INDUCTION OF CAROTENOGENESIS IN Desmodesmus armatus (Chod.) Hegew CULTIVATED ON THE WASTE WATER FROM RECIRCULATING AQUACULTURE SYSTEM
Authors: M. M. Marchenko, I. V. Dorosh, L. M. Cheban
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The aim of the study was to develop the biotechnology approach for obtaining secondary carotenoids of green microalgae Desmodesmus armatus (Chod.) Hegew. under conditions of two-stage cultivation on waste water from recirculating aquaculture system in response to the action of inducers of different origin. By chemical nature, secondary carotenoids are C40-ketocarotinoids - intermediates of enzymatic oxidation of β-carotene to astaxanthin.
The study presents the conditions for cultivation of D. armatus on the waste water from the recirculating aquaculture system by a two-stage accumulation process, where conditions for rapid growth of biomass were created at the first stage, and the biosynthesis of the target product was induced by the introduction of carotenoid biosynthesis precursors (C6H12O6, CH3COONa), promoters of free radical oxidation (FeSO4 / H2O2) or osmotic stress (NaCl) into the nutrient medium. It was shown that the first phase of cultivation was characterized by high growth and productive indices: the amount of biomass was up to 13 g/l, the content of total proteins was 37.9 %, lipids – 26 % and total carotenoids – 7.5 % per gram of dry biomass. Among carotenoids, the presence of zeaxanthin, lutein, β-carotene, insignificant amounts of astaxanthin, canthaxanthin, esters of adonixanthin and astaxanthin were detected. The features of the adaptive response of D. armatus to the influence of factors that induce secondary carotenogenesis are established. Among them is retention of the number of cells or doubling of their number during the use of chemical activators. Decrease in the activity of cytochrome oxidase as an indicator of the metabolic activity of the culture.
Thus, the possibility of increasing the content of β-carotene and astaxanthin in D. armatus biomass, essential for fish and crustaceans, by introducing promoters of free radical oxidation and osmotic stress NaCl (200 mM) or Fe2+ (200 mM) and H2O2 (10–4 mM) into the waste water from RAS in the second phase of cultivation was established. Metabolic disbalance in D. armatus cells, which were observed under the influence of chemical factors, led to a redistribution of the main nutrients profile. Biosynthesis and accumulation of lipids were activated against the background of intensive carotenogenesis.