Terrestrial subsurface geomicrobiology is a matter of growing interest on many levels. From a fundamental point of view, it seeks to determine whether life can be sustained in the absence of Sun radiation. From an astrobiological point of view, it is an interesting model for early life on Earth, as well as a representation of life as it could occur in other planetary bodies. Río Tinto is an unusual extreme acidic environment due to its size (100 km), constant acidic pH (mean pH 2.3), elevate concentration of heavy metals and high level of microbial diversity, mainly eukaryotic. Río Tinto rises in the core of the Iberian Pyritic Belt (IPB), one of the biggest sulfidic ore deposits in the world. Today it is clear that the extreme characteristics of Río Tinto are not due to acid mine drainage resulting from mining activity, but to the chemolithotrophic microorganisms thriving in the high concentration of metal sulfides of the IPB.
To explore the hypothesis that a continuous underground reactor of chemolithotrophic microorganisms thriving in the rich sulfidic minerals of the IPB is responsible for the extreme conditions found in the river, we propose a drilling project to detect the subsurface microbial activity, the potential resources to support these microbial communities, and to follow the in situ geomicrobiological evolution in real time.
In this project, we propose to explore the Río Tinto Mars analog at deep-basement regions (200-1000 m) by means of new approaches, comprising:
- detection of life and estimation of the microbial diversity at the drilling site providing an instant picture of the subsurface habitat; and
- real time monitoring, inside the borehole, of physicochemical parameters and biological activity (e.g. pH, Eh, ionic composition, dissolved gases, etc) generating essential information to recognize matter and energy fluxes.
All these processes are associated to long-term changes in the underground habitats and are not fully understood based on seasonal discontinuous subsurface analysis by water and gas sampling. To achieve these goals we will analyze cores and fluids in the field site using new and powerful tools: antibody-microarray based biosensors for in situ identification of microorganisms and their metabolic products, portable mineral and geochemical analyzers. After drilling, and for downhole monitoring subsurface biogeochemistry, sensors capable to perform and survive at the extreme conditions of the habitat will be developed and display to monitor in real time geomicrobiological parameters such as pH, Eh, conductivity, gases (H2, CH4, CO2, nitrogen oxides), cations and inions. These data would allow to analyze in real time the evolution of these biogeochemical parameters as well as the associated microbial activities. In addition, molecular ecology techniques as well as metagenomic and transcriptomics approaches will validate and expand the in situ investigations in the laboratory.