Niche Formation of Cryptomycota in Wastewater Treatment Model Reactors

A comprehensive understanding of microbial processes is a vital objective of wastewater treatment research efforts. The fungal phylum Cryptomycota is constantly present in relatively high abundances in wastewater treatment plants, being one of the dominant eukaryotic organisms. However, their impact is unknown. In this study, we aim to enlighten the role and function of Cryptomycota as dominant eukaryotes in wastewater treatment model reactors. Replicated down-flow hanging sponge reactor systems, chemical water parameter surveillance, quantitative and qualitative DNA and RNA analysis, and abundance correlations were used. Cryptomycota exhibited around 50 distinguishable 18S sequence variants as the second most abundant group, next to ciliates. They don't show a significant gradient over the height of the reactors, being abundant in all samples. The highest diversity of Cryptomycota was found between operation days 13 and 27. We found single correlations between Cryptomycota and Ciliophora, pointing to a parasitic lifestyle or the zooplankters feeding on them. Furthermore, we identified the sublineage LKM15 as negatively correlated with ammonium. The high abundance of Cryptomycota in all samples indicates their distinct role, apparently in relation to Ciliophora, probably regulating the primary consumer population. Those insights into the complex communities can ultimately help optimize wastewater treatment processes.