The camels of the prokaryotic world

Hyper-arid deserts can be considered extreme environments with respect to their conditions of low humidity and low water activity. Traditionally we associate camels and cacti with the ability to survive in arid environments for extended periods without replenishing their water supply. Little is known about the diversity and ecology of prokaryotes in arid or hyper-arid regions. Using culturing and non-culturing molecular approaches, the presence of prokaryotes in the soils of such arid environments has been demonstrated. The numbers of culturable microorganisms in environments of varying water activity has been determined and representatives identified. The majority of organisms cultured are spore-forming Gram positive bacteria. In some cases similar organisms have been detected at the molecular level allowing the taxonomic status of such environtaxa to be predicted. A proportion of the organisms isolated were ionizing radiation resistant enforcing the link between desiccation resistance and ionizing radiation resistance.