A new subarctic strain of Tetradesmus obliquus. Part II: comparative studies of CO2-stress toleranceстатья
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Аннотация: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 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 of the cultural medium; (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). N starvation enhances the effects of high-CO2 stress in CO2-intolerant
microalga. The results of this work are discussed in the context of selection of tolerant
algal strains for CO2 biomitigation applications.