Publications by Colleges and Departments (MSU - Bozeman)
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/3
Browse
6 results
Search Results
Item Diversity, abundance, and potential activity of nitrifying and nitrate-reducing microbial assemblages in a subglacial ecosystem(2011-05) Boyd, Eric S.; Lange, Rachel K.; Mitchell, Andrew C.; Havig, Jeff R.; Lafreniere, M. J.; Shock, Everett L.; Peters, John W.; Skidmore, Mark L.Subglacial sediments sampled from beneath Robertson Glacier (RG), Alberta, Canada, were shown to harbor diverse assemblages of potential nitrifiers, nitrate reducers, and diazotrophs, as assessed by amoA, narG, and nifH gene biomarker diversity. Although archaeal amoA genes were detected, they were less abundant and less diverse than bacterial amoA, suggesting that bacteria are the predominant nitrifiers in RG sediments. Maximum nitrification and nitrate reduction rates in microcosms incubated at 4°C were 280 and 18.5 nmol of N per g of dry weight sediment per day, respectively, indicating the potential for these processes to occur in situ. Geochemical analyses of subglacial sediment pore waters and bulk subglacial meltwaters revealed low concentrations of inorganic and organic nitrogen compounds. These data, when coupled with a C/N atomic ratio of dissolved organic matter in subglacial pore waters of ∼210, indicate that the sediment communities are N limited. This may reflect the combined biological activities of organic N mineralization, nitrification, and nitrate reduction. Despite evidence of N limitation and the detection of nifH, we were unable to detect biological nitrogen fixation activity in subglacial sediments. Collectively, the results presented here suggest a role for nitrification and nitrate reduction in sustaining microbial life in subglacial environments. Considering that ice currently covers 11% of the terrestrial landmass and has covered significantly greater portions of Earth at times in the past, the demonstration of nitrification and nitrate reduction in subglacial environments furthers our understanding of the potential for these environments to contribute to global biogeochemical cycles on glacial-interglacial timescales.Item Influence of bedrock mineral composition on microbial diversity in a subglacial environment(2013-06) Mitchell, Andrew C.; Lafrenière, M. J.; Skidmore, Mark L.; Boyd, Eric S.Microorganisms in subglacial environments drive the chemical weathering of bedrock; however, the influence of bedrock mineralogy on the composition and activity of microbial assemblages in such environments is poorly understood. Here, using a combination of in situ mineral incubation and DNA fingerprinting techniques, we demonstrate that pyrite is the dominant mineralogical control on subglacial bacterial community structure and composition. In addition, we show that the abundance of Fe in the incubated minerals influences the development of mineral-associated biomass. The ubiquitous nature of pyrite in many common bedrock types and high SO42– concentrations in most glacial meltwaters suggest that pyrite may be a dominant lithogenic control on microbial communities in many subglacial systems. Mineral-based energy may therefore serve a fundamental role in sustaining subglacial microbial populations and enabling their persistence over glacial-interglacial time scales.Item Recrystallization inhibition in ice due to ice binding protein activity detected by nuclear magnetic resonance(2014-09) Brown, Jennifer R.; Seymour, Joseph D.; Brox, T. I.; Skidmore, Mark L.; Wang, Chen; Christner, Brent C.; Luo, B. H.; Codd, Sarah L.Liquid water present in polycrystalline ice at the interstices between ice crystals results in a network of liquid-filled veins and nodes within a solid ice matrix, making ice a low porosity porous media. Here we used nuclear magnetic resonance (NMR) relaxation and time dependent self-diffusion measurements developed for porous media applications to monitor three dimensional changes to the vein network in ices with and without a bacterial ice binding protein (IBP). Shorter effective diffusion distances were detected as a function of increased irreversible ice binding activity, indicating inhibition of ice recrystallization and persistent small crystal structure. The modification of ice structure by the IBP demonstrates a potential mechanism for the microorganism to enhance survivability in ice. These results highlight the potential of NMR techniques in evaluation of the impact of IBPs on vein network structure and recrystallization processes; information useful for continued development of ice-interacting proteins for biotechnology applications.Item Magnetic resonance measurements of flow-path enhancement during supercritical CO2 injection in sandstone and carbonate rock cores(2014-10) Vogt, Sarah J.; Shaw, Colin A.; Maneval, James E.; Brox, Timothy I.; Skidmore, Mark L.; Codd, Sarah L.; Seymour, Joseph