POLYPHOSPHATE ACCUMULATION AMONG DENITRIFYING BACTERIA IN ACTIVATED-SLUDGE

Bacterial polyphosphate accumulation and denitrification are important processes in biological removal of nutrients from wastewater. It has been suggested that phosphorus accumulators are able to denitrify. How ever, the bacteria known as the most important phosphorus accumulators , belonging to the genus Acinetobacter are generally not known to deni trify. To clarify how commonly both physiological traits are present i n the same organism, we screened 165 isolates from activated sludge an d wastewater for their ability to denitrify, and the ability of the de nitrifying isolates to accumulate polyphosphate. Of the 165 isolates, 149 were from acetate mineral medium (87 of these identified as Acinet obacter by the API 20 NE identification system) and 16 were from nutri ent broth and nitrate medium. Only 15 of 165 isolates tested showed tr ue respiratory denitrification activity. In the presence of acetylene they converted more than 80% of 5mM NO3- to N2O in 6 days. None of the Acinetobacter isolates were among the 15 respiratory denitrifiers. Th e denitrifying isolates were identified as species of Pseudomonas, Agr obacteuium, Pasteurella, Sphingomonas or could not be identified by th e API 20 NE identification system. According to the BIOLOG identificat ion system the denitrifiers were species of Pseudomonas, Hydrogenophag a, Citrobacter, Xanthomonas or they could not be identified. The abili ty of confirmed denitrifiers to accumulate phosphate was measured in e xperiments where cells pregrown under phosphorus Limitation were expos ed to phosphate (8 mg P/L) under aerobic conditions. The rates of exce ss phosphate uptake varied from 0.3 to more than 23 mg P/g dry matter/ h. Rates for four isolates were higher than those reported for Acineto bacter strains. These results show that polyphosphate accumulation and denitrification in activated sludge can be carried out by the same or ganisms.