Infirmifilum tikiterense sp. nov., a novel free-living hyperthermophilic anaerobic heterotrophic archaeon isolated from a New Zealand hot spring, emendation of the genus Infirmifilum.

A novel hyperthermophilic, heterotrophic and anaerobic archaeon, designated strain SLHALR2T, was isolated from the 'Cooking Pots' hot springs at Hell's Gate, Tikitere, New Zealand. During the exponential growth phase, cells of strain SLHALR2T appear as long, thin rods to filaments, measuring 0.25-0.4 µm in width and 3.0-7.0 µm in length. Strain SLHALR2T grows at temperatures ranging from 60 to 97 °C (optimum 80-85 °C), at pH values between 5.0 and 7.3 (optimum pH 6.0) and with 0-8 g l-1 sodium chloride concentration (optimum 0-1.0 g l-1). Elemental sulphur is reduced to hydrogen sulphide. Strain SLHALR2T is an obligate organotroph capable of utilizing a variety of proteinaceous substrates and a limited range of sugars. Archaeal cell extracts improve growth but are not mandatory for growth. Phylogenetic analysis based on 16S rRNA gene sequence comparisons indicates that strain SLHALR2T belongs to the genus Infirmifilum within the family Thermofilaceae, order Thermofilales (phylum Thermoproteota). The strain shares 98.4-99% 16S rRNA gene sequence similarity with described Infirmifilum species. Despite this high level of 16S rRNA gene similarity with recently described Infirmifilum species, both average nucleotide identity (71-74%), average amino acid identity (67-75.5%) values and digital DNA-DNA hybridization values support the designation of strain SLHALR2T as a distinct species within Infirmifilum. Based on phylogenomic analyses and the physiological characteristics of the novel isolate, strain SLHALR2T is proposed as the type strain of a new species, Infirmifilum tikiterense sp. nov. (=OCM2026=UBOCC M-3571), and an emended description of the genus Infirmifilum is proposed.