Two bacterial isolates, designated S1.1 and S3.1, were recovered from oil-well produced water extracted from a deep and hot oil-well in the Thar Jath oil-field in South Sudan, and characterized. Based on their 16S rRNA gene sequences and phenotypic properties, the isolates were identified as members of the genus Thermoanaerobacter, possibly representing novel species. Both strains are strict anaerobes, grow optimally at 65 – 70°C at neutral pH and with ~0.3% NaCl, and can use various carbohydrates, proteinaceous compounds and organic acids as growth substrates. Strain S1.1 differs from strain S3.1 in its ability to grow on xylan and D-ribose, and S3.1 from S1.1 in its capacity to grow on acetate, arabinose, cellulose and lactate. Both produced acetate, ethanol, carbon dioxide and hydrogen as fermentation by-products from glucose, and growth was stimulated by thiosulphate. Strain S1.1 actively reduced Fe(III) as revealed by the formation of a dark paramagnetic precipitate and increased growth in cultures supplemented with Fe2O3. Cultures of both strains survived autoclaving at 121°C for 40 min, suggesting the formation of extremely heat-resistant endospores.
Key words: Thermoanaerobacter, oil-well, produced water, deep biosphere, petroleum microbiology, thermophiles, Thar Jath.
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