Goldschmidt Conference Abstracts 2005 A227 Controls on Microbial Processes

Microbial interactions with sulfide The Vulcano hydrothermal system: and arsenite in an acidic geothermal Microbial community structure, spring in Yellowstone National Park novel isolates, and geochemical

SETH D’IMPERIO, CORINNE LEHR AND energy sources TIMOTHY R. MCDERMOTT J. P. AMEND, K. L. ROGERS, A. RUSCH AND C. GAMMON Dept. Land Resources and Environmental Sciences, and Department of Earth & Planetary Sciences, Washington Thermal Biology Institute Montana State University, University, St. Louis, MO 63130 USA Bozeman, MT 59717 (sethd@mymail. msu.montana.edu; ([email protected], [email protected]) [email protected]; timmcder@ montana.edu)

The hydrothermal system of Vulcano Island, Italy is We are studying the ecophysiology of microbial arguably the best-studied shallow marine vent environment in populations inhabiting an acid-sulfate-chloride geothermal the world. This system is the type locality for some of the spring in Norris Geyser Basin, Yellowstone National Park. most famous hyper-thermophiles, including Thermotoga Source water temperature ranges from 63 to 73 °C and pH maritima, Aquifex aeolicus, and Archaeoglobus fulgidus. In between 3.1 to 3.3. Electron donors present at concentrations addition, geochemical analyses and modeling have revealed capable of supporting chemolithoautotrophic-based primary hundreds of energy-yielding redox reactions that could support production include Fe(II), H , H S, and As(III). The spring is 2 2 autotrophic and heterotrophic communities. chemostat-like in that the bioavailability of these energy We have applied several techniques to characterize the sources is constant, although absolute concentrations can vary interface of hydrothermal geochemistry and microbial somewhat, and aqueous chemistry measurements have diversity at Vulcano. Using geochemically-designed media, revealed the presence of numerous chemical (and temperature) we isolated the first O -tolerant member of the archaeal order gradients occurring as a function of distance from the point of 2 ( helgesonii) and a novel spring discharge. In-field assays demonstrate significant thermophilic, autotrophic, sulfate-reducing bacterium that is microbial oxidation of As(III), but only in specific zones in the only 92% identical in its 16S rRNA gene sequence to any spring outflow channel where H S is depleted. We are 2 cultivated organism. The prokaryotic communities in three combining biogeochemical measurements, phylogenetic Vulcano sediment samples, determined by flourescent in situ analysis, and pure culture experiments to model in situ hybridization (FISH), were dominated by (60-80% of As(III)-H S-microbe interactions in order to explain the 2 probe-detected cells). However, the abundances of specific apparent zonation of the As(III) oxidation. An As(III)- archaeal groups range significantly across the sites: 11-16% oxidizing Hydrogenobaculum strain was isolated and used to for the Thermococcales, 6-15% for the Archaeoglobales and show that sulfide inhibits As(III) oxidation. Additional in-field 17-26% for the Crenarchaeota. In one case, the disappearance experiments re-examined As(III) oxidation in the spring mats of the aerobe, Aquifex, from the microbial community by manipulating H S concentrations and found that the 2 corresponded to a marked decline in O . Diverse archaeal microorganisms in the spring mats appear enzymatically 2 communities were also noted in 16S rRNA gene surveys. equipped to oxidize As(III), but are inhibited to do so if Archaeal diversity in a thermal well consisted of 17 unique appreciable dissolved H S is present (> 5-10 M H S). H S 2 2 2 phylotypes and was dominated by a group of uncultured, appears to not be toxic, but rather acts as a reversible, deeply-branching Crenarchaeota. In contrast, a thermal vent competitive inhibitor of the As(III) oxidase enzyme, an with similar temperature and pH contained 6 unique archaeal example of a geochemical control on a microbial process. phylotypes, all distinct from those found in the well. Documented compositional and energetic diversity appears to be directly linked to prokaryotic community structure and diversity.