Biological soil crusts (BSC) are formed by the adhesion of sand particles to cyanobacterial exo- polysaccharides and play an important role in stabilizing sandy desert. Its destruction promotes desertification. The mechanisms that enable these organisms to cope with extreme temperatures, excess light and frequent hydration/dehydration cycles are largely unknown.
The genome of Leptolyngbya ohadii recently isolated from Nizzana BSC was sequenced and used to conduct comparative genomics of three desiccation tolerant cyanobacteria. This uncovered 46 unique genes, present only in desiccation tolerant cyanobacteria, some of them similar to genes involve in sporulation of the gram positive bacteria Bacillus sp.
In order to understand the molecular mechanisms taking place during desiccation we built an environmental chamber capable of accurately and reproducibly simulate the dynamic changes of environmental conditions in the crust. This chamber allows us to perform repetitive and accurate desiccation/rehydration experiments and follow the cyanobacterial physiological and molecular responses.
When we compared fast desiccation (less than 5 min) of isolated cyanobacteria to simulation of natural desiccation, we observed a 60% lower fluorescence recovery rate. The extent of damage from desiccation depended on the stress conditions during the dry period. These results suggest that cyanobacteria activate a protection mechanisms in response to desiccation stress. Gene expression patterns during desiccation are being analyzed in order to provide a better understanding of desiccation stress protection mechanisms.
