Scholarship & Research
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/1
Browse
10 results
Filters
Settings
Search Results
Item Operando optical and quantitative electrochemical studies of solid oxide fuel cell anode degradation and regeneration(Montana State University - Bozeman, College of Letters & Science, 2022) Pomeroy, Elias Deen; Chairperson, Graduate Committee: Robert Walker; This is a manuscript style paper that includes co-authored chapters.Solid Oxide Fuel Cells (SOFCs) are high temperature (600-1000 °C) devices that can generate electricity with extremely high efficiencies from a wide variety of fuels, including H 2, CH 4, Biogas, and crushed coal. Unfortunately, the SOFC anodes are highly sensitive to gas phase contaminants, including sulfur and carbon containing fuels. Sulfur is ubiquitous in all carbon containing fuels, with concentrations as low as a few parts per million to as high as 1% by mass. At all concentrations sulfur substantially decreases SOFC performance. Conventional models propose that sulfur decreases fuel cell performance by blocking anode active sites, preventing electrochemical reactions, and reducing surface area for heterogeneous catalysis. Carbon containing fuels can rapidly degrade SOFCs due to graphitic carbon formation. Graphite blocks active sites on the anode, causes damage within the anode microstructure, and removes electrocatalytic material via metal dusting. Studies presented in this work used operando optical techniques and quantitative electrochemistry to study degradation and remediation of SOFC anodes. First, since typical electrochemical techniques infer microstructural changes rather than directly measuring surface area, a traditional electrochemical technique, chronocoulometry (CC), was adapted to SOFCs for the first time to measure the electrochemically active area of the anode. This technique showed that active area is temperature dependent, and that sulfur participates in electrochemical reactions, decreasing performance with sluggish oxidation kinetics, rather than simply blocking active sites. Carbon monoxide, on the other hand, decreased the number of active sites, rather than participating in electrochemical reactions, either by blocking active sites or forming carbon. Then, a comparative study was undertaken of different methodologies of carbon remediation, comparing electrochemical oxidation, molecular oxygen, and steam as methods to remove graphite accumulated on SOFC anodes. This study found that with all methods, CO 2 played a key role in removing carbon, that both electrochemical oxidation and steam removed carbon more globally than oxygen, and that imaging the entire cell is critical for understanding the complex, spatially and temporally heterogeneous chemistry occurring across SOFC anodes. Finally, sulfur was employed to passivate SOFC anodes operating on dry methane, significantly reducing carbon formation with only slight decreases in electrochemical performance.Item Reductive dissolution of pyrite by methanogens and its physiological and ecological consequences(Montana State University - Bozeman, College of Agriculture, 2022) Payne, Devon; Chairperson, Graduate Committee: Eric Boyd; This is a manuscript style paper that includes co-authored chapters.All life requires iron and sulfur, in particular, for use in metallocofactors of enzymes that catalyze chemistry that is essential for metabolism. In anaerobic environments, iron and sulfur are typically found in their reduced forms (ferrous iron and sulfide, respectively) that will react and form insoluble iron-sulfide minerals, such as pyrite. A consequence of this is that either iron or sulfur are typically limiting in solution, raising the question as to how anaerobes acquire these essential elements under such conditions. Here, it is demonstrated that anaerobic methanogens can reduce pyrite to release iron and sulfur that are assimilated by the cells to meet biosynthetic demands. Through a combination of growth experiments, -omics analyses, and microscopy, a model for the reductive dissolution of pyrite was established. In this model, direct contact between cells and pyrite is required for mineral reduction. When in direct contact, pyrite is reduced and sulfide is released, leaving a pyrrhotite secondary mineral on the surface. Iron solubilized from pyrrhotite reacts with sulfide in the growth medium to yield aqueous iron sulfur clusters that are assimilated by cells. Cells grown on pyrite exhibit phenotypic differences in comparison to traditionally grown cells provided with ferrous iron and sulfide. At a morphological level, pyrite-grown cells were 33% smaller than traditionally grown cells and hyperaccumulated iron as an intracellular mineral. When grown under nitrogen-fixing conditions, cells grown on pyrite had higher cell densities, growth yields, and growth rates in comparison to traditionally grown cells. Molybdate transporters were down expressed in pyrite-grown, nitrogen-fixing cells relative to traditionally-grown cells, consistent with sulfide limiting molybdate availability in the latter condition. Moreover, pyrite-grown cells could fix nitrogen at ~100-fold lower