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Hundreds of active and dormant geothermal vents have been located on the floor of Yellowstone Lake, although characterization of the associated biology (macro or micro) has been extremely limited. Herein, we describe an aquatic moss ( Fontinalis) colony closely associated with vent emissions that considerably exceeded known temperature maxima for this plant. Vent waters were supersaturated with CO2, likely accommodating a CO2 compensation point that would be expected to be quite elevated under these conditions. The moss was colonized by metazoa, including the crustaceans Hyalella and Gammarus, a segmented worm in the Lumbriculidae family, and a flatworm specimen tentatively identified as Polycelis. The presence of these invertebrates suggest a highly localized food chain that derives from the presence of geothermal inputs and thus is analogous to the deep marine vents that support significant biodiversity. [ABSTRACT FROM AUTHOR]

The identification and characterization of genes involved in the microbial oxidation of arsenite will contribute to our understanding of factors controlling As cycling in natural systems. Towards this goal, we recently characterized the widespread occurrence of aerobic arsenite oxidase genes ( aroA-like) from pure-culture bacterial isolates, soils, sediments and geothermal mats, but were unable to detect these genes in all geothermal systems where we have observed microbial arsenite oxidation. Consequently, the objectives of the current study were to measure arsenite-oxidation rates in geochemically diverse thermal habitats in Yellowstone National Park (YNP) ranging in pH from 2.6 to 8, and to identify corresponding 16S rRNA and aroA genotypes associated with these arsenite-oxidizing environments. Geochemical analyses, including measurement of arsenite-oxidation rates within geothermal outflow channels, were combined with 16S rRNA gene and aroA functional gene analysis using newly designed primers to capture previously undescribed aroA-like arsenite oxidase gene diversity. The majority of bacterial 16S rRNA gene sequences found in acidic (pH 2.6–3.6) Fe-oxyhydroxide microbial mats were closely related to Hydrogenobaculum spp. (members of the bacterial order Aquificales), while the predominant sequences from near-neutral (pH 6.2–8) springs were affiliated with other Aquificales including Sulfurihydrogenibium spp., Thermocrinis spp. and Hydrogenobacter spp., as well as members of the Deinococci, Thermodesulfobacteria and β- Proteobacteria. Modified primers designed around previously characterized and newly identified aroA-like genes successfully amplified new lineages of aroA-like genes associated with members of the Aquificales across all geothermal systems examined. The expression of Aquificales aroA-like genes was also confirmed in situ, and the resultant cDNA sequences were consistent with aroA genotypes identified in the same environments. The aroA sequences identified in the current study expand the phylogenetic distribution of known Mo-pterin arsenite oxidase genes, and suggest the importance of three prominent genera of the order Aquificales in arsenite oxidation across geochemically distinct geothermal habitats ranging in pH from 2.6 to 8. [ABSTRACT FROM AUTHOR]

The hot springs in Yellowstone National Park, USA, provide concentrated microbial biomass and associated mineral crusts from which surface functional group (FG) concentrations and pKa distributions can be determined. To evaluate the importance of substratum surface reactivity for solute adsorption in a natural setting, samples of iron-rich sediment were collected from three different springs; two of the springs were acid-sulfate-chloride (ASC) in composition, while the third was neutral-chloride (NC). At one of the ASC springs, mats of Sº-rich Hydrogenobaculum-like streamers and green Cyanidia algae were also collected for comparison to the sediment. All samples were then titrated over a pH range of 3–11, and comparisons were made between the overall FG availability and the concentration of solutes bound to the samples under natural conditions. Sediments from ASC springs were composed of hydrous ferric oxides (HFO) that displayed surface FGs typical of synthetic HFO, while sediments from the NC spring were characterized by a lower functional group density, reflected by decreased excess charge over the titration range (i.e., lower surface reactivity). The latter also showed a lower apparent point of zero charge (PZC), likely due the presence of silica (up to 78 wt. %) in association with HFO. Variations in the overall HFO surface charge are manifest in the quantities and types of solutes complexed; the NC sediments bound more cations, while the ASC sediments retained significantly more arsenic, presumably in the form of arsenate (H2AsO4−). When the microbial biomass samples were analyzed, FG concentrations summed over the titratable range were found to be an order of magnitude lower for the Sº-rich mats, relative to the algal and HFO samples that displayed similar FG concentrations on a dry weight basis. A diffuse-layer surface complexation model was employed to further illustrate the importance of surface chemical parameters on adsorption reactions in complex natural systems. [ABSTRACT FROM AUTHOR]

Chemolithotrophic micro-organisms are important primary producers in high-temperature geothermal environments and may catalyse a number of different energetically favourable redox reactions as a primary energy source. Analysis of geochemical constituents followed by chemical speciation and subsequent calculation of reaction free energies (Δ Grxn) is a useful tool for evaluating the thermodynamic favourability and potential energy available for microbial metabolism. The primary goal of this study was to examine relationships among geochemical gradients and microbial population distribution, and to evaluate the utility of energetic approaches for predicting microbial metabolism from free-energy calculations, utilizing as examples, several geothermal habitats in Yellowstone National Park where thorough geochemical and phylogenetic analyses have been performed. Acidic (pH ∼ 3) and near-neutral (pH ∼ 6–7) geothermal springs were chosen for their range in geochemical properties. Aqueous and solid phase samples obtained from the source pools and the outflow channels of each spring were characterized for all major chemical constituents using laboratory and field methods to accurately measure the concentrations of predominant oxidized and reduced species. Reaction free energies (Δ Grxn) for 33 oxidation–reduction reactions potentially important to chemolithotrophic micro-organisms were calculated at relevant spring temperatures after calculating ion activities using an aqueous equilibrium model. Free-energy values exhibit significant variation among sites for reactions with pH dependence. For example, free-energy values for reactions involving Fe3+ are especially variable across sites due in large part to the pH dependence of Fe3+ activity, and exhibit changes of up to 40 kJ mol−1 electron from acidic to near neutral geothermal springs. Many of the detected 16S rRNA gene sequences represent organisms whose metabolisms are consistent with exergonic processes. However, sensitivity analyses demonstrated that reaction free energies do not generally represent the steep gradients in local geochemical conditions resulting from air–water gas exchange and solid phase deposition that are important in defining microbial habitats and 16S rRNA gene sequence distribution within geothermal outflow channels. [ABSTRACT FROM AUTHOR]

