Summary auto-generated
This study describes a new genus of archaebacteria, Acidianus, isolated from 26 strains collected from acidic geothermal environments worldwide. The defining characteristic of Acidianus species is their ability to grow facultatively as either aerobes or anaerobes through opposite metabolic modes: aerobic oxidation of elemental sulfur (producing sulfuric acid) or anaerobic reduction of sulfur with hydrogen (producing hydrogen sulfide). All isolates share a DNA guanine-plus-cytosine content of 31 mol%, distinct from most Sulfolobus species at 37 mol%. The genus includes the new type species Acidianus infernus and Acidianus brierleyi, which was reclassified from Sulfolobus after discovering its anaerobic sulfur-reducing capability—a trait previously unrecognized. Unlike strictly aerobic Sulfolobus species, Acidianus members are obligately chemolithotrophic, strictly dependent on sulfur metabolism. The organisms are extreme thermoacidophiles thriving between pH 1-6 and 45-96°C, with optimal growth around 90°C and pH 2. Genetically and biochemically, they represent a distinct group within the archaebacteria, capable of exploiting both oxidizing surface environments and reducing subsurface zones of geothermal habitats.
Key findings
- A new archaebacterial genus Acidianus is established, comprising facultatively aerobic sulfur-metabolizing thermoacidophiles with 31 mol% DNA G+C content, distinct from aerobic Sulfolobus species
- Acidianus species uniquely employ two opposite metabolic pathways depending on oxygen availability: aerobic sulfur oxidation or anaerobic sulfur reduction coupled to hydrogen oxidation
- Sulfolobus brierleyi is reclassified as Acidianus brierleyi based on demonstrated anaerobic sulfur-reduction capability and genetic evidence, fundamentally altering understanding of this organism's metabolism
- All 26 isolates are obligate chemolithoautotrophs strictly dependent on elemental sulfur, unable to grow heterotrophically on organic compounds alone, contrasting with some Sulfolobus species
- Acidianus species were isolated from geothermal environments across Italy, Iceland, the Azores, and the United States, suggesting worldwide distribution in acidic hot springs and hydrothermal systems
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Abstract
A new genus, Acidianus, is characterized from studies of 26 isolates of thermoacidophilic archaebacteria from different solfatara fields and marine hydrothermal systems; these isolates grow as facultative aerobes by lithotrophic oxidation and reduction of SO, respectively, and are therefore different from the strictly aerobic Sulfolobus species. The Acidianus isolates have a deoxyribonucleic acid guanine-plus-cytosine content of 31 mol%. In contrast, two of three Sulfolobus species, including the type species, have a guanine-plus-cytosine content of 37 mol%; Sulfolobus brierleyi is the exception, with a guanine-plus-cytosine content of 31 mol%. In contrast to its earlier descriptions, S. brierleyi is able to grow strictly anaerobically by hydrogen-sulfur autotrophy. Therefore, it is described here as a member of the genus Acidianus. The following species are assigned to the genus Acidianus: Acidianus infernus sp. nov. (type strain, strain DSM 3191) and Acidianus brierleyi comb. nov. (type strain, strain DSM 1651).