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).

Characterization of Desulfovibrio salinus sp. nov., a slightly halophilic sulfate-reducing bacterium isolated from a saline lake in Tunisia.

A novel slightly halophilic sulfate-reducing bacterium, designated strain P1BSRT, was isolated from water of a saline lake in Tunisia. Strain P1BSRT had motile (single polar flagellum), Gram-negative, rod-shaped, non-spore-forming cells, occurring singly or in pairs. Strain P1BSRT grew at temperatures between 15 and 45 °C (optimum 40 °C), and in a pH range between 6 and 8.5 (optimum pH 6.7). The strain required NaCl for growth (1 % w/v), and tolerated high NaCl concentration (up to 12 % w/v) with an optimum of 3 % (w/v). Sulfate, thiosulfate and sulfite served as terminal electron acceptors, but not elemental sulfur, fumarate, nitrate and nitrite. Strain P1BSRT utilized lactate, pyruvate, formate, d-fructose and glycerol as carbon and energy sources. The main cellular fatty acid was C16 : 0 (50.8 %). The genomic DNA G+C content was 47.7 mol%. Phylogenetic analysis of 16S rRNA gene sequence similarity indicated that strain P1BSRT was affiliated to the genus Desulfovibrio, with the type strains Desulfovibrio salexigens (96.51 %), Desulfovibrio zosterae (95.68 %), Desulfovibrio hydrothermalis (94.81 %) and Desulfovibrio ferrireducens (94.73 %) as its closest phylogenetic relatives. On the basis of genotypic, phenotypic and phylogenetic characteristics, it is proposed to assign strain P1BSRT to a novel species of the genus Desulfovibrio, Desulfovibrio salinus sp. nov. The type strain is P1BSRT (=DSM 101510T=JCM 31065T).

Desulfovibrio senegalensis sp. nov., a mesophilic sulfate reducer isolated from marine sediment.

Several strains of sulfate-reducing bacteria were isolated from marine sediments recovered from Hann Bay (Senegal). All were related to members of the genus Desulfovibrio. A strictly anaerobic, mesophilic and moderately halophilic strain designated BLaC1T was further characterized. Cells of strain BLaC1T stained Gram-negative and were 0.5 µm wide and 2-4 µm long, motile, rod-shaped and non-spore-forming. The four major fatty acids were anteiso-C15 : 0, iso-C15 : 0, iso-C17 : 0 and anteiso-C17 : 0. Growth was observed from 15 to 45 °C (optimum 40 °C) and at pH 5.5-8 (optimum pH 7.5). The salinity range for growth was 5-65 g NaCl l-1 (optimum 30 g l-1). Yeast extract was required for growth. Strain BLaC1T was able to grow on lactate and acetate in the presence of sulfate as an electron acceptor. Sulfate, thiosulfate and sulfite could serve as terminal electron acceptors, but not fumarate, nitrate or elemental sulfur. The DNA G+C content was 55.8 mol%. 16S rRNA gene sequence analysis assigned strain BLaC1T to the family Desulfovibrionaceae; its closest relative was Desulfovibrio oxyclinae DSM 19275T (93.7 % similarity). On the basis of 16S rRNA gene sequence comparisons and physiological characteristics, strain BLaC1T is proposed as representing a novel species of Desulfovibrio, with the name Desulfovibrio senegalensis sp. nov. The type strain is BLaC1T (=DSM 101509T=JCM 31063T).

Mobilisporobacter senegalensis gen. nov., sp. nov., an anaerobic bacterium isolated from tropical shea cake.

A Gram-stain positive, endospore-forming, strictly anaerobic bacterium, designated strain Gal1T, was isolated from shea cake, a waste material from the production of shea butter, originating from Saraya, Senegal. The cells were rod-shaped, slightly curved, and motile with peritrichous flagella. The strain was oxidase-negative and catalase-negative. Growth was observed at temperatures ranging from 15 to 45 °C (optimum 30 °C) and at pH 6.5-9.3 (optimum pH 7.8). The salinity range for growth was 0-3.5 % NaCl (optimum 1 %). Yeast extract was required for growth. Strain Gal1T fermented various carbohydrates such as mannose, mannitol, arabinose, cellobiose, fructose, glucose, maltose, sucrose, trehalose and lactose and the major end-products were ethanol and acetate. The only major cellular fatty acid was C16 : 0 (19.6 %). The DNA base G+C content of strain Gal1T was 33.8 mol%. Analysis of the 16S rRNA gene sequence of the isolate indicated that this strain was related to Mobilitalea sibirica DSM 26468T with 94.27 % similarity, Clostridium populeti ATTC 35295T with 93.94 % similarity, and Clostridium aminovalericum DSM 1283T and Anaerosporobacter mobilis DSM 15930T with 93.63 % similarity. On the basis of phenotypic characteristics, phylogenetic analysis and the results of biochemical and physiological tests, strain Gal1T was clearly distinguished from closely related genera, and strain Gal1T can be assigned to a novel species of a new genus for which the name Mobilisporobacter senegalensis gen. nov., sp. nov. is proposed. The type strain is Gal1T ( = DSM 26537T = JCM 18753T).