from the UASB samples, suggesting that commonly used V4 and V9 primer pairs could produce a bias for eukaryotic communities analysis. Eukaryotic community structures in the UASB reactor were influenced by the immigration of eukaryotes via influent sewage but were clearly different from the influent sewage and activated sludge. Multivariate statistics indicated that protist genera Cyclidium, Platyophrya and Subulatomonas correlated with chemical oxygen demand and suspended solid concentration, and could be used as bioindicators of treatment performance. Uncultured eukaryotes groups were dominant in the UASB reactor, and their physiological roles need to be examined to understand their contributions to anaerobic processes in future studies.
Highlights
Microbial eukaryotes play important roles in wastewater treatment systems
Eukaryotic community structures were analyzed for 10 samples from a up flow anaerobic sludge blanket (UASB) reactor (Fig. 1a), influent sewage, and activated sludge, based on 18S rRNA gene sequencing
To the best of our knowledge, this is the first study of eukaryotic communities involved in anaerobic wastewater treatment that were characterized by comparison between the UASB reactor and influent sewage based on 18S rRNA gene sequencing analysis
Summary
Microbial eukaryotes play important roles in wastewater treatment systems. In particular, bacterivory by protists contributes to the reduction of sludge production, the improvement of sludge sedimentation, and the quality of effluent water[1,2,3]. A number of recent studies have used different variable regions within the 18S rRNA gene for amplification, including V1-V215, V316, V4, and V9 regions[17] Both V4 and V9 regions have been used to describe the diversity and variation of eukaryotes found in aerobic wastewater treatment systems[18,19]. In contrast to aerobic eukaryotes, limited information is available on the eukaryotic community structures found in anaerobic wastewater treatment systems Microbial eukaryotes such as protists and fungi exist and contribute to the degradation of organic matter in anaerobic wastewater treatment systems[20,21]. 18S rRNA gene amplicon sequencing has been applied to investigate eukaryotic communities in anaerobic environments such as marine[17] and rumen environments[24], few studies have used this method for anaerobic wastewater treatment systems[25]. To characterize the anaerobic eukaryotes involved in wastewater treatment, this issue must be considered
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