Microbial survival and adaptation in extreme terrestrial environments – the case of the Dallol geothermal area in Ethiopia

In the quest to find life on other planets, specific extreme terrestrial environments are studied as analogues to present or past conditions on other bodies of our Solar System and beyond. These terrestrial extreme environments often harbour microbial life of high diversity and abundance. These microbes, mostly Bacteria and Archaea, develop survival and adaptation strategies enabling them to withstand harsh conditions. The physico-chemical boundaries for life on Earth are very broad and extreme environments on Earth are highly diversified. Extreme Earth ecosystems bear similarities to past or present environments on planets such as Mars and Venus but may also be analogues to certain moons of gas giants, such as Titan, Europa, and Enceladus. In this review we (1) report the recently described planetary field analogue environment from the Dallol geothermal area in the Danakil Depression, Ethiopia, in which polyextremophilic physical and chemical boundaries for life on Earth coexist; and (2) summarise the physicochemical conditions of extreme terrestrial environments in comparison to extra-terrestrial examples within the framework of our knowledge of microbial life and its adaptation to extremity, suggesting whether and how life could adapt to present or past potential extra-terrestrial habitats. We also explore the distribution and geographical dispersal of microorganisms that inhabit these terrestrial ecosystems and discuss implications for Panspermia.