Photogranules　composed　of　algae,　nitrifiers,　and　anammox　bacteria　are　promising　for　nitrogen　removal　from　wastewater　with　reduced　aeration　and　carbon　emissions.　However,　it　is　difficult　to　be　achieved　as　the　potential　inhibition　of　anammox　bacteria　by　light.　In　this　study,　a　syntrophic　algal-partial　nitrification/anammox　granular　sludge　process　was　developed,　with　a　nitrogen　removal　rate　of　294.5　mg　N/(L·d).　We　found　the　symbiosis　in　the　community　promoted　the　adaptation　of　anammox　bacteria　under　light,　and　cross-feeding　played　an　important　role.　Microalgae　in　the　outer　layers　of　photogranules　sheltered　most　of　the　light　and　supplied　cofactors　and　amino　acids　to　promote　nitrogen　removal.　In　particular,　Myxococcota　MYX1　degraded　the　extracellular　proteins　produced　by　microalgae,　providing　amino　acids　to　the　entire　bacterial　community,　which　helped　anammox　bacteria　save　metabolic　energy　and　adapt　to　light.　Notably,　the　anammox　bacteria　Candidatus　Brocadia　exhibited　unique　light-sensing　potential　and　adaptations　to　light　irradiation　compared　with　Candidatus　Jettenia,　including　diverse　DNA　repair,　scavenging　of　reactive　oxygen　species,　cell　movement.　The　phytochrome-like　proteins　encoded　by　Candidatus　Brocadia　further　facilitated　their　spatial　positioning　and　niche　partitioning　in　photogranules.　This　study　provides　insights　into　the　response　of　anammox　bacteria　in　the　algae-bacteria　symbiosis　system　and　suggests　its　potential　application　for　carbon-negative　nitrogen　removal.　©　2023