NANOSELENIUM REGULATED GROWTH AND LIPID PRODUCTION OF Dunaliella tertiolecta- INCREASING MICROALGAL POTENTIAL FOR BIOFUEL PRODUCTION

In the continuous search for renewable, environmentally friendly and commercially feasible alternative to fossil fuels microalgae are drawing attention as feedstock of high potential for biofuel production. In addition to high lipid content and a simple production, advantage of microalgae is possibility to amplify lipid production under stress conditions. Recently, application of selenium, an essential micronutrient, as a stressor received increased attention since exposure of microalgae to Se lead to increase in the content of not only lipids, but antioxidant enzymes and photosynthetic pigments as well. However, Se also exhibits toxicity, depending on its dose and chemical form. Recent studies have shown that this drawback can be surpassed by using nanoselenium. The aim of this study was to determine the influence of different dose of nanoselenium on the growth and lipid content of Dunaliella tertiolecta which is considered to be a promising feedstock for biofuel production since it is fast-growing strain with high-lipid content.

Selenium nanoparticles (Se NPs) were synthetized by mixing sodium selenite and ascorbic acid solutions and characterized by dynamic light scattering. D. tertiolecta was exposed to 0.01-50 mg L^-1 of selenium in the form of Se NPs under optimal culture conditions (F2 medium, 25 ± 2 °C, constant illumination of 8,000 lux, pH = 6.8). Algal growth inhibition was determined at 24, 48 and 72 h of exposure using hemocytometer. Lipid oxidation was determined after 72 h and lipid content after 14 days.

Algal growth was inhibited by SeNPs in a concentration- and time-dependent manner. After 72 h of exposure a statistically significant decrease of cell concetration was observed at 0.05 mg L^-1 of SeNPs. The highest lipid accumulation was obtained in cultivation at 10 mg L^-1 of SeNPs. After 72 h of exposure SeNPs induced exogenous oxidative stress and were an effective factor for neutral lipid induction in D. tertiolecta (Fig. 1.). Fatty acid composition of SeNPs-treated microorganisms was used for the qualitative analysis of fatty acid as methyl esters. Fatty acids that were most commonly represented in all samples were oleic acid 18:1 (n-9) and eicosenoic acid 20:1 (n-9).

The obtained results point that Se NPs can be an effective inducer of lipid production, which increases biotechnological potential of D. tertiolecta in biofuel production. This approach also opens a way to increase D. tertiolecta potential for other applications.