Bacteria and Micro-Eukaryotes are Differentially Segregated in Sympatric Wastewater Microhabitats.

Wastewater purification is mostly performed in activated sludge reactors by bacterial and micro-eukaryotic communities, populating organic flocs and a watery liquor. While there are numerous molecular community studies of the bacterial fraction, those on micro-eukaryotes are rare. We performed a year-long parallel 16S rRNA gene and 18S rRNA-gene based analysis of the bacterial and of the micro-eukaryote communities, respectively, of physically separated flocs and particle-free liquor samples from three WWTPs. This uncovered a hitherto unknown large diversity of micro-eukaryotes largely composed of potential phagotrophs preferentially feeding on either bacteria or other micro-eukaryotes. We further explored whether colonization of the microhabitats was selective, showing that for both microbial communities, different but often closely taxonomically and functionally related populations exhibiting different dynamic patterns populated the microhabitats. An analysis of their between plants-shared core populations showed the micro-eukaryotes to be dispersal limited in comparison to bacteria. Finally, a detailed analysis of a weather-caused operational disruption in one of the plants suggested that the absence of populations common to the floc and liquor habitat may negatively affect resilience and stability. This article is protected by copyright. All rights reserved.