Cytotoxic effects of zinc oxide nanoparticles on cyanobacteriumSpirulina (Arthrospira) platensis

Abstract

BackgroundThe extensive usage of zinc oxide nanoparticles (ZnO NPs) in industrial and consumer products raises the risk of releasing their residues into the aquatic environment. The presence of ZnO NPs in the aquatic environment could potentially cause cytotoxic effects on aquatic organisms. Thus, investigating the cytotoxic effects of ZnO NPs on microalgae, which form the base for the food web of aquatic biota, is essential to gain information regarding the ecotoxicological effects of metallic oxide nanoparticles in the aquatic ecosystem. Therefore, the present study has investigated in detail the assorted cytotoxic effects of ZnO NPs on S. platensis using various concentrations of ZnO NPs (10–200 mg/L) from 6 to 96 h to explore the dose- and time-dependent cytotoxic effects.MethodsThe cytotoxic effects were all assessed through quantification of loss in cell viability, reduction in biomass and decrease in photosynthetic pigments such as chlorophyll-a, carotenoids and phycocyanin. The surface interactions of nanoparticles and the subsequent morphological alterations on algal cells were examined by optical and scanning electron microscopy (SEM). The intracellular alterations of algal cells were studied using transmission electron microscopy. Furthermore, Fourier transformed infrared (FTIR) spectrum was obtained to investigate the involvement of algal surface biomolecules in surface binding of ZnO NPs on algal cells.ResultsThe treatment of ZnO NPs on S. platensis exhibited a typical concentration- and time-dependent cytotoxicity. Results showed a significant (p < 0.05) cytotoxicity from 24 h onwards for all tested concentrations of ZnO NPs. The maximum cytotoxicity on algal cells was achieved at 96 h of exposure to ZnO NPs. In comparison with control, the algal cells that interacted with 200 mg/L of ZnO NPs for 96 h showed 87.3 ± 1% loss in cell viability, 76.1 ± 1.7% reduction in algal biomass, 92.5 ± 2.2%, 76.2 ± 2.2% and 74.1 ± 3.4% decrease in chlorophyll-a, carotenoids and phycocyanin contents respectively. Our study confirmed the cytotoxicity of ZnO NPs through the algal growth inhibition with 72 h EC10 and EC50 values of 1.29 and 31.56 mg/L, respectively. The microscopic examinations of the algal cells that interacted with ZnO NPs showed severe cell membrane and intracellular damage. The SEM EDX spectrum of ZnO NPs treated algal biomass evidenced the surface accumulation of zinc in the biomass. Finally, the FTIR spectrum confirmed the involvement of amino, hydroxyl and carboxylic groups of algal cell wall in the surface interaction of ZnO NPs on the algal cells.DiscussionThe results showed that the treatment of ZnO NPs on S. platensis triggered substantial cytotoxicity and caused cell death. Hence, S. platensis could be potentially used as a bioindicator for testing toxicity of ZnO NPs in aquatic environment.

Cellular accumulation and cytotoxic effects of zinc oxide nanoparticles in microalga Haematococcus pluvialis

“…2C and 2D). Similar results were reported by Dmytryk, Saeid & Chojnacka (2014), Zinicovscaia et al (2016), and Djearamane et al (2018) who demonstrated the cellular accumulation of selenium, zinc and ZnO NPs in the algal biomass of Spirulina platensis through EDX analysis. Furthermore, the quantification of ZnO NPs accumulated in algal cells using ICP OES exhibited a dose- and time-dependent increase in cellular accumulation of ZnO NPs in H. pluvialis with highest zinc accumulation of 6.27–18.36 pg/cell (Fig.…”

“…The cytotoxicity parameters of the present study evidently demonstrated a characteristic dose- and time-dependent loss in cell viability and a decrease in algal biomass which confirmed the growth inhibitory effect of ZnO NPs on H. pluvialis . A similar trend was observed with the study conducted on freshwater microalga Chlorella vulgaris (Suman, Rajasree & Kirubagaran, 2015) and the marine microalga S. platensis (Djearamane et al, 2018). However, the present study results reported lower sensitivity of H. pluvialis towards ZnO NPs toxicity in comparing with S. platensis and C. vulgaris .…”

“…Similarly, the algal growth inhibition results from the penetration of NPs into the cell envelope and the following disruption in cell membranes causing cell membrane rupture and leakage of intracellular contents (Chen et al, 2012). The surface binding and the consequent accumulation of nanosized particles on the algal cell surface compromise the cell membrane integrity and cell morphology, and eventually resulting in cell death due to the mechanical damage (Djearamane et al, 2018) or by the intracellular dissociation of metal ions from the internalized NPs that disturbs cellular metabolism (Lin & Xing, 2008). Further, the entrapment of large aggregates of NPs on algal cells reduces the light availability to algal cells (Hazeem et al, 2016) and also the adsorption of nutrients by NPs impairs the availability of nutrients to algal cells, ultimately resulting in growth inhibition (Tang et al, 2013).…”

“…Hence, it is essential to investigate the impact of ZnO NPs on the environment, especially on the aquatic organisms. Previous studies revealed the potential of microalgae as model organisms for the toxicity study of metallic oxide NPs in the environment (Franklin et al, 2007; Griffitt et al, 2008; Navarro et al, 2008; Battin et al, 2009; Manzo et al, 2013; Djearamane et al, 2018). Microalgae have been used as a bio-indicator for freshwater pollutants due to their high bioaccumulation capabilities (Barhoumi & Dewez, 2013) and the ability to indicate the amount of pollutants in water through the changes in algal biomass and photosynthetic pigments (Zhou et al, 2014).…”

Green Synthesis of Zinc Oxide Nanoparticles (ZnO-NPs) Using Arthrospira platensis (Class: Cyanophyceae) and Evaluation of their Biomedical Activities

“…EA03 [ 50 ]. In addition, Djearamane et al [ 51 ] reported that the main components of ZnO-NPs synthesized by Spirulina platensis were Zn and O.…”