Thermospira aquatica gen. nov., sp. nov., a novel thermophilic spirochete isolated from a Tunisian hot spring, and description of the novel family Thermospiraceae.

A novel thermophilic, anaerobic bacterium, strain F1F22T, was isolated from hot spring water collected in northern Tunisia. The cells were non-motile, Gram-negative and helical with hooked ends, 0.5×10-32 µm in size. Growth of the strain was observed at 45-70 °C (optimum, 55 °C), in 0.0-1.0 % (w/v) NaCl (optimum without NaCl) and at pH 6.5-8.5 (optimum, pH 7.5). Yeast extract was required for growth, and the strain grew on glucose, sucrose and maltose. The major fatty acids were C16:0 (40.2 %), iso-C16: 0 (30.2 %) and C16 :0 DMA (14.5 %). The genome consisted of a circular chromosome (2.5 Mb) containing 2672 predicted protein-encoding genes with a G+C content of 43.15 mol %. Based on a comparative 16S rRNA gene sequence analysis, strain F1F22T formed a deeply branching lineage within the phylum Spirochaetota, class Spirochaetia, order Brevinematales, and had only low sequence similarity to other species of the phylum (lower than 83 %). Genome-based analysis of average nucleotide identity and digital DNA-DNA hybridization of strain F1F22T with Treponema caldarium DSM 7334T, Brevinema andersonii ATCC 43811T and Spirochaeta thermophila DSM 6578T showed values between 63.26 and 63.52 %, and between 20 and 25 %. Hence, we propose strain F1F22T as a representative of a novel family (Thermospiraceae fam. nov.), genus and species of Brevinematales: Thermospira aquatica gen. nov., sp. nov. (type strain F1F22T=JCM 31314T=DSM 101182T).

Thermanaeromonas burensis sp. nov., a thermophilic anaerobe isolated from a subterranean clay environment.

A strictly anaerobic, thermophilic and halotolerant strain, designated IA106T, was isolated from the seepage water collected in a metal biocorrosion test at a depth of 490 m, in a 130-160 m thick, subterranean Callovo-Oxfordian clay formation (158-152 million years old) in northern France. This geological formation has been selected as the potential host rock for the French high-level nuclear waste repository. Cells of strain IA106T stained Gram-positive and were non-motile, spore-forming, straight rods (0.5 × 2-6 µm). The five major fatty acids were C16 : 0 (15.9 %), C18 : 0 (15.4 %), iso-C17 : 1 I and/or anteiso-C17 : 1 B(14.8 %), iso-C17 : 0 (14.7 %) and iso-C15 : 0 (13.0 %). Growth was observed at temperatures ranging from 55 to 70 °C and at pH 5.5-9. The salinity range for growth was 0-20 g NaCl 1- 1. Yeast extract was required for growth. Strain IA106T was able to grow on lactate and various sugars in the presence of thiosulfate as electron acceptor. Sulfate, sulfite, elemental sulfur, fumarate, nitrate and nitrite were not reduced. The DNA G+C content was 60.2 mol%. 16S rRNA gene sequence analysis indicated that strain IA106T belonged to the family Thermoanaerobacteraceae, class Clostridia, phylum Firmicutes, and was most closely related to Thermanaeromonas toyohensis DSM 14490T (95.16 % 16S rRNA gene sequence similarity). On the basis of 16S rRNA gene sequence comparisons and physiological characteristics, strain IA106T represents a novel species of the genus Thermanaeromonas, for which the name Thermanaeromonas burensis sp. nov. is proposed. The type strain is IA106T ( = DSM 26576T = JCM 18718T).

Desulfosporosinus burensis sp. nov., a spore-forming, mesophilic, sulfate-reducing bacterium isolated from a deep clay environment.

A novel anaerobic, gram-positive, spore-forming, curved rod-shaped, mesophilic and sulfate-reducing bacterium was isolated from pore water collected in a borehole at -490 m in Bure (France). This strain, designated BSREI1(T), grew at temperatures between 5 °C and 30 °C (optimum 25 °C) and at a pH between 6 and 8 (optimum 7). It did not require NaCl for growth, but tolerated it up to 1.5 % NaCl. Sulfate, thiosulfate and elemental sulfur were used as terminal electron acceptors. Strain BSREI1(T) used crotonate, formate, lactate, pyruvate, fructose, glycerol and yeast extract as electron donors in the presence of sulfate. The sole quinone was MK-7. The G+C content of the genomic DNA was 43.3 mol%. Strain BSREI1(T) had the type strains of Desulfosporosinus lacus (16S rRNA gene sequence similarity of 96.83 %), Desulfosporosinus meridiei (96.31 %) and Desulfosporosinus hippei (96.16 %) as its closest phylogenetic relatives. On the basis of phylogenetic and physiological properties, strain BSREI1(T) is proposed as a representative of a novel species of the genus Desulfosporosinus, Desulfosporosinus burensis sp. nov.; the type strain is BSREI1(T) ( = DSM 24089(T) = JCM 17380(T)).