Different resistance mechanisms to desiccation of a pair of Nostoc sp. strains from aquatic and terrestrial habitats of Antarctica

Cyanobacteria are photosynthetic autotrophic micro-organisms that can survive in a variety of extreme environments around the world, such as polar regions. They usually live in association with other organisms and form biological soil crusts in terrestrial environments or thick benthic mats in aquatic environments, where they can develop particular structures such as benthic pinnacle mats. Cyanobacteria 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 mechanisms is necessary to clarify how these processes work. In the present study, the ecophysiological performance of two Nostoc sp. strains was investigated under dehydration and subsequent re-hydration stress. The chosen pair of strains shares 100 % of 16S rRNA gene similarity but have different ecologies. Strain ULC180 and ULC008 from the BCCM culture collection were isolated from a granitic outcrop in the Sør Rondane Mountains (East Antarctica) and from an Antarctic lake (Larsemann Hills, East Antarctica), respectively. To determine their capacity to withstand desiccation, both strains were cultured in BG110 medium, then left dehydrating onto filters placed into a desiccation chamber until complete desiccation (Fv/Fm around 0) and re-hydrated for up to 72 h. Samples for pigments, exopolysaccharide (EPS) and RNA extractions were taken when the desiccation was complete and after 10 min, 2 h, 24 h and 72 h of rewetting whilst Fv/Fm was measured before sampling. Our preliminary EPS and pigments results suggest a higher resistance of the terrestrial strain to desiccation. However further analyses of the gene expression by RNA-seq are in progress for a better understanding of the different mechanisms developed by these two strains