Studies on polyphosphate and poly-beta-hydroxyalkanoate accumulation in Acinetobacter johnsonii 120 and some other bacteria from activated sludge in batch and continuous culture

Twelve bacterial isolates, four of them assigned to the genus Acinetobacter, were taken from sewage of a treatment plant with Enhanced Biological Phosphorus Removal (EBPR) and screened for phosphorus uptake, polyphosphate (polyP) accumulation and adsorption under limited carbon and nitrogen conditions. In addition, poly-beta-hydroxyalkanoate (PHA) production was studied under carbon, nitrogen, phosphorus, and oxygen limitation. Under C limitation, the uptake of phosphorus was highest, ranging up to 66 mg P per g dry weight (dw) for the Acinetobacter isolates, whereas the highest amount of polyP was detected under limited N conditions (up to 25 mg PolyP/g dw). Extra-cellular polyp was detected, however to a minor extent, accounting for a maximum of 10% of the total polyp in one Acinetobacter isolate. The highest PHA concentration (given as 3-hydroxybutyrate, 3 HE) with 211 mg 3 HB/g dry weight (21% of the dried cell mass) was found for A. johnsonii 120 under nitrogen limitation, but also under P and O-2 limitation, PHA, mainly poly-beta-hydroxybutyrate and poly-beta-hydroxyvalerate, were produced. Three isolates,assigned to the genus Pseudomonas, showed even higher values (345-427 mg 3 HB/g dw) under N limitation Studies with Acinetobacter johnsonii 120 in continuous culture, simulating the aerobic/anaerobic periods of a waste-water treatment plant, resulted in a P elimination of 36% at an anaerobic contact time of 0.6 h. This value increased to 51% at an anaerobic contact time of 3.1 h. No release of phosphate and no uptake of acetate could be detected during the anaerobic period. In addition, Acinetobacter johnsonii 120 was not able to synthesize PHA under anaerobic conditions. By changing the anaerobic conditions to aerobic, a continuous decrease of the polyp content relative to the total P content from 45% (day 1 of the aerobic process) to 19% (day 17 of the aerobic process) was observed. The amount of PHA increased to 50.4 mg 3 HB/g dw under aerobic conditions. The results indicate again that the EPBR process cannot be defined by simply applying the knowledge of the metabolic processes, observed or assumed in Acinetobacter pure cultures, to the complexity of the process in sewage treatment plants.