Performance and mechanism of phosphorus transformation in the microalgal-bacteria symbiotic system under varying...

Light intensity (LI) critically regulates phosphorus (P) uptake and fixation during microalgae photosynthesis, but how LI impacts P transformation and key microbial taxa succession in the microalgal-bacteria symbiotic system (MBSS) remains unclear. This study demonstrates that optimal P removal (>92.5% phosphate elimination) occurs at 80-120 μmol photons m^-2 s^-1, with the dominant particulate phosphate fraction and significantly reduced dissolved P fractions. At low LI (<20 μmol photons m^-2 s^-1), polyphosphate accumulation was primarily mediated by microalgae, as weak light suppressed polyphosphate-accumulating organisms (PAOs). In contrast, high LI shifted the dominance to PAOs (relative abundance > 11%), which collaborated with microalgae that provided photosynthetic energy and oxygen, while PAOs facilitated P uptake, polyphosphate accumulation, and organic P mineralization. High LI further promoted recalcitrant organophosphates accumulation, potentially reducing dissolved organic P bioavailability and eutrophication risk, thereby improving long-term P removal stability. These findings reveal that LI regulates P removal by steering microbial community assembly, functional gene expression, and molecular P speciation, offering theoretical insights for advanced wastewater treatment.