Metabolomics responses of Microcystis aeruginosa to UV-B radiation and TiO₂ nanoparticles in monoculture and co-culture with Lemna minor

As anthropogenic activities have increased, stratospheric depletion has also increased, resulting in intensified ultraviolet (UV) radiation, especially UV-B, reaching the Earth's surface. Concurrently, the expansion of the manufacturing sector has increased the release of titanium dioxide nanoparticles (TiO₂ NPs) into freshwater ecosystems. Both UV-B radiation and TiO₂ NPs are known to increase reactive oxygen species (ROS) production; however, their combined effects on the metabolomic profile of cyanobacteria during interactions with aquatic macrophytes, remain poorly understood. This study investigated the effects of high (2 W m −2 ) and low (0.8 W m −2 ) UV-B radiation, individually and in combination with TiO₂ nanoparticles (48 mg/L), on the growth and metabolomic profile of Microcystis aeruginosa in monoculture and co-culture with Lemna minor . The experiment was conducted for seven days under laboratory conditions designed to simulate acute stress, and growth was monitored on days 1, 3, 5, and 7. Metabolomic profiling was performed using two-dimensional gas chromatography coupled with time-of-flight mass spectrometry (GC × GC-TOFMS). The results showed that the growth of Microcystis aeruginosa was significantly reduced across all treatments but not in the co-culture experiment, revealing the regulatory role of biological interactions. Metabolomic analysis revealed treatment-specific changes in amino acid, lipid, organic acid, carbohydrate, and secondary metabolic pathways under UV-B and TiO₂ NPs exposure, highlighting oxidative stress and defense mechanisms. The findings show that abiotic and biotic stressors interact to redefine metabolic pathways and oxidative stress responses in Microcystis aeruginosa , highlighting the importance of macrophyte interactions and chemical stressors in predicting bloom formation in freshwater ecosystems.