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    EngD thesis describing experiments carried out using a variety of sandstones. This thesis investigates the microbial response to 10 ppm oxygen and 100ppm oxygen in experiments representing deep saline aquifer conditions. All experiments were conducted using sandstone, artificial groundwater and a microbial community designed to represent conditions found within deep saline aquifers. A microbial community, containing sulphate reducing bacteria, was isolated and identified from sandstone samples and then used in the experiments. The experiments were batch microcosms, a high pressure bioreactor and column flow experiments. Analyses of these experiments were conducted through gas analysis, water chemistry and DNA analysis from microbial communities.

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    Pyrite samples from selected sedimentary organic-rich formations or associated igneous and metamorphic rocks were analysed by conventional S isotopic analysis. Pyrites were measured in order to provide insights into their origin. Light and variable S isotope compositions in pyrite have been used to infer the influence of sulphate-reducing bacteria (and subsequent Se precipitation by sulphate-reducing microbes), whereas heavier S isotope compositions indicate a non-biological origin (i.e. physical and chemical diagenesis).