Insights into the biology and phylogeny of Chloromonas polyptera (Chlorophyta), an alga causing orange snow in Maritime Antarctica

In Antarctica, mass accumulations of psychrophilic algae cause striking phenomena like green, orange, or red snow. This occurs during summer, when coastal snowfields start to melt, become waterlogged and photoautotrophs can thrive. Chloromonas polyptera (Fritsch) Hoham, Mullet & Roemer is a unicellular species that causes orange snow in the vicinity of penguin rockeries. It has been recognized for many decades because of the distinct habitat and the characteristic morphology of cysts with elongated flanges on the outer cell wall. However, closer investigations concerning the ecology or physiology have been sparse so far. Field material was collected from two sites on the Antarctic Peninsula to find out more about metabolic and cellular strategies. The results were compared with a closely related species from high alpine locations, Chloromonas nivalis (Chodat) Hoham & Mullet. Despite the geographical distance, C. polyptera shares several physiological strategies with the alpine relative, such as the formation of cyst stages, saccharose and glycerol as main soluble carbohydrates and the abundant accumulation of the carotenoid astaxanthin. Moreover, photosynthesis is adapted to temperatures of about 1 degrees C. The molecular phylogeny confirmed a close relationship of C. polyptera to other Chloromonas species isolated from snow. Chloromonas polyptera seems to be exclusive to coastal Antarctic ecosystems influenced by animal nutrient input.