D.Sandstone and carbonate core samples were challenged with a two-phase supercritical CO2 and brine mixture to investigate the effects of chemical processes on the physical properties of these rocks during injection of CO2. The experiments were monitored in real-time for pressure, temperature, and volumetric rate discharge. Pore geometry and connectivity were characterized before and after each experimental challenge using magnetic resonance (MR) imaging and two-dimensional MR relaxation correlations. Quartz arenite sandstone cores were largely unaffected by the challenge with no measurable change in effective permeability at moderate and high temperatures (~50 °C and ~95 °C) or brine concentrations (~1 g/L and ~10 g/L). In contrast, a carbonate core sample showed evidence of significant dissolution leading to a six-fold increase in effective permeability. MR images and relaxation measurements revealed a marked increase in the volume and connectivity of pre-existing pore networks in the carbonate core. We infer that the increase in permeability in the carbonate core was enhanced by focused dissolution in the existing pore and fracture networks that enhanced fast-flow paths through the core.Item Aerobic and Anaerobic Thiosulfate Oxidation by a Cold-Adapted, Subglacial Chemoautotroph(2015-12) Harrold, Zoe R.; Skidmore, Mark L.; Hamilton, Trinity L.; Desch, Elizabeth; Kirina, Amada; van Gelder, Will; Glover, Kevin; Roden, Eric E.; Boyd, Eric S.Geochemical data indicate that protons released during pyrite (FeS2) oxidation are important drivers of mineral weathering in oxic and anoxic zones of many aquatic environments including those beneath glaciers. Oxidation of FeS2 under oxic, circumneutral conditions proceeds through the metastable intermediate thiosulfate (S2O32-), which represents an electron donor capable of supporting microbial metabolism. Subglacial meltwaters sampled from Robertson Glacier (RG), Canada over a seasonal melt cycle reveal concentrations of S2O32- that are typically below detection despite the presence of available pyrite and several orders of magnitude higher concentrations of the FeS2 oxidation product sulfate (SO42-). Here we report the physiological and genomic characterization of the chemolithoautotrophic facultative anaerobe Thiobacillus sp. RG5 isolated from the subglacial environment at RG. The RG5 genome encodes pathways for the complete oxidation of S2O32-, CO2 fixation, and aerobic and anaerobic respiration with nitrite or nitrate. Growth experiments indicate that the energy required to synthesize a cell under oxygen or nitrate reducing conditions with S2O32- as electron donor was lower at 5.1 °C than 14.4 °C, indicating that this organism is cold-adapted. RG sediment-associated soxB transcripts, which encode a component of the S2O32--oxidizing complex, were closely affiliated to soxB from RG5. Collectively, these results suggest an active sulfur cycle in the subglacial environment at RG mediated in part by populations closely affiliated with RG5. Microbial consumption of S2O32- by RG5-like populations may accelerate abiotic FeS2 oxidation thereby enhancing mineral weathering in the subglacial environment.Item Chemolithotrophic primary production in a subglacial ecosystem(2014-10) Boyd, Eric S.; Hamilton, Trinity L.; Havig, Jeff R.; Skidmore, Mark L.; Shock, Everett L.Glacial comminution of bedrock generates fresh mineral surfaces capable of sustaining chemotrophic microbial communities under the dark conditions that pervade subglacial habitats. Geochemical and isotopic evidence suggests that pyrite oxidation is a dominant weathering process generating protons that drive mineral dissolution in many subglacial systems. Here, we provide evidence correlating pyrite oxidation with chemosynthetic primary productivity and carbonate dissolution in subglacial sediments sampled from Robertson Glacier (RG), Alberta, Canada. Quantification and sequencing of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) transcripts suggest that populations closely affiliated with Sideroxydans lithotrophicus, an iron sulfide-oxidizing autotrophic bacterium, are abundant constituents of microbial communities at RG. Microcosm experiments indicate sulfate production during biological assimilation of radiolabeled bicarbonate. Geochemical analyses of subglacial meltwater indicate that increases in sulfate levels are associated with increased calcite and dolomite dissolution. Collectively, these data suggest a role for biological pyrite oxidation in driving primary productivity and mineral dissolution in a subglacial environment and provide the first rate estimate for bicarbonate assimilation in these ecosystems. Evidence for lithotrophic primary production in this contemporary subglacial environment provides a plausible mechanism to explain how subglacial communities could be sustained in near-isolation from the atmosphere during glacial-interglacial cycles.