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A new thermophilic, xylanolytic, strictly anaerobic, rod-shaped bacterium, strain SEBR 7054T, was isolated from an African oil-producing well. Based on the presence of an outer sheath (toga) and 16s rRNA sequence analysis data, this organism was identified as a member of the genus Thermotoga. Strain SEBR 7054T possessed lateral flagella, had a G+C content of 50 mol%, produced traces of ethanol ffom glucose but no lactate, and grew optimally in the presence of 0 to 0.2% NaCl at 70°C. Its phenotypic and phylogenetic characteristics clearly differed from those reported for the five previously validly described Thermotoga species. Therefore, we propose that strain SEBR 7054T is a member of a new species of the genus Thermotoga, Thermotoga hypogea sp. nov. The type strain of T. hypogea is SEBR 7054 (= DSM 11164).Members of the order Thermotogales are rod-shaped bacteria that have a characteristic outer sheathlike structure called a toga. This order includes the following five genera: Thermotoga (18,22, 23,34,44), Thermosipho (19, 37), Fewidobacterium (1, 20, 32), Geotoga, and Petrotogu (9). It represents, along with the AquiJicales, the deepest phylogenetic branch in the domain Bacteria (45). The genus Thermotoga includes all of the hyperthermophiles (optimum temperature for growth, around 80°C) of the order Thermotogales (18, 21, 22) and the thermophiles (optimum temperature for growth, 65 to 70°C) recently isolated from oil fields (23,34). Stetter et al. (39) provided evidence of the presence of Thermotoga strains in oil fields. The isolation of Thennotoga elfii and Thermotoga subterranea from such ecosystems was reported soon thereafter (23,34). In contrast to Thermotoga maritima and i%ermotoga neapolitana, T. elfii and T. subterranea were not able to grow at temperatures above 75°C and reduced thiosulfate but not sulfur, which led to speculation that thiosulfate rather than sulfur may be an important electron acceptor in oil field ecosystems (34). The presence of thiosulfate is also thought to increase biocorrosion of oil field installations (8,27). We therefore initiated intensive studies to isolate Thermotoga strains from oil field subsurface ecosystems that grow at temperatures above 80°C and use thiosulfate as an electron acceptor. Our studies have focused on xylanolytic extremophilic microorganisms since thermostable xylanases have a potential use in paper primary-pulp manufacturing (33). In this paper, we describe the first isolation from oil field water of a xylanolytic Thermotoga species able to grow at temperatures up to 90°C. The phenotypic and phylogenetic characteristics of the new strain are consistent with its placement in a new species of the genus Thermotoga, Thermotoga hypogea sp. nov. MATERIALS AND METHODSSample collection and sample source. Strain SEBR 7054= was isolated from an oil-producing well in Cameroon in central Africa. The in situ temperature was 66"C, and the concentration of sodium chloride was 12 glliter. A 1-liter sample was collected at the wellhead as described elsewhere (3), t...

Although the importance of bacterial activities in oil reservoirs was recognized a long time ago, our knowledge of the nature and diversity of bacteria growing in these ecosystems is still poor, and their metabolic activities in situ largely ignored. This paper reviews our current knowledge about these bacteria and emphasises the importance of the petrochemical and geochemical characteristics in understanding their presence in such environments.

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