The Effect of Copper and Selenium Nanocarboxylates on Biomass Accumulation and Photosynthetic Energy Transduction Efficiency of the Green Algae Chlorella Vulgaris

Abstract

Nanoaquachelates, the nanoparticles with the molecules of water and/or carboxylic acids as ligands, are used in many fields of biotechnology. Ultra-pure nanocarboxylates of microelements are the materials of spatial perspective. In the present work, the effects of copper and selenium nanoaquachelates carboxylated with citric acid on biomass accumulation of the green algae Chlorella vulgaris were examined. Besides, the efficiency of the reactions of the light stage of photosynthesis was estimated by measuring chlorophyll a fluorescence. The addition of 0.67–4 mg L ⁻¹ of Cu nanocarboxylates resulted in the increase in Chlorella biomass by ca. 20%; however, their concentrations ranging from 20 to 40 mg L ⁻¹ strongly inhibited algal growth after the 12th day of cultivation. Se nanocarboxylates at 0.4–4 mg L ⁻¹ concentrations also stimulated the growth of C. vulgaris, and the increase in biomass came up to 40–45%. The addition of Se nanocarboxylates at smaller concentrations (0.07 or 0.2 mg L ⁻¹) at first caused the retardation of culture growth, but that effect disappeared after 18–24 days of cultivation. The addition of 2–4 mg L ⁻¹ of Cu nanocarboxylates or 0.4–4 mg L ⁻¹ of Se nanocarboxylates caused the evident initial increase in such chlorophyll a fluorescence parameters as maximal quantum yield of photosystem II photochemistry ( F _v/ F _m) and the quantum yield of photosystem II photochemistry in the light-adapted state ( F _v'/ F _m'). Photochemical fluorescence quenching coefficients declined after 24 days of growth with Cu nanocarboxylates, but they increased after 6 days of the addition of 2 or 4 mg L ⁻¹ Se nanocarboxylates. Those alterations affected the overall quantum yield of the photosynthetic electron transport in photosystem II.