Mechanistic insights into light-driven self-regulation of microbial interactions and metabolic shifts in autotrophic...

Light intensity regulates energy input and ecological balance in algal-bacterial symbiotic systems; however, underlying light-driven mechanisms remain unclear. This study explored microbial community succession, functional shifts, and metabolic regulation under light gradients in an algal-bacterial symbiotic system comprising microalgae, partial-nitrification, and anaerobic ammonium oxidation. Light intensity exhibited a dual effect. Optimal total nitrogen removal efficiency (TNRE) reached 91% at a light intensity of 280 ± 10 μmol/(m²·s), reflecting balanced algal-bacterial interactions. Higher light (380 ± 10 μmol/(m²·s)) induced excessive oxygen production and nitrite accumulation, thereby reducing TNRE to 76%. Ultra-high light (480 ± 10 μmol/(m²·s)) triggered algal photoinhibition, decreasing oxygen production and restoring TNRE to 88%. Microbial network stability declined with increasing light intensity but recovered under ultra-high light. Meanwhile, metabolism shifted significantly from purine and nucleotide metabolism to tryptophan metabolism (p < 0.05), reflecting a metabolic transition from proliferative growth to stress resistance. These findings demonstrate the intrinsic light-driven self-regulatory mechanism in autotrophic algal-bacterial systems.