A metabolic model for members of the genus Tetrasphaera involved in enhanced biological phosphorus removal

Abstract

Members of the genus Tetrasphaera are considered to be putative polyphosphate accumulating organisms (PAOs) in enhanced biological phosphorus removal (EBPR) from wastewater. Although abundant in Danish full-scale wastewater EBPR plants, how similar their ecophysiology is to 'Candidatus Accumulibacter phosphatis' is unclear, although they may occupy different ecological niches in EBPR communities. The genomes of four Tetrasphaera isolates (T. australiensis, T. japonica, T. elongata and T. jenkinsii) were sequenced and annotated, and the data used to construct metabolic models. These models incorporate central aspects of carbon and phosphorus metabolism critical to understanding their behavior under the alternating anaerobic/aerobic conditions encountered in EBPR systems. Key features of these metabolic pathways were investigated in pure cultures, although poor growth limited their analyses to T. japonica and T. elongata. Based on the models, we propose that under anaerobic conditions the Tetrasphaerarelated PAOs take up glucose and ferment this to succinate and other components. They also synthesize glycogen as a storage polymer, using energy generated from the degradation of stored polyphosphate and substrate fermentation. During the aerobic phase, the stored glycogen is catabolized to provide energy for growth and to replenish the intracellular polyphosphate reserves needed for subsequent anaerobic metabolism. They are also able to denitrify. This physiology is markedly different to that displayed by 'Candidatus Accumulibacter phosphatis', and reveals Tetrasphaera populations to be unusual and physiologically versatile PAOs carrying out denitrification, fermentation and polyphosphate accumulation.

Intracellular Accumulation of Glycine in Polyphosphate-Accumulating Organisms in Activated Sludge, a Novel Storage Mechanism under Dynamic Anaerobic-Aerobic Conditions

“…Accumulibacter" is controlled by the intracellular pools of poly(P) and glycogen (2,17,37,38). Glycine uptake by Tetrasphaera is likely also controlled by the amount of intracellular poly(P) available to provide energy for substrate uptake by the action of the low-affinity Pit transporter that is present in all known PAOs, including Tetrasphaera (12,35). This is also supported by the observation that uptake of glycine by both T. elongata and activated sludge showed the same saturation behavior as is known for acetate uptake in "Ca.…”

“…Figure 4A shows that T. elongata demonstrated a typical PAO phenotype, with the consumption of organics (glycine) and release of P i during the anaerobic phase and reassimilation of P i under subsequent aerobic conditions. This is known to be accumulated as poly(P) (12). The ratio between glycine taken up and released P i was 0.48 mol/mol.…”

“…Recently, Kristiansen et al (12) proposed a metabolic model for Tetrasphaera PAOs. Based on the model, Tetrasphaera-related PAOs take up glucose anaerobically and ferment this to succinate and other components.…”

“…Accumulibacter" (4,(15)(16)(17). However, all metabolic models for EBPR have been developed on acetate and glucose (11,12) and do not cover the use of amino acids. A typical P i release and uptake pattern from EBPR plants has been observed upon addition of certain amino acids under dynamic anaerobic-aerobic conditions (7,8), but the storage product(s) and metabolic pathways remain unknown.…”

Sludge bulking impact on relevant bacterial populations in a full-scale municipal wastewater treatment plant

“…are known to be the principal polyphosphateaccumulating organisms (PAOs) [27]. Candidatus Accumulibacter phosphatis (3.3-6.6%) and Tetrasphaera spp.…”