Scholarship & Research
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Item Arsenite oxidation by a Hydrogenobaculum sp. isolated from Yellowstone National Park(Montana State University - Bozeman, College of Agriculture, 2002) Donahoe-Christiansen, JessicaItem Geochemical characterization of sulfide mineral weathering for remediation of acid producing mine wastes(Montana State University - Bozeman, College of Agriculture, 1993) Jennings, Stuart Russell; Chairperson, Graduate Committee: Douglas J. DollhopfThe generation of acid mine drainage as a consequence of sulfide mineral oxidation is a widespread source of resource degradation. The objective of this investigation was to evaluate the influence of sulfide mineral weatherability on acid generation processes. In addition to acid generation by pyrite, the weathering characteristics of common sulfide minerals was investigated and correlated to detection by acid-base account (ABA) methodologies. The influence of particle morphology, and not particle size, was found to exert the dominant control on mineral weathering processes. Massive morphology particles generated acid at a significantly greater rate than euhedral morphology samples. Acid generation was a consequence of mineral dissolution which occurred nonuniformly across the surface of minerals during oxidation. Mineral surface weathering occurred at sites of excess energy including grain edges, steps, defects, microcracks and inclusions, resulting in the formation of etch pits. Massive morphology particles exhibited the greatest density of crystalline defect, and had the greatest rate of oxidation. Sulfide minerals found to be acid generating, in addition to pyrite, include marcasite, pyrrhotite, arsenopyrite, chalcopyrite and sphalerite. Minerals containing sulfur in the atomic structure which were not acid producing include barite, anhydrite, gypsum, anglesite, jarosite, chalcocite and galena. Delineation of acid producing and nonacid producing sulfur forms by ABA extraction methods, a standard operating procedure used in the United States, was determined to be ineffective. Effective mineral classification, particle morphology identification and observation of mineral weathering processes were accomplished by scanning electron microscopy. Accurate assessment of sulfur form distribution and sulfide mineral weathering characteristics are required for effective remediation of sites impacted by mining.Item Microbial and geochemical processes controlling the oxidation and reduction of arsenic in soils(Montana State University - Bozeman, College of Agriculture, 2007) Masur, Deanne Christine; Chairperson, Graduate Committee: William P. Inskeep.Arsenic (As) is a common contaminant in soil-water systems, where it exists predominately as arsenate (AsV) or arsenite (AsIII), the latter of which is considered to be the more mobile and toxic form. The amount of arsenite or arsenate in natural water systems is influenced by geochemical conditions and the presence of As transforming microorganisms. Consequently, the goals of this study were to evaluate the effects of: (i) arsenic concentration on microbial populations responsible for As oxidation-reduction in a previously uncontaminated soil, and (ii) phosphate:arsenic ratio on the oxidation or reduction of arsenic. Laboratory column experiments were conducted to evaluate the influence of soil arsenic concentration on microbial community composition and to identify microorganisms and mechanisms responsible for As transformations occurring under aerobic conditions. Indigenous microorganisms within a previously uncontaminated agricultural soil were exposed to arsenite or arsenate at three concentrations (2, 20 and 200 mg As L-1) for approximately 30 days.Item Microbial interactions with arsenite, hydrogen and sulfide in an acid-sulfate-chloride geothermal spring(Montana State University - Bozeman, College of Agriculture, 2008) D'Imperio, Seth; Chairperson, Graduate Committee: Timothy R. McDermott.The work presented in this thesis investigated the importance of hydrogen, sulfide and arsenite in microbial community structure and function within a model Acid-Sulfate- Chloride (ASC) spring in Yellowstone National Park. Previous studies in this spring found that microbial arsenite [As(III)] oxidation is absent in regions of the spring outflow channel where H 2S exceeds ~5 microM. Ex situ assays with microbial mat samples demonstrated immediate As(III) oxidation activity when H 2S was absent or in low concentrations, suggesting the presence of functional As(III) oxidase enzymes in regions of the spring where arsenite oxidation had not been previously observed. Cultivation efforts resulted in the isolation of an As(III)-oxidizing chemolithotroph phylogenetically related to the alpha-proteobacterium Acidicaldus. H 2S concentration appeared to be the most important constraint on spatial distribution of this organism. This was verified with pure culture modeling and kinetic experiments. Additionally, a study is presented that addresses the relative importance of dissolved hydrogen and sulfide for primary production in the same spring. Throughout the outflow channel where these gases could be detected, biological H 2S consumption rates exceeded those of H2 by at least three orders of magnitude. Molecular analysis showed that Hydrogenobaculum-like organisms dominate the microbial community in this region of the spring. Culturing efforts resulted in 30 Hydrogenobaculum isolates belonging to three distinct 16S rRNA gene phylotypes. The isolates varied with respect to electron donor (H 2S, H 2) and oxygen tolerance and requirement. These metabolic physiologies are consistent with in situ geochemical conditions. An isolate representative of the dominant 16S phylotype was used as a model organism for controlled studies to determine whether an organism capable of utilizing either of these substrates demonstrated preference for H 2S or H 2, or whether either electron donor exerted regulatory effects on the other. The organism studied utilized both H 2S and H 2 simultaneously and at rates roughly comparable to those measured in the ex situ field assays. Major conclusions drawn from this study are that phylogeny cannot be relied upon to predict physiology, and that, in ASC springs, H 2S clearly dominates H 2 as an energy source, both in terms of availability and apparent consumption rates.