Growth induction in Spirulina platensis under SiO۲ nanoparticles: Function of antioxidant enzymes, phycobiliproteins, and secondary metabolites

In the current study, the effect of different silicon dioxide nanoparticles (SiO۲ 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 SiO۲ NPS concentrations (۰, ۵۰, ۱۰۰, and ۱۵۰ mg L-۱) for two weeks. Results showed that SiO۲ NPs at ۱۰۰ mg L-۱ 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 SiO۲ NP, although their contents were more increased under ۱۰۰ mg L-۱ treatment. Treatment of SiO۲ NP at ۱۵۰ mg L-۱ induced toxicity in the algal growth along with the accumulation of H۲O۲, inhibition of antioxidant enzyme activities, and decline in the content of secondary metabolites. The findings suggest that ۱۰۰ mg L-۱ SiO۲NPs is an optimum concentration for sustainable production of S. platensis, and may act as an elicitor to stimulate antioxidant metabolites for suppressing oxidative injuries.