THE BEHAVIOR OF POLYPHOSPHATE ACCUMULATING ACINETOBACTER ISOLATES IN AN ANAEROBIC-AEROBIC CHEMOSTAT

The presence of a specialized physiological group, the so-called ''pol y-P bacteria'', in activated sludge has been proposed to explain the u ptake of organic carbon sources under anaerobic conditions and the cyc lic release and uptake of phosphate in activated-sludge plants showing enhanced biological phosphate removal (EBPR). Members of the genus Ac inetobacter have been considered to play a role in these processes, al though their importance has been questioned. Indeed, the ability of Ac inetobacter to alternately accumulate polyhydroxyalkanoates under anae robic conditions and polyphosphate under aerobic conditions has not be en demonstrated. In this study, under aerobic batch-culture conditions , two strains of Acinetobacter which had been isolated from treatment plants exhibiting EBPR were shown to accumulate high levels of polypho sphate or a ''lipid'' reserve which in one strain was identified as a polyhydroxyalkanoate. When cultured in a chemostat which allowed cycli c exposure to anaerobic and aerobic conditions, neither of the two str ains showed release of phosphate or uptake of acetate under anaerobic conditions. These findings suggest that the behaviour of these strains does not conform to the usually accepted models for poly-P bacteria i n EBPR systems. Nevertheless, strains of Acinetobacter which accumulat e high levels of polyphosphate may still contribute to phosphate remov al in EBPR systems. (C) 1998 Elsevier Science Ltd. All rights reserved .