Dataset Information

A Polyextreme Hydrothermal System Controlled by Iron: The Case of Dallol at the Afar Triangle.

ABSTRACT: One of the latest volcanic features of the Erta Ale range at the Afar Triangle (NE Ethiopia) has created a polyextreme hydrothermal system located at the Danakil depression on top of a protovolcano known as the dome of Dallol. The interaction of the underlying basaltic magma with the evaporitic salts of the Danakil depression has generated a unique, high-temperature (108 °C), hypersaline (NaCl supersaturated), hyperacidic (pH values from 0.1 to -1.7), oxygen-free hydrothermal site containing up to 150 g/L of iron. We find that the colorful brine pools and mineral patterns of Dallol derive from the slow oxygen diffusion and progressive oxidation of the dissolved ferrous iron, the iron-chlorine/-sulfate complexation, and the evaporation. These inorganic processes induce the precipitation of nanoscale jarosite-group minerals and iron(III)-oxyhydroxides over a vast deposition of halite displaying complex architectures. Our results suggest that life, if present under such conditions, does not play a dominant role in the geochemical cycling and mineral precipitation at Dallol as opposed to other hydrothermal sites. Dallol, a hydrothermal system controlled by iron, is a present-day laboratory for studying the precipitation and progressive oxidation of iron minerals, relevant for geochemical processes occurring at early Earth and Martian environments.

SUBMITTER: Kotopoulou E

PROVIDER: S-EPMC6380227 | biostudies-literature | 2019 Jan

REPOSITORIES: biostudies-literature

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A Polyextreme Hydrothermal System Controlled by Iron: The Case of Dallol at the Afar Triangle.

Kotopoulou Electra E Delgado Huertas Antonio A Garcia-Ruiz Juan Manuel JM Dominguez-Vera Jose M JM Lopez-Garcia Jose Maria JM Guerra-Tschuschke Isabel I Rull Fernando F

ACS earth & space chemistry 20181206 1

One of the latest volcanic features of the Erta Ale range at the Afar Triangle (NE Ethiopia) has created a polyextreme hydrothermal system located at the Danakil depression on top of a protovolcano known as the dome of Dallol. The interaction of the underlying basaltic magma with the evaporitic salts of the Danakil depression has generated a unique, high-temperature (108 °C), hypersaline (NaCl supersaturated), hyperacidic (pH values from 0.1 to -1.7), oxygen-free hydrothermal site containing up ...[more]

PMID: 30801049

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Project description:The remote Dallol Hot Springs, an active hydrothermal system in the volcanic region of Danakil (Ethiopia), is an interesting yet poorly studied polyextreme environment for investigating the limits of life. Here, we explored the presence of signs of life in five samples of sinter deposits at Dallol, by means of lipid biomarkers and stable isotope composition. The results reveal the existence of biological material with predominance of (presently or recently active) microbial sources, according to the relative abundance of low-over-high molecular weight moieties (n-alkanes, n-carboxylic acids, or n-alkanols), and the detection of diverse microbial-diagnostic compounds (i.e., monomethyl alkanes; C16:1 ?7, C18:1 ?9, C18:1 ?10, C18:2 ?6,9 and iso/anteiso C15 and C17 carboxylic acids; or short-chained dicarboxylic acids). The molecular lipid patterns at Dallol suggest a microbial community largely composed of thermophilic members of the Aquificae, Thermotogae, Chroroflexi, or Proteobacteria phyla, as well as microbial consortia of phototrophs (e.g., Cyanobacteria-Chloroflexi) in lower-temperature and higher-pH niches. Autotrophic sources most likely using the Calvin cycle, together with the acetyl coenzyme A (CoA) pathway, were inferred from the depleted bulk ?13C ratios (-25.9/-22.6‰), while sulfate-reducing bacteria were considered according to enriched sulfate (7.3/11.7‰) and total sulfur (20.5/8.2‰) ?34S ratios. The abundance of functionalized hydrocarbons (i.e., n-carboxylic acids and n-alkanols) and the distinct even-over-odd predominance/preference on the typically odd n-alkanes (CPIalkanes ? 1) pointed to active or recent microbial metabolisms. This study documents the detection of biosignatures in the polyextreme environment of Dallol and raises the possibility of finding life or its remnants in other remote locations on Earth, where the harsh environmental conditions would lead to expect otherwise. These findings are relevant for understanding the limits of life and have implications for searching for hypothetical life vestiges in extreme environments beyond Earth.

Project description:Determining the precise limits of life in polyextreme environments is challenging. Studies along gradients of polyextreme conditions in the Dallol proto-volcano area (Danakil salt desert, Ethiopia) showed the occurrence of archaea-dominated communities (up to 99%) in several hypersaline systems but strongly suggested that life did not thrive in the hyperacidic (pH ∼0), hypersaline (∼35% [wt/vol],) and sometimes hot (up to 108°C) ponds of the Dallol dome. However, it was recently claimed that archaea flourish in these brines based on the detection of one Nanohaloarchaeotas 16S rRNA gene and fluorescent in situ hybridization (FISH) experiments with archaea-specific probes. Here, we characterized the diversity of microorganisms in aerosols over Dallol, and we show that, in addition to typical bacteria from soil/dust, they transport halophilic archaea likely originating from neighboring hypersaline ecosystems. We also show that cells and DNA from cultures and natural local halophilic communities are rapidly destroyed upon contact with Dallol brine. Furthermore, we confirm the widespread occurrence of mineral particles, including silica-based biomorphs, in Dallol brines. FISH experiments using appropriate controls show that DNA fluorescent probes and dyes unspecifically bind to mineral precipitates in Dallol brines; cellular morphologies were unambiguously observed only in nearby hypersaline ecosystems. Our results show that airborne cell dispersal and unspecific binding of fluorescent probes are confounding factors likely affecting previous inferences of archaea thriving in Dallol. They highlight the need for controls and the consideration of alternative abiotic explanations before safely drawing conclusions about the presence of life in polyextreme terrestrial or extraterrestrial systems. IMPORTANCE Determining the precise limits of life in polyextreme environments is challenging. Confounding factors such as exogenous contamination and the abiotic formation of structures resembling cells need to be considered before concluding on the unambiguous development of microbial life in low-biomass environments. Here, we explored how these factors can affect contrasting reports about microbial life thriving in the hypersaline and hyperacidic brines of the Dallol geothermal field (Danakil Depression, Ethiopia). We show not only that aerosols actively transport a wide diversity of prokaryotic and eukaryotic cells over Dallol but also that, upon contact with the chaotropic hyperacidic brine, cells and DNA are rapidly degraded. We also show the extant occurrence of mineral (mostly silica-based) biomorphs that unspecifically bind fluorescent probes and dyes. Our study highlights the need for controls and the consideration of alternative abiotic explanations before safely drawing conclusions on the presence of life in polyextreme terrestrial or extraterrestrial systems.

Dataset Information

A Polyextreme Hydrothermal System Controlled by Iron: The Case of Dallol at the Afar Triangle.

Publications

A Polyextreme Hydrothermal System Controlled by Iron: The Case of Dallol at the Afar Triangle.

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