Abstract
The geomicrobiological characterization of the water column and sediments of Río Tinto (Huelva, Southwestern Spain) have proven the importance of the iron and the sulfur cycles, not only in generating the extreme conditions of the habitat (low pH, high concentration of toxic heavy metals), but also in maintaining the high level of microbial diversity detected in the basin. It has been proven that the extreme acidic conditions of Río Tinto basin are not the product of 5000 years of mining activity in the area, but the consequence of an active underground bioreactor that obtains its energy from the massive sulfidic minerals existing in the Iberian Pyrite Belt. Two drilling projects, MARTE (Mars Astrobiology Research and Technology Experiment) (2003–2006) and IPBSL (Iberian Pyrite Belt Subsurface Life Detection) (2011–2015), were developed and carried out to provide evidence of subsurface microbial activity and the potential resources that support these activities. The reduced substrates and the oxidants that drive the system appear to come from the rock matrix. These resources need only groundwater to launch diverse microbial metabolisms. The similarities between the vast sulfate and iron oxide deposits on Mars and the main sulfide bioleaching products found in the Tinto basin have given Río Tinto the status of a geochemical and mineralogical Mars terrestrial analogue.
Highlights
The NASA Astrobiology roadmap [1] highlights the interest in extreme environments and the microorganisms that live in them in evaluating the possible existence of life beyond Earth
These results prove that multicellular complex systems can develop in some extreme conditions, like those existing in Río Tinto
In contrast to conventional acid rock drainage (ARD) models, oxidants to drive the system are supplied by the rock matrix. Mobilization of these sources by ground water is required to promote microbial metabolisms. These observations confirmed the hypothesis that microorganisms are active in the subsurface of the Iberian Pyrite Belt (IPB) and are responsible for the characteristic extreme conditions detected in the Tinto basin
Summary
The NASA Astrobiology roadmap [1] highlights the interest in extreme environments and the microorganisms that live in them in evaluating the possible existence of life beyond Earth. Acidophiles are of special interest, because the environments in which they thrive are the product of the chemolithotrophic metabolism of microorganisms that obtain energy from reduced mineral substrates and are not adaptations to geophysical constraints, as with most extremophiles. The discovery that some strict chemolithotrophs, such as Leptospirillum ferrooxidans, thrive using ferrous iron as their only source of energy and that their role in bioleaching operations and the generation of AMDs is much more important than previously thought has completely changed this point of view [10]. Río Tinto are known to have been in operation more than 5000 years ago [17]
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