Phreatobacter aquiterrae sp. nov., isolated from an Icelandic subsurface geothermal aquifer

A novel bacterial strain, designated HK31-P^T, was isolated from a deep subsurface geothermal aquifer in southwestern Iceland. Phylogenetic analyses, based on 16S rRNA gene sequences, revealed that the strain was affiliated to the genus Phreatobacter. Cells of the strain were Gram-negative, rod-shaped, motile by means of a polar flagellum and granule-containing. Colonies were small, circular, convex, smooth and white in colour. Growth under chemoorganoheterotrophic and aerobic conditions was observed at the following ranges: 20-35 °C (optimum, 30-35 °C), pH 7-9 (optimum, 8) and 0-0.5% salinity (optimum, 0%). The strain was also capable of growing under chemolithoautotrophic and (micro)aerobic conditions with Fe(II) as an electron donor. The major respiratory quinone identified was ubiquinone Q-10 (97.0%), and the predominant fatty acid was C_18:1  ω7c. The dominant polar lipids consisted of diphosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, phosphatidylglycerol and an unidentified aminophospholipid, along with several unidentified glycolipids, phospholipids and lipids. The G+C content of the genomic DNA of strain HK31-P^T was 67.66 mol%, and its complete genome was 4.34 Mbp in size. The values of the digital DNA-DNA hybridization and average nucleotide identity indices between strain HK31-P^T and the type species of the genus Phreatobacter ranged, respectively, from 21.30 to 27% and from 78.25 to 86.32%. These values are well below the accepted species delineation thresholds, thereby clearly indicating that strain HK31-P^T represents a distinct genomic species within the genus Phreatobacter, strongly supporting that the former represents a new species belonging to the genus Phreatobacter. Therefore, based on this polyphasic approach, strain HK31-P^T represents a new species within the genus Phreatobacter, for which the name Phreatobacter aquiterrae sp. nov. is proposed. The type strain is HK31-P^T (DSM 116433^T=UBOCC-M-3430^T).