Methanogenesis in the extreme acidic conditions of the Tinto river

An important subject of astrobiological interest is the study of microbial activities that can operate in the extreme conditions found in different planetary bodies. Of those, methanogenic activity is considered an interesting metabolism due to the nature of the substrates (hydrogen, formic acid, methanol, etc.) and the properties of methane, the metabolic product. Due to the peculiarities of the enzymes involved in methane production and the ecology of the microorganisms responsible of the process it is considered a relic of a primitive carbon cycle capable to operate in the subsurface in the absence of radiation (Stevens and McKinle, 1995, Pedersen, 2000), Gomez and Amils, 2002, Amils et al, 2004). Here we report the discovery of methanogenic activity associated to the anoxic sediments of The Tinto River Basin (Iberian Pyritic Belt), an extreme acidic environment product of the chemolithotrophic activity of iron- and sulfur-oxidizing microorganism. This finding is of astrobiological interest, specially in the context of life exploration on Mars (Stocker et al., 2003).