Abstract
The thermoacidophilic red alga Galdieria sulphuraria has been optimizing a photosynthetic system for low-light conditions over billions of years, thriving in hot and acidic endolithic habitats. The growth of G. sulphuraria in the laboratory is very much dependent on light and substrate supply. Here, higher cell densities in G. sulphuraria under high-light conditions were obtained, although reductions in photosynthetic pigments were observed, which indicated this alga might be able to relieve the effects caused by photoinhibition. We further describe an extensive untargeted metabolomics study to reveal metabolic changes in autotrophic and mixotrophic G. sulphuraria grown under high and low light intensities. The up-modulation of bilayer lipids, that help generate better-ordered lipid domains (e.g., ergosterol) and keep optimal membrane thickness and fluidity, were observed under high-light exposure. Moreover, high-light conditions induced changes in amino acids, amines, and amide metabolism. Compared with the autotrophic algae, higher accumulations of osmoprotectant sugars and sugar alcohols were recorded in the mixotrophic G. sulphuraria. This response can be interpreted as a measure to cope with stress due to the high concentration of organic carbon sources. Our results indicate how G. sulphuraria can modulate its metabolome to maintain energetic balance and minimize harmful effects under changing environments.
Highlights
Specialized microorganisms that populate harsh environments characterized by extreme temperature, pH, and salinity, are called extremophiles [1]
The high-light intensity led to growth increases of mixotrophic and autotrophic cultures compared to low-light intensity conditions (Figure 1c)
G. sulphuraria is modulated in response to high-light intensity exposure and mixotrophic conditions
Summary
Specialized microorganisms that populate harsh environments characterized by extreme temperature, pH, and salinity, are called extremophiles [1]. Most of them are prokaryotic, some eukaryotes belong to this group of microorganisms. Galdieria sulphuraria is a eukaryotic red alga belonging to the Cyanidiales family. It is adapted to scorching temperatures (up to 56 ◦ C) and acidic pH (0.5–3.0) [2]. This alga is the only species of the Cyanidiales that can grow autotrophically, mixotrophically, and heterotrophically. It possesses the ability to tolerate various stresses and accumulate beneficial compounds [3]. G. sulphuraria is considered a new model organism for biotechnology due to its tolerance mechanisms to environmental stresses [4]. Further investigations are required before full biotechnological potential can be reached
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