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

Sands in hot and cold deserts support more than one third of the global population and are often covered by a defined microbial community, the biological soil crust (BSC) that extends over approximately 40% of the Earth’s terrestrial surface. The BSCs play an essential role in the stabilization of sandy deserts and strongly influence their biotic composition. The organisms within the BSCs are exposed to one of the most extreme and fluctuating environmental regimes in nature. They face frequent hydration, mainly in the form of early morning dew and fog deposition, followed by desiccation as surface temperatures rise in the morning. In order to study the abilities of filamentous cyanobacteria to cope with this environment, we isolated a novel, axenic strain of Leptolyngbya sp from BSC samples withdrawn from the Nizzana field station in the Negev desert. To gain comprehensive physiological knowledge on the impact of the abiotic conditions, we constructed a fully automated environmental chamber capable of accurately simulating the dynamic abiotic conditions in the field. The main goal of our research is to reveal the molecular mechanisms that allow Leptolyngbya ohadii to cope with the conditions described. Results of experiments conducted in our research group assessing physiological recovery after desiccation by measuring oxygen evolution rate and fluorescence yield as a measure of cell viability and photosynthetic activity, clearly demonstrate the organism needs to activate a defense mechanism during desiccation in order to survive. In addition, whole-genome comparison to other organisms (Leptolyngbya ohadii genome has been sequenced and annotated) and identification of gene expression patterns of significant new genes using transcriptome and RT-qPCR analyses under various simulated ambient conditions is currently underway.