Impact of silver nanoparticles on the growth, fatty acid profile, and antioxidative response of Nannochloropsis oculata

Key message AgNPs caused significant toxicity and induced oxidative stress in the microalga N. oculata. Also, the interaction between AgNPs and algae led to cell membrane damage. Silver nanoparticles (AgNPs) have been broadly applied in several industrial sectors, and thus inevitably released into the aquatic environments. In the present study, the effect of various concentrations of AgNPs (up to 50 mg/L) on the microalga Nannochloropsis oculata ( N. oculata ) was investigated. The obtained results showed that half maximal effective concentration (EC 50 ) of AgNPs for the microalga was 20.88 mg/L. Also, the different applied concentrations of AgNPs inhibited the cell growth as well as the photosynthetic machinery and stimulated the production of malondialdehyde (MDA) and hydrogen peroxide (H 2 O 2 ). AgNP treatments dramatically enhanced the content of carotenoids in the treated algae, while they significantly reduced the quantity of phenolic compounds. Furthermore, AgNPs increased the enzymatic activity of catalase (CAT), ascorbate peroxidase (APX) and lactate dehydrogenase (LDH), while they considerably decreased the activity of polyphenol oxidase (PPO) compared to the control sample. Gas chromatography–mass spectrometry (GC–MS) examination demonstrated that after exposure of N. oculata cells to AgNPs, the amounts of saturated fatty acids (SFAs) and polyunsaturated fatty acids (PUFAs) were raised, while the levels of monounsaturated fatty acids (MUFAs) were lessened. The Fourier transform infrared spectroscopy (FTIR) results and the microscopic images revealed the interaction of AgNPs with the cells of N. oculata .