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A new subarctic strain of Tetradesmus obliquus. Part II: comparative studies of CO2-stress tolerance
- Scherbakov, P., Ismagulova, T., Chernov, T., Gorelova, O., Selyakh, I., Semenova, L., Baulina, O., Chivkunova, O., Lobakova, E., Solovchenko, A.
- Journal of applied phycology 2018 v.30 no.5 pp. 2751-2761
- Desmodesmus, Tetradesmus, air, carbon dioxide, chlorophyll, homeostasis, lipid bodies, lipids, microalgae, nitrogen, pH, phenotype, photosynthesis, physiological response, starch granules, transmission electron microscopy
- A huge interest in CO₂-tolerant microalgae is fueled by development of CO₂-biomitigation methods based on intensive cultivation of microalgae. Still, the mechanisms of CO₂-tolerance are scarcely investigated. Previously, we described a symbiotic Desmodesmus sp. IPPAS S-2014 from a White Sea hydroid tolerant to extremely high (20–100%) CO₂ levels. In the present work, we compared its ultrastructural and physiological responses to those of a novel free-living White Sea strain of Tetradesmus obliquus IPPAS S-2023 characterized in the companion paper. The strain S-2023 is closely related to Desmodesmus sp. IPPAS S-2014 but lacks its tolerance to extremely high CO₂ (it is unable to survive at 100% CO₂ and exhibits a reduced-growth phenotype when sparged with 20% CO₂: air mixture). We compared the responses of the cell organization and photosynthetic activity to 20% CO₂ in the tolerant and the intolerant White Sea chlorophytes using chlorophyll fluorescence measurements and ultrastructural analysis (transmission electron microscopy). The features peculiar to the CO₂-intolerant chlorophyte include (i) inability to maintain pH homeostasis, (ii) a steady decline in the photosynthetic activity of the cells, (iii) a reduction of the photosynthetic membranes, and (iv) delayed accumulation of starch (starch grains) and its subsequent conversion to reserve lipids (oil bodies). Nitrogen starvation enhances the effects of high-CO₂ stress in the CO₂-intolerant microalga. The results of this work are discussed in the context of selection of tolerant algal strains for CO₂ biomitigation applications.