FISH image of Tetrasphaera-PAO in activated sludge. Bacteria hybridizing with the bacterial probes EUBmix (green) and FISH image showing the branched rods (circles) and filament (square) hybridizing with probe Tet2-174. Yellow cells are overlay of red and green. Scale bar = 10 microns. - Source:3Aerobic heterotroph
Members of the Tetrasphaera have also been identified as PAOs, reported to cycle polyphosphate, but without PHA accumulation. Instead, they seem to mainly utilize sugars and amino acids through a fermentative metabolism, where polyphosphate supplements anaerobic energy requirements 2345. Some may also be involved in denitrification 2. Interestingly, T. elongata can accumulate assimilated carbon and metabolites intracellularly (at approx. 4 mM) under anaerobic conditions for later use when oxygen becomes available 6. Thus, members of the genus in activated sludge may utilise several physiological strategies. Some strains form filaments, eg. Eikelboom "Nostcoida limicola II" may be a Tetrasphaera 3, but rarely cause foaming or bulking problems.
3 FISH probe-defined clades (1-3) in activated sludge
Clade 1 = Tet1-266; Clade 2A = Tet2-892; Clade 2B = Tet2-174; Clade 3 = Tet3-654 3. Note that it is difficult to assess the specificity of these probes in MiDAS given they were designed against partial sequences that are not included in the database. In alternative, it is recommended the application of the probe Actino-658 5
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