In　enhanced　biological　phosphorus　removal　(EBPR)　systems,　seawater　intrusion　may　introduce　uncertainty　into　the　metabolism　of　Polyphosphate　Accumulating　Organisms　(PAOs),　especially　when　volatile　fatty　acid　(VFA)　profiles　derived　from　fermentation　liquids　serves　as　the　carbon　source.　This　study　investigated　the　impacts　of　varying　sea　salt　salinity　levels　on　the　metabolism　of　Accumulibacter　with　different　VFA　as　carbon　sources.　As　sea　salt　salinity　increased　from　0.5　%　to　3.5　%,　catabolism　(phosphorus　release,　glycogen　and　PHA　biodegradation)　was　inhibited　to　a　much　lower　degree　compared　to　anabolism　(phosphorus　uptake,　glycogen　and　PHA　synthesis).　Under　seawater　conditions,　the　intracellular　free　Mg2+　was　partially　excreted,　leading　to　a　subsequent　reduction　in　glycogen　metabolism　and　PHA　synthesis.　The　decrease　in　PHA　synthesis　resulted　in　the　diminished　aerobic　metabolic　activity　and　polyphosphatase　(PPX)　enzyme　activity,　collectively　causing　decreased　phosphorus　uptake.　Moreover,　additional　energy　consumption　was　used　to　alleviate　osmotic　stress,　which　limited　the　energy　used　for　esterase　activity,　translation　activity,　and　phosphorus　and　glycogen　metabolism,　resulting　in　a　decrease　in　growth　activity.　When　using　butyrate　as　a　carbon　source,　Accumulibacter　exhibited　the　highest　metabolic　activity　(49.8　%),　making　it　more　adaptable　to　seawater　conditions.　The　clade　IIF　was　the　dominant　Accumulibacter　in　seawater　conditions　and　could　synthesize　more　PHA　with　butyrate,　isobutyrate　and　valerate　as　a　carbon　source,　respectively,　stabilizing　aerobic　metabolism.　Therefore,　fermentation　liquid　containing　high　concentrations　of　butyrate　and　the　activated　sludge　dominated　by　clade　IIF　have　the　potential　to　enhance　the　stabilization　of　EBPR　systems　in　wastewater　treatment　plants　infiltrated　by　seawater.　©　2023　Elsevier　B.V.