Context. Polyphosphate accumulating organisms (PAOs) can promote P removal in enhanced biological phosphorus removal (EBPR) systems. The most commonly observed organisms thought to be PAOs are Accumulibacter and Tetrasphaera.
Gap. All Accumulibacter and Tetrasphaera are typically assumed to remove P effectively, but it is unknown if this is true. Accumulibacter is known to exhibit a glycogen accumulating organism (GAO) metabolism when influent phosphorus is limiting, but do some members of Accumulibacter and Tetrasphaera behave as GAOs even when P is not limiting?
Aim. The aim of this study was to understand if diversity within Accumulibacter and Tetrasphaera can impact P removal and therefore the success of the EBPR process.
Methods. Bioreactor enrichments for Accumulibacter or Tetrasphaera were operated under different conditions and carbon sources, with high P influents. The microbial population was identified by quantitative fluorescence in situ hybridization (for Accumulibacter Types and Tetrasphaera clades), where cloning and Sanger sequencing were performed to obtain the near-complete gene sequences necessary to detect fine-scale differences between clades and sub-clades of Accumulibacter.
Findings. Poor P removal in EBPR processes through GAO-like activity was observed and linked to organisms that are typically classified as PAOs. GAOs such as Competibacter and Defluviicoccus were not detected at significant levels in either bioreactor. Three different clusters within Accumulibacter clade IIC were identified, IICii and IICiii being linked to poor EBPR performance. The contribution of Tetrasphaera towards P removal was found to be highly dependent on the clade composition, where clade II was linked with poorer EBPR performance.
Utilization. Phylogenetic diversity at the clade or sub-clade level within Accumulibacter and Tetrasphaera showed that some of these organisms behave similarly to GAOs rather than PAOs. This study highlights the need to closely re-examine traditional interpretations regarding the link between the microbial community composition and performance of EBPR systems.
