Xerotolerance: A New Property in Genus.

The highly xerotolerant bacterium classified as sp. Helios isolated from a solar panel in Spain showed a close relationship to 255-15 isolated from Siberian permafrost. Xerotolerance has not been previously described as a characteristic of the extremely diverse genus, but both strains Helios and 255-15 showed higher xerotolerance than that described in the reference xerotolerant model strain  . Significant changes observed in the cell morphology after their desiccation suggests that the structure of cellular surface plays an important role in xerotolerance. Apart from its remarkable resistance to desiccation, sp. Helios strain shows several polyextremophilic characteristics that make it a promising chassis for biotechnological applications. sp. Helios cells produce nanoparticles of selenium in the presence of selenite linked to its resistance mechanism. Using the plasmid pRCR12 that harbors a cherry marker, we have developed a transformation protocol for sp. Helios strain, being the first time that a bacterium of genus has been genetically modified. The comparison of sp. Helios and 255-15 genomes revealed several interesting similarities and differences. Both strains contain a complete set of competence-related DNA transformation genes, suggesting that they might have natural competence, and an incomplete set of genes involved in sporulation; moreover, these strains not produce spores, suggesting that these genes might be involved in xerotolerance.