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Volume 1 (2002), Issue 2, Pages 113-121
Research Article

Pyrobaculum calidifontis sp. nov., a novel hyperthermophilic archaeon that grows in atmospheric air

1Department of Synthetic Chemistry and Biological Chemistry, Graduate School of Engineering, Kyoto University, Yoshida-Honmachi, Sakyo-ku, Kyoto 606-8501, Japan, and Core Research for Evolutional Science and Technology Program of Japan Science and Technology Corporation (CREST-JST), Kawaguchi, Saitama 332-0012, Japan
2National Institute of Molecular Biology and Biotechnology, University of the Philippines Los Baños, College 4031, Laguna, Philippines

Received 10 May 2001; Accepted 1 March 2002

Copyright © 2002 Hindawi Publishing Corporation. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


A novel, facultatively aerobic, heterotrophic hyperthermophilic archaeon was isolated from a terrestrial hot spring in the Philippines. Cells of the new isolate, strain VA1, were rod-shaped with a length of 1.5 to 10 μm and a width of 0.5 to 1.0 μm. Isolate VA1 grew optimally at 90 to 95 °C and pH 7.0 under atmospheric air. Oxygen served as a final electron acceptor under aerobic growth conditions, and vigorous shaking of the medium significantly enhanced growth. Elemental sulfur inhibited cell growth under aerobic growth conditions, whereas thiosulfate stimulated cell growth. Under anaerobic growth conditions, nitrate served as a final electron acceptor, but nitrite or sulfur-containing compounds such as elemental sulfur, thiosulfate, sulfate and sulfite could not act as final electron acceptors. The G+C content of the genomic DNA was 51 mol%. Phylogenetic analysis based on 16S rRNA sequences indicated that strain VA1 exhibited close relationships to species of the genus Pyrobaculum. A DNA–DNA hybridization study revealed a low level of similarity (≤ 18%) between strain VA1 and previously described members of the genus Pyrobaculum. Physiological characteristics also indicated that strain VA1 was distinct from these Pyrobaculum species. Our results indicate that isolate VA1 represents a novel species, named Pyrobaculum calidifontis.