’Blood of the glaciers’: how an algae adapts to life in the snow

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Three-dimensional architecture of the Sanguina nivaloides snow alga cell. Grégor
Three-dimensional architecture of the Sanguina nivaloides snow alga cell. Grégory Si Larbi (LPCV)

In spring, Alpine glaciers sometimes turn a thin layer of red or orange. This phenomenon, known as "glacier blood", is due to the proliferation of a microscopic alga called Sanguina nivaloides. Scientists 1 from CNRS, CEA, Météo-France, INRAE and Grenoble Alpes University have been studying this organism, which forms the backbone of a little-known snow ecosystem. Their results 2 have just been published in Nature Communications. Firstly, they showed that the alga does not live in the ice crystals, but thrives in the liquid water that circulates in the snow, on the periphery of these crystals. The biologists then analyzed the algae’s cellular architecture using 3D electron microscopy. This revealed the adaptations that enable it to multiply in the snow. For example, they observed that Sanguina ’s cell membrane is criss-crossed by tiny wrinkles that increase its surface area of contact with the outside world. This enables the algae to better extract the ions necessary for growth from an extremely nutrient-poor environment.

The inside of the cell was also full of surprises. The alga has a single chloroplast. Inside the chloroplast, the thylakoids - the lamellar structures where photosynthesis takes place - are not oriented in a single direction, as in most plants. In Sanguina nivaloides , they fan out to receive light from all directions. This adaptation is specific to life in the snow, an environment where light is diffused and reflected as in a hall of mirrors. The mitochondria, the cell’s energy powerhouses, are positioned directly on the periphery of the chloroplast to use the starch it synthesizes. Finally, the research team turned its attention to the algae’s red pigments. These do not, as previously thought, serve to protect the cell nucleus from UV radiation. Consisting of carotenoids, they would enable the algae to protect itself against the deleterious effects of oxidizing free radicals, in an environment enveloped in very bright light.

After the snow melts, the algae finds itself in the soil and undergoes a veritable metamorphosis to adapt to a radically different environment. Scientists now want to understand this never-before-studied process. Time is of the essence, as the entire ecosystem dependent on Sanguina nivaloides is threatened by climate change and reduced snow cover in the mountains.

1 Working at the Laboratoire de physiologie cellulaire et végétale (CNRS/CEA/UGA/Inrae), the Centre national de recherches météorologiques (CNRS/Météo-France), the Laboratoire Modélisation et exploration des matériaux (CEA/UGA), the Institut de biologie structurale (CNRS/CEA/UGA), and the Unité d’appui et de recherche Jardin du Lautaret (CNRS/UGA).


2 This work was supported by the ANR as part of the AlpAlga program, and is the first to be published with the help of the Kilian Jornet Foundation.

Bibliography

Adaptative traits of cysts of the snow alga Sanguina nivaloides unveiled by 3D subcellular imaging. E. Maréchal, et al. Nature Communications , November 18, 2023.
DOI : https://doi.org/10.1038/s41467­’023 -43030-7




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