Niche formation of Rozellomycota in wastewater treatment model reactors

A comprehensive understanding of microbial processes is a vital objective of wastewater treatment research efforts. The fungal phylum Rozellomycota is consistently 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 abundances and roles of Rozellomycota as dominant eukaryotes in wastewater treatment model reactors. Replicated down-flow hanging sponge reactor systems, chemical water parameter surveillance, quantitative and qualitative DNA and cDNA analysis, and abundance correlations were used. Rozellomycota 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 from day 6 onwards, but a temporal succession within the reactor biofilms. The highest diversity of Rozellomycota was found between operation days 13 and 27. Within the experiment, we found single correlations between Rozellomycota, Bacteria, and Ciliophora, pointing to biotic linkages. Furthermore, we found a negative correlation with nitrogen. The high abundance of Rozellomycota in all samples indicates their distinct role in wastewater biofilms. Those insights into the complex communities can ultimately help optimize wastewater treatment processes.