Mycogenic fabrication of ZnCu, MnCu, and SeMn nanocomposites for algicidal applications

Eutrophication and climate change increasingly contribute to the occurrence of harmful algal blooms (HABs), threatening aquatic ecosystems and water quality. Although metal-based nanomaterials have shown antimicrobial activity, their algicidal potential against HAB-forming microalgae remains poorly explored. Here, we report a biogenic approach for synthesizing hybrid ZnCu, MnCu, and SeMn nanocomposites (NCs) using the cell-free supernatant of Candida sp. and investigate their algicidal activity against the marine microalga Chlorella marina. Physicochemical characterization (XRD, FTIR, TEM, EDX, ζ-potential, and TGA) confirmed the formation of crystalline, thermally stable nanocomposites and good colloidal stability. All NCs inhibited algal growth in a concentration-dependent manner, with 100 mg/L significantly reducing biomass and the contents of carbohydrates, proteins, and chlorophyll. In contrast, lipid and carotenoid levels increased at lower concentrations (12.5 mg/L), suggesting a protective response to nanocomposite-induced stress. NC treatment also markedly enhanced reactive oxygen species (ROS) production and antioxidant-related responses, as indicated by increases in total phenolic content, DPPH radical scavenging activity, and total antioxidant capacity. Scanning electron microscopy revealed severe cellular deformation, membrane disruption, intracellular leakage, and biofilm disintegration. Overall, these findings demonstrate that the cooperative synergistic effects of the hybrid nanocomposites induce oxidative stress and structural damage, leading to effective algal inactivation. The synthesized biogenic nanocomposites show promise algicidal materials for HAB mitigation and could potentially be incorporated into antifouling membranes for water treatment, supporting more environmental management.