| Summary: | In the present contribution, the differentiation in the molecular structure and function of the photosynthetic apparatus of the unicellular green alga <i>Chlorella vulgaris</i> was studied at several light intensities (0–400 μmol m<sup>−2</sup> s<sup>−1</sup>) and various CO<sub>2</sub> concentrations (0.04–60% CO<sub>2</sub>), in completely autotrophic conditions. Asymmetries that occur by different light intensities and CO<sub>2</sub> concentrations induce metabolic and functional changes. Using chlorophyll fluorescence induction techniques (OJIP test), we showed that <i>Chlorella vulgaris</i> tolerates extremely high CO<sub>2</sub> levels and converts them photosynthetically into valuable products, including O<sub>2</sub> and biomass rich in carbohydrates and lipids. Interestingly, the microalga <i>Chlorella vulgaris</i> under extremely high CO<sub>2</sub> concentrations induces a new metabolic state intensifying its photosynthetic activity. This leads to a new functional symmetry. The results highlight a potent CO<sub>2</sub> bio-fixation mechanism of <i>Chlorella vulgaris</i> that captures up to 288 L CO<sub>2</sub> L PCV<sup>−1</sup> day<sup>−1</sup> under optimal conditions, therefore, this microalga can be used for direct biological CO<sub>2</sub>-reducing strategies and other green biotechnological applications. All of the above suggest that <i>Chlorella vulgaris</i> is one of the most prominent competitors for a closed algae-powered bioreactor that is able to consume huge amounts of CO<sub>2</sub>. Thus, it is a sustainable and natural bioenergetic system with perspectives in dealing with major environmental issues such as global warming. In addition, <i>Chlorella vulgaris</i> cultures could also be used as bioregeneration systems in extraterrestrial missions for continuous atmospheric recycling of the human settlements, paving the way for astrobiological applications.
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