Directed cultivation of Chlorella sorokiniana to increase carotenoid synthesis

Abstract

Chlorella sorokiniana is a promising species for cultivation both in the laboratory cultivator and on an industrial scale. Its biomass is the source of many valuable components, including plastid pigments, which have high antioxidant activity. The metabolism of Chlorella sorokiniana is subject to change under the influence of various cultivation conditions. With dosed ultraviolet radiation, a compensatory increase in the synthesis of carotenoids is possible, which prevents oxidative stress. The cultivation of C. sorokiniana (strain 211-8k) was carried out in various conditions of illumination: the control version – illumination with a fluorescent lamp; option 1 – dosed periodic ultraviolet exposure every day for 15 min (spectral region of the light flux 280-315 nm (UV-B), intensity 1300 Lux) and further illumination with a fluorescent light; option 2 – ultraviolet irradiation for 30 min (spectral region of the light flux 280-315 nm (UV-B), intensity 1300 Lux) in the stabilization phase. Periodic ultraviolet irradiation negatively affects the growth of C. sorokiniana population, which manifests itself only on the 9th day, the biomass yield is significantly reduced. A single UV exposure for 30 minutes leads to a slight decrease in the yield of air-dried biomass, which can be compensated with a further increase in population. Periodic ultraviolet exposure leads to an increase in the synthesis of carotenoids, the yield in terms of dry biomass exceeds the control sample by an average of 30%. A single ultraviolet irradiation for 30 minutes in the stabilization phase leads to a decrease in the content of both chlorophyll and carotenoids in the biomass. Microscopic examination of microalgae populations showed that ultraviolet exposure leads to the appearance of cells with signs of apoptosis: large cells with large vacuoles, a condensed nucleus, and bleached chloroplast. A further direction of the study is the selection of conditions allowing to increase the yield of carotenoids with minimal loss of microalgae biomass.