Antioxidant Status and CO₂ Biofixation of Chlorella sp. Strain Under Sequential Photoautotrophic Cultivation with Aphotic Induction of Biotechnologically Valuable Compounds Accumulation

Chlorella is a valuable object of biotechnology with high productivity of biomass and metabolites. The use of Chlorella for CO₂ binding in autotrophic metabolism is also discussed. Various types of stress are used to increase the yield of valuable metabolites. One of the effective approaches may be dark stress. However, there is insufficient data to fully understand the effect of dark stress on productivity, biochemical parameters, the antioxidant system, and the rate of CO₂ fixation by Chlorella during the transfer from autotrophic culture to aphotic conditions. To study these processes, we used two-step cultivation. In the second step, the biomass was grown for 96 h on a BBM medium under standard lighting and in aphotic conditions. According to the results of the study, the metabolic systems of the studied strain of Chlorella sp. CAMU G–145 specifically react to cultivation under aphotic conditions. The greatest response was found in lipid–protein metabolism and the antioxidant defense system, which determines an increase in the overall antioxidant status of cells. At the same time, productivity, CO₂ absorption characteristics, and pigment composition of the photosynthetic system did not change after 96 h of darkening. In general, this approach is a promising strategy for increasing biotechnological productions efficiency.