Browsing by Subject "geobiology"

Now showing 1 - 3 of 3
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    Biogeochemical Factors Impacting the Habitability of the Soudan Formation: Iron and Sulfur Cycling, Biofilms, and Fracture Surface Alteration
    (2023-12) Schuler, Christopher
    Fractured-rock networks in the continental crust constitute one of the largest microbial habitats on earth. These environments are generally low in oxygen and are cut off from surface-derived carbon; bacteria and archaea instead derive their energy from the oxidation and reduction of inorganic substrates sourced from rock-water interactions. Because of this, biogeochemical cycles governed by local mineralogy can have a major impact on the distribution and characteristics of subsurface organisms. Life in these environments mainly consists of surface-attached and biofilm-hosted microbial communities, and the impact that fine-scale mineralogical variation has on their abundance and composition is not yet fully understood. This dissertation characterizes the rock and groundwater chemistry of the Soudan formation, an Archean banded iron formation in northeastern Minnesota, to better understand both the rock-water interactions driving crustal biogeochemical cycling and the interactions between microbes and minerals in the subsurface. The differing rock and water chemistries of boreholes drilled into this formation are compared both to each other and to other sites where deep subsurface life has been studied. Mineral precipitate forming within these boreholes is collected and characterized; biofilm on the mineral precipitate surface is examined as well. Finally, thin sections are prepared from drill cores to identify both the bulk mineralogy of the Soudan formation and the alteration phases forming at fracture edges. The Soudan formation was found to contain isolated groundwaters with high Ca-Na-Cl salinity. Both the subsurface microbial community and hematite in the banded iron formation drive an active, cryptic S cycle with the potential to support both sulfur oxidizing and sulfate reducing microbes. In some fractures within the formation, Fe and S reduction lead to the precipitation of the iron sulfide minerals mackinawite and greigite. The mineral precipitates become covered in dense biofilms hosting morphologically diverse microbial communities. However, the extent of precipitate formation differs from borehole to borehole, showing that subsurface activity can differ extensively from fracture to fracture even within a geographically confined area. Fracture edges accessed via drill cores show signs of both the high-temperature deposition of chlorite minerals and the low-temperature precipitation of calcite. Carbonate minerals are undersaturated in most water samples from Soudan, though, suggesting that water chemistry at the fracture surface differs from that measured in well-mixed borehole effluent. Overall, this work describes Fe and S cycling in the Soudan formation in detail and illustrates that understanding fracture mineralogy at the micron scale is necessary to get a full picture of subsurface ecosystems.
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    Calcium Phosphate Mineralization as a Nexus of Geosphere–Biosphere interactions
    (2017-10) Crosby, Chris
    There is arguably no more direct example of the dynamic relationship between the geosphere and the biosphere than the element phosphorus. Originally sourced from the rocky material of Earth, phosphorus enters the biosphere as the highly charged phosphate ion that is incorporated into every cell of every organism, and eventually returns to the geosphere in sedimentary phosphate rock. Although both igneous and sedimentary phosphate rock is mined for use in fertilizers, mineable phosphate rock is not evenly distributed across the Earth which imbues this vital resource with global economic significance and makes it an important issue in international relations, with wide-ranging implications for global human population growth trends. Phosphorus-related research is conducted in a wide variety of fields, including the medical and dental sciences, environmental and agricultural sciences, wastewater treatment technology, geology and mining. Indeed, there are many angles from which to explore the function and importance of phosphorus. In this thesis, I focus on some of the aspects of the phosphorus-related interplay between the geosphere and the biosphere through both 1) the ancient rock record, through analysis and interpretation of ~2 billion year old phosphate rock carrying an imprint of the biologically influenced cycling of phosphorus and 2) the modern, through laboratory experiments designed to elucidate details of the nucleation and precipitation of solid calcium-phosphate minerals in proximity with biological material. My work in the rock record carries significance for our understanding of the co-evolution of a relatively young, only recently oxygenated Earth and coeval life as it evolved to adapt to this changing environment. In addressing challenges inherent in determining bona fide biogenicity of putative microfossils, this work is also relevant to the field of micropaleontology. Finally, I offer a newly developed apparatus and protocol for use in the experimental examination of mineral precipitation over time and in the context of polymeric matrices such as those implicated in both biologically directed mineralization and biologically influenced precipitation of calcium-phosphate minerals and their precursors.
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    Hitching a ride: A gastropod-associated microbiome community at a Hydrate Ride methane seep and impacts on local biogeochemical cycling
    (2022-10) Shaner, Sydney
    Exploration of cold seeps from geological, chemical, and biological perspectives has grown exponentially in recent decades since the first discovery of cold seeps in the 1980s. Symbiotic relationships, often rooted in geochemistry of the environment, have proven to be ubiquitous at cold seeps. However, our understanding of symbiotic relationships at extreme environments is limited. In this thesis, we first review two kinds of cold seep systems—gas hydrate-forming seeps, using Hydrate Ridge as an example, and brine-influenced seeps, with a focus on the Gulf of Mexico—from geological, microbiological, and biogeochemical perspectives. We then report on the composition of microbial communities associated with provannid gastropods as characterized using 16S rRNA gene amplicon and clone libraries as well as Fluorescence In Situ Hybridization. The gastropod shells, collected from seeps at Hydrate Ridge and the Gulf of Mexico are covered with filamentous epibionts on their shells. Large filamentous epibionts were identified as Candidatus Marithrix, Thiomargarita nelsonii, and a previously undescribed Chloroflexi. Our analysis of three incomplete Chloroflexi’s genomes leads us to hypothesize that the Chloroflexi is an acetogen. Environmental samples from a previous sample revealed that the gastropod-associated community differed from the surrounding microbial communities, implying a selection mechanism for gastropod habitation and that the gastropod shell potentially serves as a unique niche. The diverse community of microbes on the shell of these seep-dwelling gastropods may represent a symbiotic relationship made possible by the gastropods motility that provides the attached microbial community with essential metabolites, while the attached community may serve the gastropod by providing it with a source of nutrition, and potentially detoxifying hydrogen sulfide.