Ultra-small microorganisms in the polyextreme conditions of the Dallol volcano, Northern Afar, Ethiopia

Felipe Gómez,Jose M. Martínez,Hagos Miruts,Barbara Cavalazzi,Cristina Escudero,Karen Olsson-Francis,Nuria Rodríguez,Gian Gabriele Ori,Ricardo Amils

doi:10.1038/s41598-019-44440-8

Abstract

The Dallol geothermal area in the northern part of the Danakil Depression (up to 124–155 meter below sea level) is deemed one of the most extreme environments on Earth. The area is notable for being part of the Afar Depression, an incipient seafloor-spreading center located at the triple junction, between Nubian, Somali and Arabian plates, and for hosting environments at the very edge of natural physical-chemical extremities. The northern part of the Danakil Depression is dominated by the Assale salt plain (an accumulation of marine evaporite deposits) and hosts the Dallol volcano. Here, the interaction between the evaporitic deposit and the volcanisms have created the unique Dallol hot springs, which are highly acidic (pH ~ 0) and saline (saturation) with maximum temperatures ranging between 90 and 109 °C. Here we report for the first time evidence of life existing with these hot springs using a combination of morphological and molecular analyses. Ultra-small structures are shown to be entombed within mineral deposits, which are identified as members of the Order Nanohaloarchaea. The results from this study suggest the microorganisms can survive, and potential live, within this extreme environment, which has implications for understanding the limits of habitability on Earth and on (early) Mars.

Highlights

The study of environmental limits of life provides useful information for assessing the limits of habitability both on Earth and elsewhere in the Solar System[1,2]
In this system many protuberances can be observed (Figs 1b and 6A–C), which are generated by the precipitation of minerals from the superheated underground solutions
We demonstrated the presence of living ultra-small microorganisms in a multi-extreme environment with adverse conditions for life: extreme low pH (0.25), temperature (90 °C), redox potential, salinity and heavy metals content

Summary

Introduction

The study of environmental limits of life provides useful information for assessing the limits of habitability both on Earth and elsewhere in the Solar System[1,2] Understanding, and defining these limits, using extreme terrestrial environments and Earth analogues sites[3,4] is a crucial step in selecting sites for future life detection missions. The Dallol geothermal area (14°14′21′′N; 40°17′55′′E) is located in the northern part of the Danakil Depression[5]. This is a narrow lowland salt plain (up to 124 m below sea level) running inland, quasi-parallel to the coast of the Red Sea (Fig. 1a), which formed when part of the Red Sea was isolated during the Pleistocene. Sample pH T Cond Eh H2% CO2% Na Mg Al P K Ca Mn Fe Cu Zn Rb Sr Pb combination of these extreme chemical and physical parameters (e.g. temperature, pH, salinity and heavy metals) has resulted in a unique multi-extreme environment

Methods

Results

Conclusion