Fervidobacterium riparium sp. nov., a thermophilic anaerobic cellulolytic bacterium isolated from a hot spring

A novel obligately anaerobic, extremely thermophilic, organotrophic bacterium, strain 1445t ^T, was isolated from a hot spring on Kunashir Island (Kuril Islands, Russia). Cells were motile rods (0.4- 0.5 × 1.0-3.0 μm). The temperature range for growth at pH 7.8 was 46-80 °C, with optimum growth at 65 °C. The pH range for growth at 65 °C was pH 5.7-9.0, with optimum growth at pH 7.8. Growth was not observed at or below 40 °C, at or above 84 °C, at or below pH 5.4 or at or above pH 9.5. The isolate degraded a wide range of substrates including starch, cellulose and cellulose derivatives. Elemental sulfur stimulated growth, but sodium sulfate, sulfite and thiosulfate did not. DNA G+C content was 31 mol%. Phylogenetic analysis of 16S rRNA gene sequences showed that strain 1445t ^T belonged to the genus Fervidobacterium. 16S rRNA gene sequence similarities with strains of other species of the genus Fervidobacterium were 94.9-98.3%; the type strain of Fervidobacterium gondwanense was the closest relative of strain 1445t ^T. DNA- DNA hybridization of strain 1445t ^T and F. gondwanense AB39 ^T revealed a relatedness value of 20%. Based on phylogenetic data and physiological properties of the isolate, a novel species, designated Fervidobacterium riparium sp. nov., is proposed with strain 1445t ^T (=DSM 21630 ^T =VKM B-2549 ^T) as the type strain.