In recent years, cyanobacteria were found to be important sources of previously known bioactive substances, as well as newly discovered secondary metabolites. In this research, one of the strains – Calothrix marchica Lemmermann CNMN-CB-18 — was isolated in pure culture and characterized. This strain grows in the soil of the Cogâlnic River meadow, Cimislia, Moldova. The two step cultivation of C. marchica with switching of the illumination from 1500 to 2500 lx on the 7th day lead to a higher carbohydrate content (up to 40.5%) on BG11 medium when compared to its growth in different lighting regimes (36.5–37.5%). The productivity of the strain showed similar tendencies: it reached values of up to 1.314 g/L for the two-step cultivation, whereas the 1500 and 2500 lx continuous illumination displayed lower values — 0.714 and 0.87 g/L, respectively. The same trends were attested for growth on Drew medium, however its poorer content of minerals lead to lower yields as compared to BG11. The biochemical analysis of C. marchica grown on Drew medium demonstrates rich amounts of lipids — 33.7%, and carbohydrates — 32.9%, followed by proteins with 14.7%. Due to its ability to adjust to various growth conditions under controlled cultivation for the accumulation of high amounts of carbohydrates, this strain is a valuable source of bioactive substances for use in biotechnology in order to be applied in diverse fields such as: cosmetics, pharmaceuticals, agriculture, etc.
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