This strongly indicates that Rhodocyclus-related PAO were able to denitrify and thus played a role in the denitrification occurring in full-scale EBPR plants.Īmann, R. Furthermore, in the presence of acetate growth was sustained by using oxygen, as well as nitrate or nitrite, as an electron acceptor. The Rhodocyclus-related PAO were able to take up orthophosphate and accumulate polyphosphate when oxygen, nitrate, or nitrite was present as an electron acceptor. Glycolysis, and not the tricarboxylic acid cycle, was the source that provided the reducing power needed by the Rhodocyclus-related PAO to form the intracellular polyhydroxyalkanoate storage compounds during anaerobic substrate assimilation. Glucose could not be assimilated by the Rhodocyclus-related PAO, but it was easily fermented in the sludge to products that were subsequently consumed.

Leucine and thymidine could not be assimilated as sole substrates and could only be assimilated as cosubstrates with acetate, perhaps serving as N sources. They were able to assimilate two substrates (e.g., acetate and propionate) simultaneously. Rhodocyclus-related PAO were able to accumulate short-chain substrates, including acetate, propionate, and pyruvate, under anaerobic conditions, but they could not assimilate many other low-molecular-weight compounds, such as ethanol and butyrate.

The behavior of these bacteria generally was consistent with the biochemical models proposed for PAO, based on studies of lab-scale investigations of enriched and often unknown PAO cultures. The investigations showed that these organisms were present in all plants examined and constituted 5 to 10, 10 to 15, and 17 to 22% of the community biomass. The ecophysiology of uncultured Rhodocyclus-related polyphosphate-accumulating organisms (PAO) present in three full-scale enhanced biological phosphorus removal (EBPR) activated sludge plants was studied by using microautoradiography combined with fluorescence in situ hybridization.

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