Figure S1. Synchrotron X-ray diffraction patterns of samples collected from Joseph's Coat, Monarch Geyser, and Cistern Spring (Yellowstone National Park). JC3A bottom is composed primarily of quartz (PDF#46-1045), while JC3A sediment is composed primarily of quartz (PDF#46-1045), pyrite (PDF#42-1340), and stibnite (PDF#42-1393). Monarch Geyser and Cistern Spring both contain distinct patterns representative of elemental sulfur (PDF#08-0247 and PDF#89-2600, respectively).

Figure S2. Linear combination antimony EXAFS fitting of solid phases present in samples collected from Joseph's Coat Hot Spring (Yellowstone National Park). All samples exhibit a large contribution from stibnite (Sb2S3), with most remaining variation explained by contributions from Sb(V) [JC3A south and northwest samples represent the stibnitic metallic phase vs. the cooler JC3A sediment]. Least-squares fitting confirmed that Sb(III) standards other than stibnite (e.g., Na antimonite, Sb2O3) represented less than 10% mole fraction of antimony in all samples (1 reduced chi-square parameter to indicate goodness of fit).

gbi12015-sup-0002-TableS1-S4.docxWord document32K

Table S1. Average source water chemistry (total dissolved concentration) of three sulfidic geothermal springs located at Joseph's Coat Springs (JC3) and Norris Geyser Basin (NGB), Yellowstone National Park (standard deviations in parentheses).

Table S2. Exergonic (i.e., thermodynamically-favorable) oxidation-reduction reactions involving aqueous and solid phase species important in geothermal environments of Joseph's Coat Spring, Monarch Geyser and Cistern Spring. Reactions highlighted in gray involve sulfur species. The free energy values (&Grxn, kJ mol−1 e−1) for each reaction are given at 85 oC (&Grxn calculated using activities of chemical species predicted using aqueous chemical modeling, MINTEQ).

Table S3. Saturation indices [log (IAP/KSP)] with respect to various mineral phases calculated after chemical speciation with the aqueous equilibrium program, Visual MINTEQ (IAP = ion activity product; Ksp = solubility product constant; SI> 0 = over-saturation; SI<0 = under-saturation).

Table S4. Evaluation of potential carbon and energy sources and possible electron acceptors supporting growth of Pyrobaculum-like strain WP30. Experiments were conducted in 100% synthetic medium contained in 10 mL serum bottles at 75 oC and pH 6.1 [entries highlighted in gray supported significant growth and/or production of sulfide; nd = not detectable; YE = yeast extract].

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