Modeling the dynamics of pigment content in cells of Dunaliella salina Teod. unicellular alga at the stage of carotenogenesis

The work is focused on modeling of chlorophyll and carotenoids content dynamics in the in cells of the unicellular algae D. salina, living in salt water, at carotenogenesis induction phase. A mathematical model of pigments content in microalgae cells, which experience excess of light energy and the limit of nutrient medium mineral components, is proposed. The model is based on assumption, that observed rate of variation in pigment concentration is an algebraic sum of the rates of synthesis, photodestruction and partial recovery of photo-oxidized pigments. The rate of secondary carotenoids synthesis does not depend on external conditions and is determined by the quantity of key enzyme complex and its turnover rate. The rate of secondary carotenoids and chlorophyll photodestruction depends on the effective light intensity and is proportional to the amount of absorbed photosynthetically active radiation energy. The verification of the derived equations was conducted in the course of D. salina cultivation at the carotenogenesis stage. The specific rate of chlorophyll a photodestruction was determined, which resulted in 0.12 days$^{-1}$. The secondary carotenoids concentration increases up to the maximum value, which is determined by the ratio of synthesis and photodestruction specific rates, as well as the maximum culture density. Under conditions of natural light in the Sevastopol region, the maximum concentration of carotenoids was 18.33 mg/l or 0.73 g/m$^2$.