Unveiling the molecular mechanisms of the stress resilience of High Arctic Klebsormidium flaccidum: A multifaceted study.

The green alga Klebsormidium is found worldwide in terrestrial and freshwater habitats. A novel strain was isolated from biological soil crusts on Breinosa Mountain in Svalbard (High Arctic, 78°N) to investigate its adaptation to extreme Arctic conditions, characterized by low temperatures and short periods of snow-free ground. Genetic analyses confirmed the strain's identity as Klebsormidium flaccidum, showing high genetic similarity to strains from polar and temperate habitats. This study explored the effects of nitrogen starvation, cold stress, desiccation, and freezing, focusing on molecular responses and stress resilience. Nitrogen starvation strongly impacted metabolic activity, while cold and desiccation stress had more subtle effects, with K. flaccidum showing permanent stress-related gene expression instead of acute responses. Cold acclimation was found to enhance desiccation and freezing tolerance, while nitrogen starvation worsened the effects of these stresses. These results suggest that K. flaccidum CCALA 1182 is inherently capable of withstanding fluctuating environmental stresses, highlighting its potential for survival in diverse and harsh ecosystems.