Directed cultivation of Chlorella sorokiniana for the increase in carotenoids’ synthesis

Abstract

The metabolism of Chlorella sorokiniana is subjected to changes caused by various cultivation conditions. If dosed ultraviolet radiation is used, there is a possibility of a compensatory increase in the synthesis of carotenoids which prevent oxidative stress. Strain 211-8k was cultured under various lighting conditions: control sample was subjected to fluorescent light; sample 1 was subjected to dosed periodic ultraviolet irradiation for 15 minutes every day and fluorescent lighting; sample 2 was subjected to ultraviolet irradiation for 30 minutes in the stabilization phase. Periodic UV exposure negatively affects the population growth of C. sorokiniana which was possible to detect only on the ninth day and the biomass yield significantly decreased. A single UV exposure for 30 minutes lead to a slight decrease in the yield of air-dry biomass which with a further population growth may be compensated. Periodic exposure to UV radiation stimulates carotenoids synthesis, the yield in terms of dry biomass exceeded the control sample on average by 30%. A single ultraviolet irradiation for 30 minutes in the stabilization phase lead to a decrease in the biomass content of both chlorophyll and carotenoids. Microscopy of microalgae showed that ultraviolet radiation leads to the formation of cells with signs of apoptosis.