A hyperthermophilic sulfate reducer, strain 7324, was isolated from hot (75°C) oil field waters from an oil production platform in the Norwegian sector of the North Sea. It was enriched on a complex medium and isolated on lactate with sulfate. The cells were nonmotile, irregular coccoid to disc shaped, and 0.3 to 1.0 μm wide. The temperature for growth was between 60 and 85°C with an optimum of 76°C. Lactate, pyruvate, and valerate plus H2 were utilized as carbon and energy sources with sulfate as electron acceptor. Lactate was completely oxidized to CO2. The cells contained an active carbon monoxide dehydrogenase but no 2-oxoglutarate dehydrogenase activity, indicating that lactate was oxidized to CO2 via the acetyl coenzyme A/carbon monoxide dehydrogenase pathway. The cells produced small amounts of methane simultaneously with sulfate reduction. F420 was detected in the cells which showed a blue-green fluorescence at 420 nm. On the basis of morphological, physiological, and serological features, the isolate was classified as an Archaeoglobus sp. Strain 7324 showed 100% DNA-DNA homology with A. fulgidus Z, indicating that it belongs to the species A. fulgidus. Archaeoglobus sp. has been selectively enriched and immunomagnetically captured from oil field waters from three different platforms in the North Sea. Our results show that strain 7324 may grow in oil reservoirs at 70 to 85°C and contribute to hydrogen sulfide formation in this environment.
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