Natranaerobius thermophilus gen. nov., sp. nov., a halophilic, alkalithermophilic bacterium from soda lakes of the Wadi An Natrun, Egypt, and proposal of Natranaerobiaceae fam. nov. and Natranaerobiales ord. nov.

Abstract

Novel halophilic, alkalithermophilic, Gram-type-positive bacterial strains were isolated from sediment of alkaline, hypersaline lakes of the Wadi An Natrun, Egypt. Cells of strain JW/NM-WN-LF^Twere rod-shaped, non-spore-forming and non-motile. Strain JW/NM-WN-LF^Tgrew (at pH^55 °C 9.5) between 35 and 56 °C, with an optimum at 53 °C. The pH^55 °Crange for growth was 8.3–10.6, with an optimum at pH^55 °C 9.5 and no growth at pH^55 °C 8.2 or below, or at pH^55 °C 10.8 or above. At the optimum pH and temperature, the strain grew in the Na⁺range of 3.1–4.9 M (1.5–3.3 M added NaCl) and optimally between 3.3 and 3.9 M Na⁺(1.7–2.3 M added NaCl). Strain JW/NM-WN-LF^Tutilized fructose, cellobiose, ribose, trehalose, trimethylamine, pyruvate, Casamino acids, acetate, xylose and peptone as carbon and energy sources. Fumarate (20 mM), S₂O₃²⁻(20 mM), NO₃⁻(20 mM) and iron(III) citrate (20 mM) were utilized as electron acceptors. During growth on sucrose, the isolate produced acetate and formate as major fermentation products. Main cellular fatty acids were iso-branched 15 : 0, i17 : 0 dimethylacetal and 16 : 0 dimethylacetal. The G+C content of genomic DNA was 40.4 mol% (HPLC). On the basis of genotypic and phenotypic characteristics, it is proposed that strain JW/NM-WN-LF^Trepresents a novel genus and species,Natranaerobius thermophilusgen. nov., sp. nov. The type strain is JW/NM-WN-LF^T(=DSM 18059^T=ATCC BAA-1301^T). Based on 16S rRNA gene sequence analysis, the strain forms a novel lineage within the class ‘Clostridia’ and clusters with uncultivated bacteria and unidentified strains retrieved from alkaline, hypersaline environments. The phylogenetic data suggest that the lineage represents a novel family,Natranaerobiaceaefam. nov., and order,Natranaerobialesord. nov.