Beneficial impact of AgNPs on fucoxanthin production and evaluation of phytochemical variations in Isochrysis sp.

Silver nanoparticles (AgNPs) are commonly transformed into various engineered nanomaterials for various applications, leading to their unavoidable disposal in the environment. Despite their toxicity, knowledge gaps remain regarding the metabolic perturbations induced by AgNPs on phytoplankton, which play a crucial role in global biogeochemical cycles and food-web dynamics. This study aimed to utilize AgNPs to elicit stress response of Isochrysis sp. KRJ-105, for enhancing fucoxanthin production, a valuable pigment with anti-inflammatory and antioxidant properties. The microalgae were treated with different AgNP concentrations (10, 30, 50, 70, and 100 mg/L) for 12 days, and the results showed that the addition of 50 mg/L AgNPs significantly promoted cellular fucoxanthin biosynthesis (34.61 ± 0.50 mg/g), a 5.94 mg/g higher production compared to the control (28.67 ± 1.01 mg/g). This study represents the first-time report of higher fucoxanthin production in Isochrysis sp. compared to previous reports in the last decade. Furthermore, AgNPs induced stress conditions in Isochrysis sp., also reflected in growth rates and alterations in biochemical composition, including total carbohydrate, total protein, lipid, carotenoid, and reactive oxygen species (ROS) content. Scanning electron microscopy (SEM) and Energy-dispersive X-ray (EDAX) analysis revealed the interaction of AgNPs with the cell surface of Isochrysis sp. KRJ-105. These findings provide novel insights into microalgal interactions with nanoparticles, offering fundamental knowledge on physiochemical changes induced in Isochrysis sp., and its future development in cultivation aspects for superior commercial fucoxanthin production.