“Candidatus Competibacter”-lineage genomes retrieved from metagenomes reveal functional metabolic diversity. Candidatus Contendobacter odensis Run_B_J11

The glycogen accumulating organism (GAO) “Candidatus Competibacter” (Competibacter) uses aerobically stored glycogen to enable anaerobic carbon uptake which is subsequently stored as polyhydroxyalkanoates (PHA). This bi-phasic metabolism is key for the Competibacter to survive under the cyclic anaerobic-‘feast’: aerobic-‘famine’ regime of enhanced biological phosphorus removal (EBPR) wastewater treatment systems. As they do not contribute to phosphorus (P) removal, but compete for resources with the polyphosphate accumulating organisms (PAO), thought responsible for P removal, their proliferation theoretically reduces the EBPR capacity. In this study, two complete genomes from Competibacter were obtained from laboratory-scale enrichment reactors through metagenomics. Phylogenetic analysis identified the two genomes, “Candidatus Competibacter denitrificans” and “Candidatus Contendobacter odensis”, as being affiliated with Competibacter-lineage sub-groups 1 and 5, respectively. Both have genes for glycogen and PHA cycling and for the metabolism of volatile fatty acids. Marked differences were found in their potential for the Embden-Meyerhof-Parnas (EMP) and Entner-Doudoroff (ED) glycolytic pathways, denitrification, nitrogen fixation, fermentation, trehalose synthesis and utilization of glucose and lactate. Genetic comparison of P metabolism pathways to sequenced PAOs, revealed the absence of the Pit phosphate transporter in the Competibacter-lineage genomes – identifying a key metabolic difference with the PAO physiology. These genomes are the first from any GAO organism and they provide new insights into the complex interaction and niche competition between PAOs and GAOs in EBPR systems.