| Summary: | Cyanobacteria can survive in extreme environments, such as drylands or polar regions, and are found in aquatic or terrestrial habitats around the world. For example, they live in associations with other organisms to form biological soil crusts. They have developed different resistance traits to cope with extreme and contrasted environments, such as the production of pigments to absorb UV radiation or a polysaccharidic matrix to withstand desiccation. However, a better understanding of their ecophysiological responses is necessary to clarify how these processes work. In the present study, we analyzed the ecophysiological performance of two Nostoc commune strains under two stress factors: salinity and UV radiation. This pair of strains has > 99% 16S rRNA gene similarity. Strain ULC002 and UAM817 were isolated from a microbial mat in an Antarctic lake (Larsemann Hills, East Antarctica) and from a biological soil crust in a semiarid region (limestone quarry in Gádor, SE Spain), respectively. To determine their capacity to withstand salinity, both strains were cultured in BG110 medium with increasing NaCl concentrations (from 0 M to 2.5 M) for 43 days. To analyze their resistance to UV radiation, both strains were incubated for 3 days under a UV-B and –A radiation of 2 W/m2 and 10 W/m2, respectively.The chlorophyll a, scytonemin and carotenoid contents were extracted from the cultures and measured with a spectrophotometer at different time points, as well as the photosynthetic efficiency (Fv/Fm, measured by Pulse-Amplified Modulation spectrophotometry). Our results show a higher resistance of the Antarctic strain to salinity, as it could grow in concentrations of up to 0.2 M NaCl, compared to the biocrust-forming strain that showed a negative growth rate at salinity concentrations above 0.05 M. Both strains showed a comparable increase in photosynthetic stress with salinity. Similarly, they also showed a decrease in Fv/Fm values under the UV radiation stressor, with only the biocrust-forming strain showing a ...
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