Deep subsurface sulfate reduction and methanogenesis in the Iberian Pyrite Belt revealed through geochemistry and molecular biomarkers.

The Iberian Pyrite Belt (IPB, southwest of Spain), the largest known massive sulfide deposit, fuels a rich chemolithotrophic microbial community in the Río Tinto area. However, the geomicrobiology of its deep subsurface is still unexplored. Herein, we report on the geochemistry and prokaryotic diversity in the subsurface (down to a depth of 166 m) of the Iberian Pyritic belt using an array of geochemical and complementary molecular ecology techniques. Using an antibody microarray, we detected polymeric biomarkers (lipoteichoic acids and peptidoglycan) from Gram-positive bacteria throughout the borehole. DNA microarray hybridization confirmed the presence of members of methane oxidizers, sulfate-reducers, metal and sulfur oxidizers, and methanogenic Euryarchaeota. DNA sequences from denitrifying and hydrogenotrophic bacteria were also identified. FISH hybridization revealed live bacterial clusters associated with microniches on mineral surfaces. These results, together with measures of the geochemical parameters in the borehole, allowed us to create a preliminary scheme of the biogeochemical processes that could be operating in the deep subsurface of the Iberian Pyrite Belt, including microbial metabolisms such as sulfate reduction, methanogenesis and anaerobic methane oxidation.

First prokaryotic biodiversity assessment using molecular techniques of an acidic river in Neuquén, Argentina.

Two acidic hot springs close to the crater of Copahue Volcano (Neuquén, Argentina) are the source of the Río Agrio. The river runs several kilometres before flowing into Caviahue Lake. Along the river, temperature, iron, other metal and proton concentrations decrease gradually with distance downstream. From the source to the lake and depending on the season, pH can rise from 1.0 (or even less) to about 4.0, while temperature values decrease from 70°C to 15°C. Water samples were taken from different stations on the river selected according to their physicochemical parameters. In order to assess prokaryotic biodiversity throughout the water column, different and complementary molecular biology techniques were used, mainly in situ hybridisation and 16S rRNA gene cloning and sequencing. All microorganisms found are typical of acidic environments. Sulphur-oxidizing bacteria like Acidithiobacillus thiooxidans and Acidithiobacillus albertensis were detected in every station. Moderately thermophile iron- and sulphur-oxidizing bacteria like members of Alicyclobacillus and Sulfobacillus genera were also ubiquitous. Strict iron-oxidizing bacteria like Leptospirillum and Ferrimicrobium were present at the source of the river, but disappeared downstream where iron concentrations were much lower. Iron-oxidizing, mesophilic Ferroplasma spp. were the main archaea found. The data presented in this work represent the first molecular assessment of this rare natural acidic environment.