Sulfolobus hakonensis sp. nov., a Novel Species of Acidothermophilic Archaeon

Researchers isolated and characterized a novel acidothermophilic archaeon from a hot spring in Hakone, Japan. The isolate, designated strain H01-1, is a facultative chemolithoautotroph with lobed-shaped cells approximately 1.0 μm in diameter that grows optimally at pH 3.0 and 70°C (range: pH 1.0–4.0, 50–80°C). The organism is strictly aerobic and can obtain energy by oxidizing elemental sulfur and reduced sulfur compounds, though it grows poorly on sugars and amino acids as sole carbon sources. Analysis revealed a genomic DNA G+C content of 38.4 mol% and lipid composition characteristic of the Sulfolobaceae family, particularly the presence of calditoglycerocaldarchaeol. Phylogenetic analysis using 16S rRNA sequences showed less than 89.8% similarity to known Sulfolobus species, and DNA-DNA hybridization values were very low (approximately 3–6%) compared to related species. Based on these phenotypic, genetic, and molecular characteristics, the authors propose this organism as a new species, Sulfolobus hakonensis, which can be distinguished from previously described Sulfolobus species by its limited ability to utilize sugars and amino acids.

Key findings

• Strain H01-1 is a newly identified acidothermophilic archaeon isolated from a Japanese hot spring with optimal growth at pH 3.0 and 70°C, representing a facultative chemolithoautotroph dependent on sulfur oxidation for energy.
• The organism exhibits a genomic DNA G+C content of 38.4 mol% and characteristic lipid composition placing it in genus Sulfolobus but distinguishes itself from known species by poor utilization of sugars and amino acids.
• 16S rRNA sequence analysis revealed less than 89.8% similarity to existing Sulfolobus species, and DNA-DNA hybridization showed only 3–6% relatedness to S. acidocaldarius and S. solfataricus.
• The proposed species Sulfolobus hakonensis is strictly aerobic, cannot grow under anaerobic conditions, and exhibits morphological features including a regularly arranged cell wall structure typical of Sulfolobaceae family members.
• Phylogenetic reconstruction based on 16S rRNA sequences confirmed S. hakonensis as a genetically distinct member of the Sulfolobus genus, warranting formal species designation.