A　new　method　using　polyphosphate　kinase　(PPK)　probe　was　developed　in　this　study　to　measure　the　ratio　of　denitrifying　phosphate-accumulating　organisms　(DNPAOs)　to　bacteria.　Advantages　and　disadvantages　of　this　method　and　previously　published　methods　were　evaluated.　Biochemical　characteristics　and　metabolic　mechanisms　of　the　bacterial　community　in　activated　sludge　were　analyzed.　The　result　indicated　that　PPK　probe　targeting　at　the　gene　of　polyphosphate　kinase　in　bacterial　cells　could　marked　more　PAOs　than　traditional　PAO　probes.　The　ratio　of　DNPAOs/bacteria　reached　60.30%　in　activated　sludge.　The　whole　bacterial　community　in　activated　sludge,　at　the　end　of　A/A　stage,　presented　significant　non　fermentative　characteristics　although　the　activated　sludge　still　contained　some　fermentative　bacteria.　Study　on　the　metabolic　mechanisms　suggested　that　intracellular　PHB　served　as　the　major　carbon　source　and　energy　source　of　bacterial　community　in　activated　sludge.　(C)　2017　Elsevier　Ltd.　All　rights　reserved.