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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A strictly anaerobic thiosulfate-reducing bacterium was isolated from a corroding offshore oil well in Congo and was designated strain SEBR 4207T. Pure culture of the strain induced a very active pitting corrosion of mild steel, with penetration rates of up to 4 mm per year. This constitutes the first experimental evidence of the involvement of thiosulfate reduction in microbial corrosion of steel. Strain SEBR 4207T cells were vibrios (3 to 5 by 1 pm), stained gram negative, and possessed lateral flagella. Spores were not detected. Optimum growth occurred in the presence of 3% NaCl at pH 7.0 and 42°C. Strain SEBR 4207T utilized peptides and amino acids, but not sugars or fatty acids. It fermented serine, histidine, and Casamino Acids, whereas arginine, glutamate, leucine, isoleucine, alanine, valine, methionine, and asparagine were only used in the presence of thiosulfate. Peptides were fermented to acetate, isobutyrate, isovalerate, 2-methylbutyrate, H,, and CO,. The addition of either thiosulfate or sulfur but not sulfate increased peptide utilization, growth rate, and biomass; during growth, H,S was produced and a concomitant decrease in H, was observed. The addition of either thiosulfate or sulfur also reversed H, inhibition. 16s rRNA sequence analysis indicates that strain SEBR 4207T is distantly related to members of the genus Thermoanuerobacter (83% similarity). Because the phenotypic and phylogenetic characteristics cannot be assigned to any described genus, strain SEBR 4207T is designated as a new species of a new genus, Dethiosulfovibrio peptidovorans gen. nov., sp. nov. Strain SEBR 4207T has been deposited in the Deutsche Sammlung von Mikroorganismen und zellkulturen GmbH (= DSM 11002).In 1989, Elf Congo experienced corrosion of the first 5 km of a 23-km main subsea pipeline that transported sour oil (i.e., H,S-containing petroleum) produced from the Emeraude oil field. The corroded segment was replaced, but it corroded again a year later. The whole line was then replaced and operated under a specifically designed biocide treatment regimen. The preliminary examination of the corroded iron showed that the breakthrough was due to bacterial pitting corrosion, with an unusually high penetration rate of about 1 cm per year. Chemical analysis of the pipeline water revealed the presence of up to 0.5 mM thiosulfate. It is likely that the thiosulfate was produced as a result of oxidation of the H,S naturally present in the oil field ecosystem by oxygen that is introduced in the pipelines during processing (10, 15, 22). The corrosion of pipelines was suspected to be due not only to sulfate but also to thiosulfate reduction by sulfate-reducing bacteria (SRB), because computer modeling had shown that thiosulfate reduction could induce the pitting corrosion of steel at higher rates than sulfate reduction (13).Since the pipeline was under a biocide treatment regimen during our microbiological investigations, the production fluids from several wellheads upstream of the line were collected and analyzed. Besides diffe...

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thermophilic, glucose-fermenting, strictly anaerobic, rod-shaped bacterium, strain SEBR 6459T (T = type strain), was isolated from an African oil-producing well. This organism was identified as a member of the genus Thennotoga on the basis of the presence of the typical outer sheath-like structure (toga) and 16s rRNA signature sequences and its ability to grow on carbohydrates (glucose, arabinose, fructose, lactose, maltose, and xylose). Major differences in its 16s rRNA gene sequence, its lower optimum temperature for growth (66"C), its sodium chloride range for growth (0 to 2.8%), its lack of lactate as an end product from glucose fermentation, and its peritrichous flagella indicate that strain SEBR 6459T is not similar to the three previously described Thennotoga species. Furthermore, this organism does not belong to any of the other genera related to the order Thermotogales that have been described. On the basis of these findings, we propose that this strain should be described as a new species, Thermotoga ewi. The type strain of T. e@i is SEBR 6459 (= DSM 9442).The order Thermotogales currently comprises three genera, TheTotoga (17), Thermosipho (18), and Fervidobacterium (19, 35). All of the species belonging to these genera are rod shaped and have a characteristic outer sheath-like structure which can be observed under in situ conditions (34). Members of the recently described genera Geotoga and Petrotoga (9) also possess this morphological feature and, as determined by a 16s rRNA sequence analysis, are distantly related to members of the Thermotogales. Collectively, the five genera mentioned above represent one of the deepest phylogenetic branches in the domain Bacteria (42). These taxa can be differentiated on the basis of their optimum temperatures for growth; Thermotoga species are extreme thermophiles that have optimum temperatures for growth of around 80°C (17, 20, 21, 41), Thermosipho and Fervidobacterium species have optimum temperatures for growth of 65 to 75°C (18, 19, 35) and are regarded as thermophiles, and Geotoga and Petrotoga species are moderate thermophiles having optimum temperatures for growth of less than 60°C (9). Until recently, members of the three genera belonging to the order Therrnotogales (Therrnotoga, Therrnosipho, and Fervidobacterium) have been isolated only from volcanic aquatic environments. Different species have different sodium chloride requirements and optimum temperatures for growth. These differences reflect the restricted ecological habitats (hydrothermal marine environments, hydrothermal terrestrial environments) from which the organisms were isolated. However, Thermotoga species capable of growth at 85°C have recently been isolated from oil wells in the North Sea (39). Davey et al. (9) have also described the isolation of members of two new genera of moderate thermoanaerobes, the genera Petrotoga and Geotoga, from oil fields. These reports have extended our knowl- edge concerning the ecological habitats of these bacteria. In this paper, we describe the results...

Gram-positive spore-forming sulfate reducers and particularly members of the genus Desulfotomaculum are commonly found in the subsurface biosphere by culture based and molecular approaches. Due to their metabolic versatility and their ability to persist as endospores. Desulfotomaculum spp. are well-adapted for colonizing environments through a slow sedimentation process. Because of their ability to grow autotrophically (H2/CO2) and produce sulfide or acetate, these microorganisms may play key roles in deep lithoautotrophic microbial communities. Available data about Desulfotomaculum spp. and related species from studies carried out from deep freshwater lakes, marine sediments, oligotrophic and organic rich deep geological settings are discussed in this review.

Two irregular coccoid methanogens designated SEBR 4845T and FRlT were isolated from an oilfield in Alsace, France. Strain SEBR 4845l (T = type strain) is a hydrogenotrophic halotolerant methanogen, which grows optimally at 5 O/ O NaCl (whr) and tolerates up t o 12O/0 NaCI. It does not use methylated compounds and therefore cannot be ascribed to any of the known genera of the halophilic methylotrophic methanogens. It differs from hydrogenotrophic members of the orders Methanococcales and Methanomicrobiales in the NaCl growth range (0-12% NaCI), which is the widest reported t o date for any hydrogenotrophic methanogen. 165 rRNA gene sequence analysis indicated that strain SEBR 4845l is a novel isolate for which a new genus is proposed, Methanocalculus halotolerans gen. nov., sp. nov. (= OCM 4703 that might be indigenous to the oilfield ecosystem. Strain FRlT (= OCM 471) is a moderately halophilic methanogen which grows optimally at 10% NaCl and tolerates up t o 20% NaCI. It grows on trimethylamine and methanol as carbon and energy sources. The G+C content of its DNA is 43 mol%. It is therefore phenotypically and genotypically related t o members of the genus Methanohalophilus. This report provides evidence that methylotrophic and hydrogenotrophic, but not aceticlastic methanogens are present in a saline subsurface oilfield environment, as already observed in surface saline t o hypersaline environments.