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 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.