Strictly anaerobic, thermophilic bacteria (strains SL24T, SL25T, SL27, SL29 and SL32) were isolated from a deep, continental oil reservoir in Western Siberia (Russia). These motile, rod-shaped organisms were surrounded by a sheath-like structure, a feature characteristic of the Thermotogales. On the basis of partial 16S rDNA sequences (500 nucleotides), strains SL25T, SL27, SL29 and SL32 were identical. Therefore, only strains SL24T and SL25T were studied in detail. The optimum temperature for growth of both strains was 55 degrees C. Their optimum pH for growth was 7.5 and their optimum NaCl concentration was between 20 and 30 g l(-1). The novel isolates reduced elemental sulfur and cystine, but not thiosulfate or sulfate, to hydrogen sulfide. The G+C contents of the genomic DNA of strains SL24T and SL25T were respectively 35 and 33 mol%. Phylogenetically, both strains are most closely related to Petrotoga miotherma, there being 98.9-99.4% similarity between their 16S rDNA sequences. Phenotypic properties and DNA-DNA hybridization experiments indicate that the strains belong to two novel species, for which the names Petrotoga olearia (type strain SL24T = DSM 13574T = JCM 11234T) and Petrotoga sibirica (type strain SL25T= DSM 13575T = JCM 11235T) are proposed.


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