molybdenum concentration than traditionally grown cells, indicating differences in molybdenum requirements based on the iron and sulfur source provided. Together, these data highlight that in contemporary anoxic environments, iron-sulfide minerals are an important and even preferred source of iron and sulfur for methanogens. These findings provide insight into how ancient methanogens could have acquired iron and sulfur on an anoxic early Earth when one or both of these elements were likely only available as metal sulfides.Item The reactive form of a C-S bond-cleaving CO 2-fixing flavoenzyme(Montana State University - Bozeman, College of Letters & Science, 2019) Mattice, Jenna Rose; Chairperson, Graduate Committee: Jennifer DuBois; Thesis includes a paper of which Jenna R. Mattice is not the main author.Atmospheric carbon dioxide (CO 2) is used as a carbon source for building biomass in plants and most engineered synthetic microbes. Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), the most abundant enzyme on earth, is used by these organisms to catalyze the first step in CO 2 fixation. 1,2 Microbial processes that also fix carbon dioxide or bicarbonate have more recently been discovered. My research focuses on a reaction catalyzed by 2-KPCC (NADPH:2-ketopropyl-coenzyme M oxidorectuase/ carboxylase), a bacterial enzyme that is part of the flavin and cysteine-disulfide containing oxidoreductase family (DSORs) which are best known for reducing metallic or disulfide substrates. 2-KPCC is unique because it breaks a comparatively strong C-S bond, leading to the generation of a reactive enolacetone intermediate which can directly attack and fix CO 2. 2-KPCC contains a phenylalanine in the place where most other DSOR members have a catalytically essential histidine. This research focuses on studying the unique reactive form of 2-KPCC in presence of an active site phenylalanine.Item Flexibility in the mineral dependent metabolism of a thermoacidophilic crenarchaeote(Montana State University - Bozeman, College of Letters & Science, 2017) Amenabar Barriuso, Maximiliano Jose; Chairperson, Graduate Committee: Eric Boyd; John W. Peters (co-chair); Everett L. Shock, Eric E. Roden, John W. Peters and Eric S. Boyd were co-authors of the article, 'Microbial substrate preference dictated by energy demand rather than supply' in the journal 'Nature geoscience' which is contained within this thesis.; Daniel R. Colman, Saroj Poudel, Eric E. Roden and Eric S. Boyd were co-authors of the article, 'Expanding anaerobic heterotrophic metabolism with hydrogen' submitted to the journal 'Environmental microbiology' which is contained within this thesis.; Eric S. Boyd was a co-author of the article, 'Flexibility in mineral dependent energy metabolism broadens the ecological niche of a thermoacidophile' submitted to the journal 'Environmental microbiology' which is contained within this thesis.This dissertation focuses on understanding the metabolic flexibility of a thermoacidophilic crenarchaeote, the mechanisms underlying its physiology, and the consequences for its ecology. Acidianus strain DS80 was isolated from an acidic spring in Yellowstone National Park (YNP) and displays versatility in energy metabolism, using soluble and insoluble substrates during chemolithoautotrophic, chemoheterotrophic, and/or chemolithoheterotrophic growth, and is widely distributed among YNP springs. This flexibility suggests that strain DS80 is of utility as a model thermoacidophile that allows investigation towards how metabolically flexible microorganisms select among available substrates and how these traits influence their natural distributions. Moreover, this plasticity allows investigation of the agreement between thermodynamic metabolic predictions and physiological measurements. Here, I showed that strain DS80 prefers growth with redox couples that provide less energy (H2/S°) when compared to other redox couples (H2/Fe3+ or S°/Fe3+). I present a bioenergetic-physiological argument for this preference, suggesting that the preferential use of substrates in metabolically versatile strains, such as strain DS80, is dictated by differences in the energy demand of electron transfer reactions rather than the energy supply. These observations may help explain why thermodynamic approaches alone are often not enough to accurately predict the distribution and activity of microorganisms in environments. I then showed that genome-guided predictions of energy and carbon metabolism of organisms may not agree with physiological observations in the laboratory, and by extension, the environment. Using a suite of physiological experiments, I provide evidence that the availability of electron acceptors influences the spectrum of potential electron donors and carbon sources that can sustain growth. Similarly, the availability of H2 enables the use of organic carbon sources in DS80 cells respiring S°, thereby expanding the ecological niche of this organism by allowing them to compete for a wider array of substrates that are available in dynamic environments. Finally, I showed that strain DS80 can use several minerals for chemolithotrophy and that the use of specific