Polyphosphate kinase, one of the key enzymes for polyphosphate accumulation in bacteria, has been investigated in pure culture and activated sludge samples. Three bacterial species (Acinetobacter lwoffi, A. phosphadevorus and Pseudomonas fluorescens) appeared to have a polyphosphate kinase activity (between 0.3 and 4.7 nM of P04 transferred per minute and per mg of proteins). However tests carried out on Aeromonas hydrophila, Bacillus subtilis, E. coli and Serratia sp. showed these species did not have any measurable polyphosphate kinase activity.

Enzyme activity in bacteria is dependent on environmental conditions and can be induced, in particular, by anaerobic stress, even without modification of extracellular phosphate concentrations. Most of the activated sludge samples taken from laboratory pilot plants achieving good phosphorus removal did not present any measurable polyphosphate kinase activity. Such poor results can be related to low numbers of phosphorus removing bacteria and inhibitory molecules in sludge extracts. The only observed activity was in pretreated sludges (washed sludges) and in sludges submitted in a batch reator to phosphate starvation. However, in these, enzyme activity was at least 20 times lower than those measured in pure culture of A. lwoffi.

Polyphosphate kinase induction is a complicated and time consuming method which has to be used only in the research field. At the present time our results show that sludge phosphate uptake potential cannot be predicted by the measure of induction of polyphosphate kinase activity.

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