Growth induction in Spirulina platensis under SiO2 nanoparticles: Function of antioxidant enzymes, phycobiliproteins, and secondary metabolites

In the current study, the effect of different silicon dioxide nanoparticles (SiO2 NPs) concentrations was investigated on biomass yield, chlorophyll (Chl a) pigment, antioxidant enzymes, and defence metabolites of Spirulina platensis alga. The alga sample was cultured in the Zarrouk medium supplemented with various SiO2 NPS concentrations (0, 50, 100, and 150 mg L-1) for two weeks. Results showed that SiO2 NPs at 100 mg L-1 increased significantly dry weight, specific growth rate, and Chl pigment, possibly due to the induction of protein content and antioxidant enzyme activities of catalase and peroxidase. Secondary metabolites such as phycobiliprotein, phycocyanin, allophycocyanin, phycoerythrin, carotenoids, and extracellular polymeric substances increased upon all concentrations of SiO2 NP, although their contents were more increased under 100 mg L-1 treatment. Treatment of SiO2 NP at 150 mg L-1 induced toxicity in the algal growth along with the accumulation of H2O2, inhibition of antioxidant enzyme activities, and decline in the content of secondary metabolites. The findings suggest that 100 mg L-1 SiO2NPs is an optimum concentration for sustainable production of S. platensis, and may act as an elicitor to stimulate antioxidant metabolites for suppressing oxidative injuries.