Desiccation tolerance and growth-temperature requirements of Coccomyxa (Trebouxiophyceae, Chlorophyta) strains from Antarctic biological soil crusts

The genus Coccomyxa is frequently present in biological soil crusts from temperate regions but has also been found in Antarctic soils. Strain NIES 2166 (Coccomyxa subellipsoidea) from continental South Victoria Land is described as a model organism for cold adaptation (Blanc et al. 2012) although it has been cultivated for more than 50 years under artificial conditions. In order to test whether this isolate still kept physiological traits for Antarctic conditions or exhibited acclimation/adaptation to culturing, it was ecophysiologically compared with three recently isolated Coccomyxa strains from soil samples collected at the Antarctic Peninsula. Additionally, the investigated strains were tested for potential endemism. Molecular analysis based on ITS rDNA identified the three newly isolated strains also as C. subellipsoidea. The effective quantum yield of photosynthesis was examined during controlled short-term desiccation (at relative air humidity c. 10%) and after rehydration. Growth rates were determined over a temperature gradient from 4.6 to 34.8 °C. The results indicate cold tolerance and drought tolerance among all tested strains which are slightly more developed in the continental strain NIES 2166 although 50 years passed since isolation. Therefore it is assumed that strain NIES 2166 can still be recommended to test traits of cold adaptation but psychrophilic behavior, and therefore endemism, can be excluded among all str