metabolisms dictates the requirement for direct access to these minerals. Taken together, the results shown here provide novel insight into the extent and mechanisms of metabolic flexibility of chemolithotrophs and the consequences for their ecology.Item Linking geochemistry with microbial community structure and function in sulfidic geothermal systems of Yellowstone National Park(Montana State University - Bozeman, College of Agriculture, 2015) Jay, Zackary James; Chairperson, Graduate Committee: William P. Inskeep; Doug B. Rusch, Susannah G. Tringe, Connor Bailey, Ryan M. Jennings and William P. Inskeep were co-authors of the article, 'Predominant acidilobus-like populations from geothermal environments in Yellowstone National Park exhibit similar metabolic potential in different hypoxic microbial communities' in the journal 'Applied and environmental microbiology' which is contained within this thesis.; Jacob P. Beam, Alice Dohnalkova, Regina Lohmayer, Brynna Bodle, Brita Planer-Friedrich, Margaret Romine and William P. Inskeep were co-authors of the article, 'Pyrobaculum yellowstonensis strain WP30 respires on elemental sulfur and/or arsenate in circumneutral sulfidic geothermal sediments of Yellowstone National Park' submitted to the journal 'Applied and environmental microbiology' which is contained within this thesis.; Doug B. Rusch, Jacob P. Beam, Mark A. Kozubal, Ryan M. Jennings and William P. Inskeep were co-authors of the article, 'The distribution, diversity and function of predominant Thermoproteales phylotypes in Yellowstone National Park' submitted to the journal 'ISME J' which is contained within this thesis.Members of the archaeal phylum Crenarchaeota are often associated with microbial communities in high-temperature (> 70 °C) geothermal springs. Environmental genome sequencing (metagenomics) has revealed that populations of Sulfolobales, Desulfurococcales, and Thermoproteales are abundant in hypoxic elemental sulfur sediments of Yellowstone National Park (YNP) and possess enzyme complexes that are implicated in the cycling of carbon, sulfur, and arsenic. Therefore, the primary objectives of this work were to (i) identify the abundant Desulfurococcales and Thermoproteales sequences in these habitats, (ii) characterize the growth and curate the genome of the first Thermoproteales representative isolated from YNP (Pyrobaculum yellowstonensis strain WP30), and (iii) establish a linkage between geochemistry and microbial community structure and function by identifying key proteins that are important to these populations in situ. The primary Desulfurococcales populations were related to Acidilobus spp. and exhibited similar metabolic potential in near-neutral (pH 4 - 6) hypoxic elemental sulfur sediments and acidic (pH ~3) iron oxide mats. These populations are primarily anaerobic heterotrophs that ferment complex organic carbon and are auxotrophic with regards to numerous vitamins and cofactors. These organisms are often found together with members of the Thermoproteales, which are widely distributed in elemental sulfur sediments, acidic iron oxide mats, and streamer communities. P. yellowstonensis strain WP30 was obtained from a hypoxic elemental sulfur sediment habitat with high concentrations of arsenic. This organism was shown to reduce elemental sulfur and/or arsenate in the presence of yeast extract. The complete genome of str. WP30 contained numerous dimethylsulfoxide molybopterin (DMSO-MPT) proteins, which are inovolved in redox reactions of inorganic constituents (i.e. sulfur and arsenic), and genomic comparisons revealed that this organism is closely related to native Pyrobaculum populations. The distribution of Thermoproteales populations was correlated with pH, while the presence of respiratory complexes (terminal oxidases, DMSO-MPT, and dissimilatory sulfate reductases) was correlated with the presence of key electron donors and acceptors. Intron sequences identified in Thermoproteales 16S rRNA genes and were shown in silico to prevent the binding of 'universal' primers that are often used in environmental surveys. These metagenomic, microbiological, and geochemical studies have advanced the understanding of Crenarchaeota diversity and function in YNP.Item Band applications of elemental sulfur inoculated with Thiobacillus thioparus to enhance nutrient availability(Montana State University - Bozeman, College of Agriculture, 1987) DeLuca, Thomas HenryItem Chemistry and mineralogy of four acid sulfate soils from Montana, North Dakota, and Wyoming(Montana State University - Bozeman, College of Agriculture, 1989) Blodgett, Stephen DanielItem The development and characterization of the phytoavailability soil test for potassium, sulfur, and phosphorus(Montana State University - Bozeman, College of Agriculture, 1989) Georgitis, Stuart JamesItem Effect of nitrogen and sulfur fertilization on forages in the Gallatin Valley of Montana(Montana State University - Bozeman, College of Agriculture, 1982) Gavlak, Raymond GeorgeItem Sulfur poisoning of methanation catalysts : pulse poisoning with hydrogen sulfide(Montana State University - Bozeman, College of Engineering, 1983) Swanberg, David Jonathon