New insights into light-dependent pathways and mechanisms of phosphorus removal in hypersaline microalgae-bacteria...

Hypersaline microalgae-bacteria system (HMBS) offers a sustainable strategy for nutrient remediation from saline wastewater, but the coupling mechanisms between phosphorus removal pathways and light regulation remain elusive. Herein, we interrogated the phosphorus removal dynamics and underlying mechanisms in HMBS under varying light intensities (2,000, 10,000, and 20,000 lux). The results demonstrated that phosphorus removal was optimized at moderate light intensity (10,000 lux), surpassing those at low and high light intensities by 15.3% and 38.3%, respectively. Mass balance analysis revealed that biologically induced phosphate precipitation (BIPP), rather than biological assimilation, constituted the main phosphorus sink. Mechanistically, moderate light maintained redox homeostasis and facilitated the enrichment of keystone taxon Paracoccus, which drove a robust metabolic cycle of light-phase phosphate uptake and dark-phase release. The latter created a localized supersaturated microenvironment, providing the thermodynamic driving force for BIPP. Concurrently, moderate light stimulated the secretion of extracellular proteins (PN) rich in β-sheet structures, which served as superior nucleation templates to accelerate biomineralization. Conversely, high light intensity triggered severe oxidative stress via photo-inhibition, which disrupted Paracoccus-mediated phosphorus cycle and increased random coils in PN, thereby suppressing BIPP. This study could advance the understanding of phosphorus removal mechanisms in HMBS with a novel light-regulated, biomineralization-dominant pathway.