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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 microns), 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 degrees 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, H2, and CO2. The addition of either thiosulfate or sulfur but not sulfate increased peptide utilization, growth rate, and biomass; during growth, H2S was produced and a concomitant decrease in H2 was observed. The addition of either thiosulfate or sulfur also reversed H2 inhibition. 16S rRNA sequence analysis indicates that strain SEBR 4207T is distantly related to members of the genus Thermoanaerobacter (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).

A strictly anaerobic, moderately halophilic, Gram-negative, non-motile rod-shaped bacterium was isolated from an oil-well head sample of an offshore Congolese oil field. The strain, designated SEBR 4224T (T = type strain), grew optimally at 42 degrees C and pH 7.0 in a complex medium containing 10% NaCl with a generation time of 2.5 h. Strain SEBR 4224T grew on a range of carbohydrates including fructose, galactose, D-glucose, maltose, D-mannose, D-ribose, sucrose, and trehalose. Yeast extract and/or bio-Trypcase was required for growth on carbohydrates and could not be replaced with amino acids and/or vitamins. The end-products from glucose fermentation were acetate, H2, and CO2. Thiosulfate and elemental sulfur were used as electron acceptors. Thiosulfate improved carbohydrate utilization and biomass yields. The G + C content of the isolate was 34 mol%. Ribosomal 16S rRNA sequence analysis showed that strain SEBR 4224T is a new member of the genus Haloanaerobium. The lack of DNA homology with H. acetoethylicum, its closest relative, as determined by DNA-DNA hybridization supports the designation of strain SEBR 4224T as a new species, Haloanaerobium congolense sp. nov. The type strain is SEBR 4224T (= DSM 11287).