WHAT DISTINGUISHES THOSE THAT CAN FROM THOSE THAT CAN’T: THE DESICCATION TOLERANCE OF BIOLOGICAL SAND CRUST-INHABITING CYANOBACTERIA

Sands in hot and cold deserts are often covered by biological soil crusts (BSC). The BSCs stabilizes the sand, its destruction by anthropogenic and global change is a major cause of desertification. The BSCs are formed by the adhesion of the soil particles to extracellular polysaccharides excreted mainly by filamentous cyanobacteria, the pioneers and main primary producers in the BSC. The organisms inhabiting the BSCs are exposed to one of the most extreme and fluctuating environmental regimes in nature including frequent hydration/desiccation cycles, extreme irradiance, temperature amplitudes and vast osmotic potential changes. To study the abilities of filamentous cyanobacteria to cope with this environment, we isolated an axenic culture of Leptolyngbya sp named Leptolyngbya ohadii from BSC samples withdrawn from the Nizzana field station.

To overcome the natural variability in ambient conditions, we constructed a fully automated environmental chamber capable of accurately simulating the dynamic abiotic conditions in the field. Our physiological experiments showed that the ability to revive after desiccation is strongly affected by the dehydration rate, light and temperature conditions and also those during the desiccated phase. It clearly demonstrated that the organism must activate a defense mechanism which is modulated by various environmental cues during desiccation. Genomic information identified sets of genes present in cyanobacteria able to resurrect after desiccation but not in sensitive strains. trascriptome data, based on RNA Seq and RT-qPCR analyses, during desiccation under various simulated ambient conditions, is uncovering the genes involved and helps us to develop our current view, to be presented, on what distinguishes those that can (recover after desiccation) from those that can’t and the mechanisms involved.