Guyparkeria halopsychrophila sp. nov., a chemolithoautotrophic polyextremophile isolated from a sub-zero Arctic hypersaline spring.

Two eurypsychrophilic and halophilic sulphur-oxidizing bacterial strains (LHSS19-1^T and GHLCS8-2) were isolated from High Arctic hypersaline sulphur spring sediment samples collected from the Lost Hammer and Gypsum Hill spring systems on Axel Heiberg Island in the Qikiqtaaluk Region, Nunavut, Canada. The strains were obligate chemolithoautotrophs, utilizing reduced sulphur compounds (thiosulphate, sulphide, tetrathionate and elemental sulphur) as electron donors and energy sources. Chemolithoautotrophic growth on thiosulphate was observed at -2 to 37 °C, pH 6.5-9.5 and NaCl concentrations of 1-20 % w/v. The DNA G+C content of the draft genome sequences was 64.59-64.74 mol%. Phylogenetic analyses based on 16S rRNA gene sequences, 92 single-copy core genes and whole genomes indicated that both strains together form a distinct monophyletic clade within the genus Guyparkeria. Moreover, in silico DNA-DNA hybridization, orthologous average nt identity and average aa identity values calculated between each strain and the closest related type strains were ≤69.10%, 87.83% and 90.37%, respectively. The genomes of both strains encoded high O₂ affinity cbb3-type cytochrome c oxidase genes but distinctively lacked a complete set of aa3-type cytochrome c oxidase genes. The dominant respiratory quinone of strain LHSS19-1^T was ubiquinone-8. The major fatty acids (>10%) were C_18 : 1  ω7c, C_12 : 0 3OH and C_16 : 0. Based on phenotypic and genotypic results, strains LHSS19-1^T and GHLCS8-2 represent a novel species within the genus Guyparkeria, for which the name Guyparkeria halopsychrophila sp. nov. is proposed. The type strain is LHSS19-1^T (=NCTC 15100^T=DSM 117890^T).