Thermotoga petrophila sp nov and Thermotoga naphthophila sp nov., two hyperthermophilic bacteria from the Kubiki oil reservoir in Niigata, Japan

Two hyperthermophilic bacteria, strains RKU-1(T) and RKU-10(T), which grew optimally at 80 degreesC, were isolated from the production fluid of the Kubiki oil reservoir in Niigata, Japan. They were strictly anaerobic, rod-shaped fermentative heterotrophs. Based on the presence of an outer sheath-like structure (toga) and 16S rDNA sequences, they were shown to belong to the genus Thermotoga. Cells of strain RKU-1(T) were 2-7 mum by 0.7-1.0 mum, with flagella. They grew at 47-88 degreesC on yeast extract, peptone, glucose, fructose, ribose, arabinose, sucrose, lactose, maltose, starch and cellulose as sole carbon sources. Cells of strain RKU-10(T) were 2-7 mum by 0.8-1.2 mum, with flagella. They grew at 48-86 degreesC on yeast extract, peptone, glucose, galactose, fructose, mannitol, ribose, arabinose, sucrose, lactose, maltose and starch as sole carbon sources. While strains RKU-1(T) and RKU-10(T) reduced elemental sulfur to hydrogen sulfide, their final cell yields and specific growth rates decreased in the presence of elemental sulfur. Thiosulfate also inhibited growth of strain RKU-1(T) but not strain RKU-10(T). The G+C contents of the DNA from strains RKU-1(T) and RKU-10(T) were 46.8 and 46.1 mol%. Phenotypic characteristics and 16S rDNA sequences of the isolates were similar to those of Thermotoga maritima and Thermotoga neapolitana, both being hyperthermophilic bacteria isolated from hydrothermal fields. However, the isolates differed from these species in their minimum growth temperatures, utilization of some sugars, sensitivity to rifampicin and the effects of elemental sulfur and thiosulfate on growth. The low levels (less than 31%) of DNA reassociation between any two of these hyperthermophilic Thermotoga strains indicated that the isolates were novel species. Analysis of the gyrB gene sequences supported the view that the isolates were genotypically different from these reference species. The isolates were named Thermotoga petrophila sp. nov., with type strain RKU-1(T) (= DSM 13995(T) = JCM 10881(T)), and Thermotoga naphthophila sp. nov., with type strain RKU-10(T) (= DSM 13996(T) = JCM 10882(T)).