Filamentous bacteria ( FB ) overgrowth is an important cause of sludge bulking in wastewater treatment plants ( WWTPs ) . However, to date, methods for the cultivation and preservation of isolated FB in the laboratory have not been completely described. Furthermore, research on whether FB can function as phosphorus accumulating organisms( PAOs) is limited. In this study, a pure strain, a Pseudomonas putida PAO-1 ( P. putida PAO-1) isolate with phosphorus removal functions was isolated from the biofilm of an alternating anaerobic/aerobic biofilter ( AABF ) , and its physiological characteristics were studied. Nitrate or nitrite could be used by the strain P. putida PAO-1 as electron acceptors for denitrification during phosphorus anoxic uptake, and 0. 63 mg NO-3-N was consumed to reduce 1 mg soluble orthophosphate ( SOP ) by P. putida PAO-1. The strain P. putida PAO-1 consumed phosphorus within the optimal pH range of 6 to 8 and the temperature range of 25 ℃ to 35 ℃. Cell deformity was a main morphological trait of the strain P. putida PAO-1, and it could elongate ( with an elongation rate of 300％-500％) when it was subjected to oligotrophic or high-salt stress ( 15 g·L-1 NaCl ) . The findings in this study provide a microbiological reference for understanding the special characteristics of a denitrifying PAO.