L'Haridon, Stéphane

A novel hyperthermophilic, heterotrophic and anaerobic archaeon, designated strain SLHALR2 T , was isolated from the ‘Cooking Pots’ hot springs at Hell’s Gate, Tikitere, New Zealand. During the exponential growth phase, cells of strain SLHALR2 T appear as long, thin rods to filaments, measuring 0.25–0.4 µm in width and 3.0–7.0 µm in length. Strain SLHALR2 T 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 SLHALR2 T 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 SLHALR2 T 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 SLHALR2 T as a distinct species within Infirmifilum . Based on phylogenomic analyses and the physiological characteristics of the novel isolate, strain SLHALR2 T 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.