Geomicrobiology of Hydrothermal Vents in Yellowstone Lake: Phylogenetic and Functional Analysis suggest Importance of Geochemistry (Invited)

Yellowstone Lake (Yellowstone National Park, WY, USA) is a large, high-altitude, fresh-water lake that straddles the most recent Yellowstone caldera, and is situated on top of significant hydrothermal activity. An interdisciplinary study is underway to evaluate the geochemical and geomicrobiological characteristics of several hydrothermal vent environments sampled using a remotely operated vehicle, and to determine the degree to which these vents may influence the biology of this young freshwater ecosystem. Approximately six different vent systems (locations) were sampled during 2007 and 2008, and included water obtained directly from the hydrothermal vents as well as biomass and sediment associated with these high-temperature environments. Thorough geochemical analysis of these hydrothermal environments reveals variation in pH, sulfide, hydrogen and other potential electron donors that may drive primary productivity. The concentrations of dissolved hydrogen and sulfide were extremely high in numerous vents sampled, especially the deeper (30-50 m) vents located in the Inflated Plain, West Thumb, and Mary Bay. Significant dilution of hydrothermal fluids occurs due to mixing with surrounding lake water. Despite this, the temperatures observed in many of these hydrothermal vents range from 50-90 C, and elevated concentrations of constituents typically associated with geothermal activity in Yellowstone are observed in waters sampled directly from vent discharge. Microorganisms associated with elemental sulfur mats and filamentous ‘streamer’ communities of Inflated Plain and West Thumb (pH range 5-6) were dominated by members of the deeply-rooted bacterial Order Aquificales, but also contain thermophilic members of the domain Archaea. Assembly of metagenome sequence from the Inflated Plain vent biomass and to a lesser extent, West Thumb vent biomass reveal the importance of Sulfurihydrogenibium-like organisms, also important in numerous terrestrial geothermal outflow channels of YNP. Analysis of functional genes present in the consensus metagenome sequence representing these populations indicate metabolic potential for oxidation of reduced sulfur and hydrogen, both of which are present at high concentrations in these vent ecosystems. Metagenome sequence of biomass associated with sediments from hydrothermal vents at Mary Bay (50 m depth) suggest greater archaeal and bacterial diversity in this environment, which may be due to higher concentrations of hydrogen, iron, and manganese measured in these environments. Results from metagenome sequence and modest 16S rRNA gene surveys from hydrothermal vent biomass indicate that several groups of novel thermophilic archaea inhabit these sites, and in many cases, are represented by organisms not found in YNP terrestrial geothermal environments that have been characterized to date. The hydrothermal vents from Inflated Plain and West Thumb indicate a linkage between various geochemical attributes (sulfide, hydrogen) and the metabolic potential associated with dominant Aquificales populations present in these communities.