Abstract
Enhanced biological phosphorus removal (EBPR) is widely used to remove phosphorus from wastewater. The process relies on polyphosphate accumulating organisms (PAOs) that are able to take up phosphorus in excess of what is needed for growth, whereby phosphorus can be removed from the wastewater by wasting the biomass. However, glycogen accumulating organisms (GAOs) may reduce the EBPR efficiency as they compete for substrates with PAOs, but do not store excessive amounts of polyphosphate. PAOs and GAOs are thought to be phylogenetically unrelated, with the model PAO being the betaproteobacterial “Candidatus Accumulibacter phosphatis” (Accumulibacter) and the model GAO being the gammaproteobacterial “Candidatus Competibacter phosphatis”. Here, we report the discovery of a GAO from the genus Propionivibrio, which is closely related to Accumulibacter. Propionivibrio sp. are targeted by the canonical fluorescence in situ hybridization probes used to target Accumulibacter (PAOmix), but do not store excessive amounts of polyphosphate in situ. A laboratory scale reactor, operated to enrich for PAOs, surprisingly contained co-dominant populations of Propionivibrio and Accumulibacter. Metagenomic sequencing of multiple time-points enabled recovery of near complete population genomes from both genera. Annotation of the Propionivibrio genome confirmed their potential for the GAO phenotype and a basic metabolic model is proposed for their metabolism in the EBPR environment. Using newly designed fluorescence in situ hybridization (FISH) probes, analyses of full-scale EBPR plants revealed that Propionivibrio is a common member of the community, constituting up to 3% of the biovolume. To avoid overestimation of Accumulibacter abundance in situ, we recommend the use of the FISH probe PAO651 instead of the commonly applied PAOmix probe set.
Highlights
Enhanced biological phosphorus removal (EBPR) is employed worldwide to remove carbon, nitrogen, and phosphorus (P) from wastewater
We describe the finding of a novel glycogen accumulating organisms (GAOs) from the genus Propionivibrio that is closely related to the model polyphosphate accumulating organisms (PAOs) Accumulibacter
In this study a lab-scale sequencing batch reactor (SBR), seeded with full-scale activated sludge, was operated for a 3-month period to enrich for Accumulibacter PAOs
Summary
Enhanced biological phosphorus removal (EBPR) is employed worldwide to remove carbon, nitrogen, and phosphorus (P) from wastewater It functions on the principle of enriching for organisms capable of storing excessive amounts of polyphosphate, which can be removed from the system by wasting the biomass (Seviour et al, 2003). Under the substrate rich anaerobic conditions, Accumulibacter takes up volatile fatty acids (VFAs) and stores them as polyhydroxyalkanoates (PHA) by utilizing internal pools of polyphosphate and glycogen. Recent years have seen an increase in the known phylogenetic and physiological complexity of PAOs. For example, the discovery that some members of the genus Tetrasphaera are functional PAOs challenge the conceptual PAO model devised using Accumulibacter, as Tetrasphaera utilize very different pathways in concert with polyphosphate cycling (Kong et al, 2005; Kristiansen et al, 2013; Nguyen et al, 2015). Important metabolic differences have been attributed to these clades based on enrichment studies, where fluorescence in situ hybridization (FISH) and/or ppk gene based identification was applied (Flowers et al, 2009; Slater et al, 2010; Kim et al, 2013; Welles et al, 2015), as well as the comparison of metagenome-derived genomes (Flowers et al, 2013; Skennerton et al, 2015)
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