Reduction of uranium(VI) phosphate during growth of the thermophilic bacterium Thermoterrabacterium ferrireducens.

The thermophilic, gram-positive bacterium Thermoterrabacterium ferrireducens coupled organotrophic growth to the reduction of sparingly soluble U(VI) phosphate. X-ray powder diffraction and X-ray absorption spectroscopy analysis identified the electron acceptor in a defined medium as U(VI) phosphate [uramphite; (NH4)(UO2)(PO4) . 3H2O], while the U(IV)-containing precipitate formed during bacterial growth was identified as ningyoite [CaU(PO4)2 . H2O]. This is the first report of microbial reduction of a largely insoluble U(VI) compound.

Petrotoga olearia sp. nov. and Petrotoga sibirica sp. nov., two thermophilic bacteria isolated from a continental petroleum reservoir in Western Siberia.

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.

Isolation and characterization of Thermococcus sibiricus sp. nov. from a Western Siberia high-temperature oil reservoir.

Anaerobic organotrophic hyperthermophilic Archaea were isolated from five of eight samples from oil wells of the Samotlor oil reservoir (depth, 1,799-2,287 m; temperature, 60 degrees-84 degrees C). Three strains were isolated in pure cultures and characterized phylogenetically on the basis of comparison of the 16S rRNA gene sequences. All strains belonged to a new species of the genus Thermococcus, with Thermococcus litoralis, Thermococcus aggregans, Thermococcus fumicolans, and Thermococcus alcaliphilus being the nearest relatives (range of sequence similarity, 97.2%-98.8%). Strain MM 739 was studied in detail. The new isolate grew on peptides but not on carbohydrates. Elemental sulfur had a stimulatory effect on growth. The temperature range for growth was between 40 degrees and 88 degrees C, with the optimum at 78 degrees C; the pH range was 5.8 to 9.0, with the optimum around 7.3; and the salinity range was 0.5% to 7.0%, with the optimum at 1.8%-2.0%. The doubling time at optimal growth conditions was about 43 min. The G+C content of the DNA was 38.4 mol%. The DNA-DNA relatedness between strain MM 739 and T. litoralis was 27%; between strain MM 739 and T. aggregans, it was 22%. Based on the phenotypic and genomic differences with known Thermococcus species, the new species Thermococcus sibiricus is proposed. The isolation of a hyperthermophilic archaeum from a deep subsurface environment, significantly remote from shallow or abyssal marine hot vents, indicates the existence of a subterranean biosphere inhabited by indigenous hyperthermophilic biota.