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The hydrothermal fluid chemistry at El Tatio Geyser Field (ETGF) in northern Chile suggests that biogenic CO2–CH4 cycling may play an important role in water chemistry, and relatively low sulfate (0.6–1 mM) and high molecular hydrogen (H2) concentrations (67–363 nM) suggest that methanogenic Archaea are present in ETGF microbial mats. In this study, δ13C analysis of dissolved inorganic carbon and methane was not indicative of biogenic methane production (δ13CCH4 values ranging from −15‰ to −5.3‰); however, methanogenic Archaea were successfully cultured from each of the hydrothermal sites sampled. Sanger sequencing using universal Archaea primers identified putative methanogenic orders with varying metabolic capabilities, including Methanobacteriales, Methanomicrobiales and Methanosarcinales.

Subsurface karst aquifers receiving sulfidic water can host complex chemolithotrophic microbial communities that are capable of dissolving limestone, forming new karstic habitat. Neutrophilic sulfur-oxidizing bacteria use reduced sulfur compounds as energy rich substrate, potentially producing sulfuric acid as a geochemically reactive byproduct. The physicochemical relationship between a biofilm forming on a limestone surface and the extent of microbial influence on dissolution rate, however, are unknown. We investigated the rate of Madison limestone dissolution by sulfur-oxidizers both in the field at Lower Kane Cave, WY (LKC), and in the laboratory using continuous flow culture reactors and microbial mat collected from LKC. In the field, a microbial consortium rapidly colonized limestone chips forming a thick biofilm, with deep etching of mineral surfaces underneath. In the laboratory we found that a microbial biofilm oxidizing thiosulfate on the limestone surface accelerated dissolution rate up to 7 ti...

Microorganisms inhabiting terrestrial endolithic habitats are widespread in polar environments including the Antarctic Dry Valleys and the Canadian high Arctic. Their ability to survive in these harsh environments is a result of their finding protection from extremes in temperature, aridity, radiation and winds by colonizing nutrient-rich subsurface habitats that provide more amenable conditions for growth, often developing as vertically stratified communities that include fungi, algae, cyanobacteria and heterotrophic bacteria. Despite finding some refuge from climatic extremes, endolithic microorganisms commonly produce extracellular polysaccharides to avoid desiccation and minimize the damaging effects of freeze-thaw cycles. These microorganisms are geochemically reactive with their endolithic surroundings, observed as heterogeneous concentrations and distributions of metals resulting from mineral dissolution and precipitation reactions as well as element and nutrient release and cycling. Novel microsco...

Cryptoendolithic habitats in the Canadian high Arctic are host to a diverse assemblage of microorganisms including cyanobacteria, algae, fungi and heterotrophic bacteria. Communities grow as biofilms attached to mineral surfaces as well as within the open void spaces between grains and in many cases produce extracellular polysaccharides in response to the extreme environmental conditions. In situ observations of the cryptoendolithic habitat as well as ultrastructural examination of microorganisms show that this EPS provides a substrate for accumulation of allochthonous clay particles that enter the system by winds and rain. The lack of evidence for biomineralization within this habitat contrasts with similar environments in the Antarctic Dry Valleys, a consequence of warmer temperatures and wetter conditions that increase erosion rates and subsequent habitat destruction, effectively limiting the time possible for biomineralization by living microorganisms as well as the formation of biosignatures or micro...