Stygiolobus caldivivus sp. nov., a facultatively anaerobic hyperthermophilic archaeon isolated from the Unzen hot spring in Japan

Abstract

A novel hyperthermophilic, acidophilic and facultatively anaerobic archaeon, strain KN-1 T , was isolated from Unzen hot spring in Japan and characterized. The cells of KN-1 T were irregular cocci with a diameter of 1.0–3.0 µm that grew at 55–87.5 °C (optimum: 75 °C) and pH 1.0–5.5 (optimum: 3.0). Chemolithoautotrophic growth of KN-1 T occurred in the presence of S 0 or H 2 under oxic conditions. Under anoxic conditions, KN-1 T grew with S 0 , ferric citrate and FeCl 3 as electron acceptors. A phylogenetic analysis of 16S rRNA gene sequences showed that the species most closely related to KN-1 T was Stygiolobus azoricus JCM 9 021 T , with 98.9 % sequence identity, indicating that strain KN-1 T belongs to the genus Stygiolobus . This genus has been considered to consist of obligate anaerobes since its description in 1991. However, KN-1 T grew under oxic, microoxic and anoxic conditions. Moreover, KN-1 T utilized various complex substrates and some sugars as carbon or energy sources, which is also different from S. azoricus JCM 9 021 T . The average nucleotide identity and amino acid identity values between KN-1 T and S. azoricus JCM 9 021 T were 79.4 and 76.1 %, respectively, indicating that KN-1 T represents a novel species. Its main polar lipids were calditoglycerocaldarchaeol and caldarchaeol, and its DNA G+C content was 40.1 mol%. We also found that S. azoricus JCM 9021 T grew under microoxic conditions in the presence of H 2 as an electron donor, indicating that this genus does not comprise obligate anaerobes. Based on this polyphasic taxonomic analysis, we propose the novel species, Stygiolobus caldivivus sp. nov., whose type strain is KN-1 T (=JCM 34 622 T =KCTC 4 293 T ).

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