Life at the Dallol geothermal area, Ethiopia- a Planetary Field Analog on Earth

Introduction

Dallol volcano area, proposed as a Mars analog, is considered one of the most extreme environment on Earth. It is located in the Danakil depression, a tectonically and volcanically active region in Ethiopia. The hydrothermal springs that compose the system discharge hyperacidic hot Fe-rich brines, which results in halite deposition when they contact with the atmosphere. As a result, Dallol geothermal area shows extremely high temperature (90-108°C in the springs), pH from -1.7 to 4, and supersaturated salt deposits [1-3].

Still, life finds a way. Despite these extreme features, microorganisms inhabiting Dallol geothermal region, as members of the class Nanohaloarchaea, have been described [3,4]. The analysis of the biodiversity that are surviving and thriving in such polyextreme system, as well as the study of their metabolic potential, could be fundamental to establish the habitability conditions to search for life on other planets.

Methods

We applied Shotgun metagenomics and Fluorescence in situ Hybridizations (FISH) methods to analyze the biodiversity and metabolic potential of Dallol geothermal area microbiome.

Results

Our results show the presence of both bacteria and archaea in the Dallol geothermal area, being Bacteria the most abundant domain in this environment. The detected microorganisms are mostly halophiles. However, there is a lower percentage of microorganisms described in extremely hot or acidic environments. FISH experiments corroborated that both bacteria and archaea are alive and active in the system.

Metagenomics analysis shows a predominance of metabolisms based on photosynthesis, heterotrophy and fermentation. In addition, metabolisms that use hydrogen and reduced sulfur compounds as an energy source stand out.

Additionally, genes related to the response to oxidative stress, heat shock, osmotic stress and detoxification have been detected, which could be involved in the adaptation of these microorganisms to the extreme conditions of the Dallol volcano area.

References

[1] Cavalazzi, B., et al. (2019). The Dallol geothermal area, Northern Afar (Ethiopia)—An exceptional planetary field analog on Earth. Astrobiology, 19(4), 553-578.

[2] Kotopoulou, E., et al. (2018). A polyextreme hydrothermal system controlled by iron: the case of Dallol at the Afar Triangle. ACS Earth and Space Chemistry, 3(1), 90-99.

[3] Carrizo, D., et al. (2019). Lipid Biomarker and Carbon Stable Isotope Survey on the Dallol Hydrothermal System in Ethiopia. Astrobiology, 19(12), 1474-1489.

[4] Gómez, F., et al. (2019). Ultra-small microorganisms in the polyextreme conditions of the Dallol volcano, Northern Afar, Ethiopia. Scientific reports, 9(1), 1-9.