Re-appraisal of the phylogeny and fluorescence in situ hybridization probes for the analysis of the Competibacteraceae in wastewater treatment systems

Members of the family Competibacteraceae are common in wastewater treatment plants (WWTPs) designed for enhanced biological phosphorus removal (EBPR) and are putatively deleterious to the process of P removal. Their ability to accumulate large amounts of polyhydroxyalkanoates is also suggested to be of potential commercial interest for bioplastic production. In this study we have updated the 16S rRNA-based phylogeny of the Competibacter and the Plasticicumulans lineages. The former is delineated by 13 clades including two described genera; Ca.Competibacter' and Ca.Contendobacter'. The oligonucleotide probes used for detection of the family by fluorescence in situ hybridization (FISH) were re-evaluated and designed for coverage of these clades. Surveys of full-scale WWTPs based on 16S rRNA gene amplicon sequencing and FISH analysis indicate that a number of member clades always coexist, with their relative abundances varying substantially between and temporally within plants. The hypothesis that these differences are based on niche partitioning is supported by marked phenotypic differences between clades. An in-depth understanding of the ecology of the family requires further studies of the metabolism of individual clades in situ. The proposed phylogeny and FISH probes will provide the foundation for such studies.