Investigating nanoparticle formation and the metabolic response of Ulva prolifera to gold ions

Abstract

With the application of AuNPs in cancer treatment and targeted drug delivery, algae have been proposed as potential eco-friendly nanofactories for the synthesis of AuNPs. Unfortunately, little is known about how HAuCl4 is converted to AuNPs, and the toxicity of HAuCl4 affects the mechanisms underlying metabolite shifts in algae. The aim of this work is to systematically study the cellular metabolism profile of the green alga Ulva prolifera upon exposure to HAuCl4 by using metabolomics based on nontargeted liquid chromatography and mass spectrometry. The results showed that the metabolite profiles of UpAu (treatment) and UpC (control) were clearly separated, as revealed by PCA and PLS-DA. A total of 200 metabolites and 16 specific metabolic pathways were significantly altered by exposure to HAuCl4, many of which are associated with the cellular stress response and AuNP synthesis. Importantly, the expression levels of crotonobetaine, ascorbic acid, jasmonic acid, ubiquinol, and vitamin D3 involve in stress-related metabolites increased, and those of secondary metabolites such as diosgenin and hecogenin terpendole G, and steroids, as reducers, were also all significantly increased. In addition, the downregulated metabolites included linoleic acid, stearidonic acid and arachidonic acid, which affect membrane composition and stability. Importantly, a metabolic analysis identified some novel metabolic pathways that are specifically regulated by HAuCl4, including linoleic acid metabolism, arachidonic acid metabolism, porphyrin and chlorophyll metabolism, steroid biosynthesis, and biosynthesis of secondary metabolites regulated by HAuCl4. In summary, the manifestation of differential metabolic profiles combined with SEM analysis of exposure to HAuCl4 provided evidence of damage to photosynthesis and membranes. These results provide holistic information about complex disturbances in the metabolite profiles of U. prolifera exposed to HAuCl4 and provide new insights into the mechanisms of HAuCl4 toxicity and AuNP synthesis in macroalgae.