McIlroy, Simon Jon2; Albertsen, Mads2; Andresen, Eva Kammer1; Saunders, Aaron Marc2; Kristiansen, Rikke5; Stokholm-Bjerregaard, Mikkel2; Nielsen, Kåre Lehmann2; Nielsen, Per Halkjær1
1 Department of Chemistry and Bioscience, The Faculty of Engineering and Science, Aalborg University, VBN2 Section of Biotechnology, The Faculty of Engineering and Science, Aalborg University, VBN3 The Faculty of Engineering and Science (ENG), Aalborg University, VBN4 Section of Biology and Environmental Science, The Faculty of Engineering and Science, Aalborg University, VBN5 EcoDesign, The Faculty of Engineering and Science, Aalborg University, VBN6 Microbial Communities, The Faculty of Engineering and Science, Aalborg University, VBN
The glycogen-accumulating organism (GAO) ‘Candidatus Competibacter’ (Competibacter) uses aerobically stored glycogen to enable anaerobic carbon uptake, which is subsequently stored as polyhydroxyalkanoates (PHAs). This biphasic 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 subgroups 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 and Entner–Doudoroff glycolytic pathways, as well as for denitrification, nitrogen fixation, fermentation, trehalose synthesis and utilisation of glucose and lactate. Genetic comparison of P metabolism pathways with 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 provide new insights into the complex interaction and niche competition between PAOs and GAOs in EBPR systems.