engleski

Surface Coating-Modulated Phytotoxic Responses of Silver Nanoparticles in Chlorella vulgaris

Silver nanoparticles (AgNPs) attract a great deal of attention due to their antimicrobial effects, for which they are implemented in a wide range of commercial products. However, due to their reactivity and toxicity, they pose a significant risk to aquatic ecosystems. To evaluate the impact of AgNPs on aquatic habitats, Chlorella vulgaris was used as a model organism. To assess the effect of AgNPs on C. vulgaris, algal cultures were grown in liquid BBM nutrient medium for 4 days after which they were exposed to AgNPs coated with citrate or CTAB, and to AgNO3 which was used as ionic Ag control. Concentration endpoints were obtained by growth inhibition test (72 h) and the estimated 25% growth rate inhibition (EC25) values for AgNP-citrate, AgNP-CTAB and AgNO3 were 0.188 mg L-1, 0.895 mg L-1 and 0.130 mg L-1, respectively. After 72h-treatment, the amount of synthesized oxygen, and photosystem II efficiency were analysed to address the impact of AgNPs on the photosynthetic apparatus. Furthermore, reactive oxygen species (ROS) levels and membrane lipid damage were analysed to investigate how well algae cells cope in the presence of AgNPs. To analyse ROS formation, algal suspensions were incubated with fluorogenic dyes (H2DCFDA and DHE) and visualized by a fluorescence microscope. To visualize ultrastructural changes, ultrathin sections of algal cells were analysed by transmission electron microscope (TEM). To further investigate the interaction between AgNPs and algal extracellular polymeric substances (EPS), cells were observed directly by TEM, and by fluorescence microscopy using FITC-labelled lectins. Obtained results indicate a differential effect of differently coated AgNPs on C. vulgaris since a significant reduction in newly synthesized oxygen and PSII efficacy after all treatments compared to the control were observed. Furthermore, differentially increased ROS content after all treatments (Fig. 1), in regard to used coatings, compared to control is suggestive of membrane lipids damage through ROS molecules. TEM analyses showed damaged ultrastructure (Fig. 2) with multiple NPs in EPS of algal cells (Fig. 3), while fluorescence microscopy showed increased EPS synthesis after all treatments, especially after AgNPs-CTAB, which could alleviate AgNPs toxic effect (Fig. 4). In conclusion, all forms of silver (AgNP-citrate, AgNP-CTAB and AgNO3) showed an adverse and detrimental effect primarily on the photosynthetic apparatus and membrane lipids mostly through increased synthesis of ROS molecules, where AgNP-citrate had most damaging effect. Due to the treatment with NPs, the synthesis of EPS increases, especially after AgNP- CTAB treatment, which can maintain and consequently reduce the harmful effect of AgNPs on the cells themselves.

Chlorella vulgaris ; ultrastructure ; silver nanoparticles

nije evidentirano