WHAT DOES IT TAKE (GENOME WISE) FOR MICROORGANISMS TO ADAPT TO HARSH ENVIRONMENTAL CONDITIONS

Microorganisms inhabiting biological desert soil crusts (BSC) are likely equipped to cope with one of the harshest environmental conditions on earth including daily hydration/dehydration cycles, high irradiance and extreme temperatures. Of particular interest are the unicellular photosynthetic species as these acquired genes allowing them not only to survive, but also maintain active and efficient photosynthesis in such extreme conditions. From both the basic science and biotechnological/agricultural perspectives identification and characterization of these genes may contribute to our understanding of stress biology and enhance tolerance of less tolerant organisms in view of global climate changes. Our two cases of study are Leptolyngbya ohadii, a filamentous cyanobacterium able to revive even after severe dehydration, and Chlorella ohadii, a green alga presenting the fastest growth rate for a photosynthetic eukaryote and unparalleled resistance to high light. Using full genome sequencing, transcriptome analyses of isolated cultures under optimal and stress conditions, comparative genomics and correlating them with physiological data we found groups of both known and novel genes, likely to play significant role in tolerance for desiccation and to extreme high light intensities. Comparative genomics identified a set of 36 genes present in desiccation-tolerant but not in dehydration-sensitive cyanobacteria. The C. ohadii genome analysis revealed a set of genes that are regulated by light and not found in any other public database. These analyses may contribute to the identification of novel stress tolerance pathways, making them potential targets for genetically improved crop plants.