In　order　to　understand　the　enhanced　biological　phosphorus　removal　in　a　continuous-flow　domestic　wastewater　treatment　system,　population　dynamics　of　＂Candidatus　Accumulibacter　phosphatis＂　using　polyphosphate　kinase　(ppk1)　gene　as　genetic　marker　was　investigated　under　the　modes　of　complete　nitrification　and　partial　nitrification　(nitritation).　Nitritation　was　achieved　at　hydraulic　retention　time　(HRT)　of　6.49　h　and　dissolved　oxygen　(DO)　of　0.5　mg　O-2/L.　Denitrifying　phosphate　removal　via　nitrite　pathway　caused　low　PHAs　consumption.　Regardless　of　change　of　nitrifying　modes,　phosphorus　removal　always　maintained　at　a　high　level　of　about　100%.　Abundance　of　total　Accumulibacter　increased　along　with　rising　of　carbon　to　nitrogen　ratios　(C/N).　Under　good　performance　of　complete　nitrification　and　nitritation,　IIC　and　HD　Glade　affiliated　with　type　II　(including　clades　II　A-I)　of　Accumulibacter　lineage　was　dominant　(70%-80%),　respectively.　Clade　HD　exhibited　high　tolerance　to　starving,　oxygen-limiting　and　high　nitrite　accumulation,　and　thus　became　dominant　Glade　under　insufficient　carbon　sources,　low　DO　and　nitritation　mode.　Clade　IIC　had　a　positive　correlation　with　C/N　ratios,　and　BF　had　a　positive　correlation　with　temperature　(p　＜　0.05).　Shannon　index　under　nitrification　and　nitritation　mode　was　3.54　and　2.38,　respectively.　That　indicated　the　change　of　Accumulibacter　diversities　under　different　operational　conditions.　(C)　2017　Elsevier　B.V.　All　rights　reserved.