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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.