Publications by Colleges and Departments (MSU - Bozeman)
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Item Geographic, seasonal, and precipitation chemistry influence on the abundance and activity of biological ice nucleators in rain and snow(2008-11) Christner, Brent C.; Cai, Rongman; Morris, Cindy E.; McCarter, Kevin S.; Foreman, Christine M.; Skidmore, Mark L.; Montross, Scott N.; Sands, David C.Biological ice nucleators (IN) function as catalysts for freezing at relatively warm temperatures (warmer than −10 °C). We examined the concentration (per volume of liquid) and nature of IN in precipitation collected from Montana and Louisiana, the Alps and Pyrenees (France), Ross Island (Antarctica), and Yukon (Canada). The temperature of detectable ice-nucleating activity for more than half of the samples was ≥ −5 °C based on immersion freezing testing. Digestion of the samples with lysozyme (i.e., to hydrolyze bacterial cell walls) led to reductions in the frequency of freezing (0–100%); heat treatment greatly reduced (95% average) or completely eliminated ice nucleation at the measured conditions in every sample. These behaviors were consistent with the activity being bacterial and/or proteinaceous in origin. Statistical analysis revealed seasonal similarities between warm-temperature ice-nucleating activities in snow samples collected over 7 months in Montana. Multiple regression was used to construct models with biogeochemical data [major ions, total organic carbon (TOC), particle, and cell concentration] that were accurate in predicting the concentration of microbial cells and biological IN in precipitation based on the concentration of TOC, Ca2+, and NH4+, or TOC, cells, Ca2+, NH4+, K+, PO43−, SO42−, Cl−, and HCO3−. Our results indicate that biological IN are ubiquitous in precipitation and that for some geographic locations the activity and concentration of these particles is related to the season and precipitation chemistry. Thus, our research suggests that biological IN are widespread in the atmosphere and may affect meteorological processes that lead to precipitation.Item Bacteria in subglacial environments(2008) Christner, Brent C.; Skidmore, Mark L.; Priscu, John C.; Tranter, Martyn; Foreman, Christine M.Glaciers exist where the annual temperature remains cold enough to allow snowfall to accumulate for an extended period of time and where conditions allow subsequent metamorphosis to ice. Glacial ice forms expansive continental ice sheets in the polar regions, (e.g., in Antarctica and Greenland), and at lower latitudes, ice fields (valley or alpine glaciers) and ice caps (if a volcano or mountain range is completely glaciated) exist globally at high altitude. Temperate glaciers comprise <4% of the glacial ice on the planet, but are important freshwater reservoirs and are often the sources for major rivers vital for irrigation, industry, and providing millions of people with drinking water. The Greenland and Antarctic ice sheets currently cover ~10% of the terrestrial surface (>1.5×107 km2) and contain ~75% of the freshwater on Earth (Paterson 1994). The Antarctic ice sheet alone contains ~90% of the planet's ice and, if melted, would result in a sea level rise of ~65 m (The National Snow and Ice Data Center; http://nsidc.org/).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.