Accurate assessment of the fate of contaminants in soil relies on precise estimation of solute transport parameters under field conditions. Traditionally, transport parameters are estimated from measured solute transport data using the least-squares optimization (LSO) technique or the method of moments (MOM). Considerable mismatch between the parameters estimated by these two methods has been reported in the solute transport literature. In this study, the MOM and LSO approaches were examined for estimating pore water velocity (v) and dispersion coefficient (D) from 85 laboratory- and field-measured breakthrough curves (BTCs). The two methods yielded similar estimates of v and D for BTCs with 100% mass recovery. They yielded similar estimates of v for BTCs with incomplete mass recovery. However, estimates of D obtained by the MOM departed significantly from those estimated using LSO for STCs with incomplete mass recovery. Analyses of truncated BTCs showed that 91% mass recovery resulted in errors of 138 and 57% in D values estimated by the MOM for repacked and undisturbed soil columns, respectively. Corresponding errors in estimated D values were below 5% for the LSO approach. Although it may be possible to normalize or extrapolate the BTC using its zeroth experimental moment to ensure 100% mass recovery, the use of either LSO or MOM would yield a different set of parameters representing a new set of experimental conditions and, therefore, would lead to further complications in obtaining a unique set of transport parameters. This suggests that where the MOM is indispensable, 100% experimental mass balance should be ensured. [ABSTRACT FROM AUTHOR]

The source waters of acid-sulphate-chloride (ASC) geothermal springs located in Norris Geyser Basin, Yellowstone National Park contain several reduced chemical species, including H2, H2S, As(III), and Fe(II), which may serve as electron donors driving chemolithotrophic metabolism. Microorganisms thriving in these environments must also cope with high temperatures, low pH (∼3), and high concentrations of sulphide, As(III), and boron. The goal of the current study was to correlate the temporal and spatial distribution of bacterial and archaeal populations with changes in temperature and geochemical energy gradients occurring throughout a newly formed (redirected) outflow channel of an ASC spring. A suite of complimentary analyses including aqueous geochemistry, microscopy, solid phase identification, and 16S rDNA sequence distribution were used to correlate the appearance of specific microbial populations with biogeochemical processes mediating S, Fe, and As cycling and subsequent biomineralization of As(V)-rich hydrous ferric oxide (HFO) mats. Rapid As(III) oxidation (maximum first order rate constants ranged from 4 to 5 min−1, t1/2 = 0.17 − 0.14 min) was correlated with the appearance ofHydrogenobaculumandThiomonas–like populations, whereas the biogenesis of As(V)-rich HFO microbial mats (mole ratios of As:Fe∼0.7) was correlated with the appearance ofMetallosphaera,Acidimicrobium, andThiomonas–like populations. Several 16S sequences detected near the source were closely related to sequences of chemolithotrophic hyperthermophilic populations includingStygiolobusandHydrogenobaculumorganisms that are known H2 oxidizers. The use of H2, reduced S(–II,0), Fe(II) and perhaps As(III) by different organisms represented throughout the outflow channel was supported by thermodynamic calculations, confirming highly exergonic redox couples with these electron donors. Results from this work demonstrated that chemical energy gradients play an important role in establishing distinct community structure as a function of distance from geothermal spring discharge. [ABSTRACT FROM AUTHOR]

The influence of a nonionic (alcohol ethoxylate) surfactant (Witconol SN70) on biodegradation of phenanthrene and hexadecane (nonaqueous-phase liquid) in soil was studied in batch and transport systems. Simultaneous enhancement of phenanthrene and hexadecane degradation was noted at surfactant doses resulting in aqueous-phase surfactant concentrations below the critical micelle concentration (CMC). Conversely,degradation rates of both compounds declined to essentially zero at supra-CMC doses, suggesting that distinct mechanisms of inhibition and enhancement were operating depending on the effective surfactant concentration (i.e., accounting for surfactant sorption, log KD = 2.2 L/kg). Surfactant doses resulting in enhanced degradation correlated with enhanced gross microbial activity as determined using total CO2 evolution rates. Supra-CMC doses that resulted in inhibited degradation did not suppress gross microbial activity. Furthermore, measurements of phenanthrene solubilization and surface tension indicated that phenanthrene was solubilized at supra-CMC levelsof surfactant. Mechanisms of inhibition of phenanthrene and hexadecane degradation at supra-CMC surfactant concentrations may include changes in interfacial chemistry and subsequent mass transfer processes due to sorbed surfactant, reduced bioavailability of micelle-bound phenanthrene and hexadecane, or inhibition of specific members of the microbial community responsible for hydrophobic organic compound degradation. [ABSTRACT FROM AUTHOR]