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

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.