The Microalga Chlorella vulgaris as a Natural Bioenergetic System for Effective CO2 Mitigation—New Perspectives against Global Warming

Fanourios Mountourakis,Kiriakos Kotzabasis,Aikaterini Papazi

doi:10.3390/sym13060997

Abstract

In the present contribution, the differentiation in the molecular structure and function of the photosynthetic apparatus of the unicellular green alga Chlorella vulgaris was studied at several light intensities (0–400 μmol m−2 s−1) and various CO2 concentrations (0.04–60% CO2), in completely autotrophic conditions. Asymmetries that occur by different light intensities and CO2 concentrations induce metabolic and functional changes. Using chlorophyll fluorescence induction techniques (OJIP test), we showed that Chlorella vulgaris tolerates extremely high CO2 levels and converts them photosynthetically into valuable products, including O2 and biomass rich in carbohydrates and lipids. Interestingly, the microalga Chlorella vulgaris under extremely high CO2 concentrations induces a new metabolic state intensifying its photosynthetic activity. This leads to a new functional symmetry. The results highlight a potent CO2 bio-fixation mechanism of Chlorella vulgaris that captures up to 288 L CO2 L PCV−1 day−1 under optimal conditions, therefore, this microalga can be used for direct biological CO2-reducing strategies and other green biotechnological applications. All of the above suggest that Chlorella vulgaris is one of the most prominent competitors for a closed algae-powered bioreactor that is able to consume huge amounts of CO2. Thus, it is a sustainable and natural bioenergetic system with perspectives in dealing with major environmental issues such as global warming. In addition, Chlorella vulgaris 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.

Highlights

Over the last couple of centuries, industrialization along with urbanization have brought an immense increase in greenhouse gases (GHGs), mostly carbon dioxide (CO2 ), which is considered one of the main causes of global warming [1] and other major environmental problems, such as ocean acidification [2]
The results reveal that stress was induced by increasing the light intensity under ambient CO2 concentration in closed cultivation systems
The present study examined the metabolic and functional differentiation of the green alga Chlorella vulgaris under various light intensities and extreme CO2 concentrations

Summary

Introduction

Over the last couple of centuries, industrialization along with urbanization have brought an immense increase in greenhouse gases (GHGs), mostly carbon dioxide (CO2 ), which is considered one of the main causes of global warming [1] and other major environmental problems, such as ocean acidification [2]. Atmospheric CO2 concentration increased rapidly from 280 ppm in 1850 [3] to more than 417 ppm in 2021, with more than half of this increase happening in the last 30 years [4]. Human activities release about 35 gigatons of CO2 every year, as opposed to almost 10 megatons 2 centuries ago [6]. There is already clear evidence that anthropogenic emissions of GHGs, such as CO2 , alter the natural carbon cycle, which leads to an accelerated warming of our planet [7].

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Conclusion