Specific jarosite biomineralization by Purpureocillium lilacinum, an acidophilic fungi isolated from Río Tinto.

Río Tinto (Huelva, southwestern Spain) is an extreme environment with a remarkably constant acidic pH and a high concentration of heavy metals, conditions generated by the metabolic activity of chemolithotrophic microorganisms thriving in the rich complex sulfides of the Iberian Pyrite Belt (IPB). Fungal strains isolated from the Tinto basin were characterized morphologically and phylogenetically. The strain identified as Purpureocillium lilacinum specifically induced the formation of a yellow-ocher precipitate, identified as hydronium-jarosite, an iron sulfate mineral which appears in abundance on the banks of Río Tinto. The biomineral was characterized by X-ray diffraction (XRD) and its formation was observed with high-resolution transmission electron microscopy (TEM) and scanning electron microscopy (SEM) coupled to energy-dispersive X-ray spectroscopy (EDX) microanalysis. Jarosite began to nucleate on the fungal cell wall, associated to the EPS, due to a local increase in the Fe(3+) /Fe(2+) ratio which generated supersaturation. Its formation has been also observed in non-viable cells, although with much less efficiency. The occurrence of P. lilacinum in an ecosystem with high concentrations of ferric iron and sulfates such as Río Tinto suggests that it could participate in the process of jarosite precipitation, helping to shape and control the geochemical properties of this environment.

From Río Tinto to Mars: the terrestrial and extraterrestrial ecology of acidophiles.

The recent geomicrobiological characterization of Río Tinto, Iberian Pyrite Belt (IPB), has proven the importance of the iron cycle, 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, both prokaryotic and eukaryotic, detected in the water column and the sediments. The extreme conditions of the Tinto basin are not the product of industrial contamination but the consequence of the presence of an underground bioreactor that obtains its energy from the massive sulfide minerals of the IPB. To test this hypothesis, a drilling project was carried out to intersect ground waters that interact with the mineral ore in order to provide evidence of subsurface microbial activities and the potential resources to support these activities. The oxidants that drive the system appear to come from the rock matrix, contradicting conventional acid mine drainage models. These resources need only groundwater to launch microbial metabolism. There are several similarities between the vast deposits of sulfates and iron oxides on Mars and the main sulfide-containing iron bioleaching products found in the Tinto. Firstly, the short-lived methane detected both in Mars' atmosphere and in the sediments and subsurface of the IPB and secondly, the abundance of iron, common to both. The physicochemical properties of iron make it a source of energy, a shield against radiation and oxidative stress as well as a natural pH controller. These similarities have led to Río Tinto's status as a Mars terrestrial analogue.