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Isolation and characterization of a thermophilic sulfur- and iron-reducing thaumarchaeote from a terrestrial acidic hot spring


A deep-branching clade of Thaumarchaeota, conventionally called Terrestrial hot spring creanarchaeotic group (THSCG), is a missing link between thaumarchaeotic ammonia oxidizers and the deeper-branching non-ammonia oxidizers, such as Crenarchaeota and Candidatus Korarchaeota. Here, we report isolation of the first cultivated representative from the THSCG, named as NAS-02. Physiological characterization demonstrated that the isolate was a thermoacidophilic, sulfur- and iron-reducing organoheterotroph, which was supported by gene contents encoded in its complete genome. There was no evidence for ammonia oxidation by the isolate. Members in THSCG are likely thermophiles, and may play roles in degrading cell debris as a scavenger and in biogeochemical cycling of sulfur and iron in the hot environments, as suggested by the physiological characteristics of the isolate and the geographical distribution of the 16S rRNA gene sequences of THSCG in terrestrial hot springs and marine hydrothermal fields. Phylogenetic analysis suggests that the THSCG lineage represented by NAS-02 has gained the ability of sulfur reduction via horizontal gene transfer. Based on the phylogeny and physiology, we propose the name Conexivisphaera calidus gen. nov., sp. nov. to accommodate the isolate.

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We would like to thank the owner of the spa for permitting us to collect hot spring samples. We also would thank Dr. Kenshiro Oshima and Dr. Masahira Hattori (The University of Tokyo) for their help on genome sequencing. We would also like to thank anonymous reviewers for their helpful and insightful suggestions. This work was supported by RIKEN Special Postdoctoral Researchers Program, RIKEN Incentive Research Grant and Institute of Fermentation (IFO), Osaka, and partially by the Cabinet Office, Government of Japan, through the Next-generation Technology for Ocean Resources Exploration (called as Zipangu-in-the-ocean project) in the Cross-ministerial Strategic Innovation Promotion Program (SIP).

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S.K., T.I., and Mo.O. conceived this study. S.K., T.I., T.T., K.S., and Mo.O. supervised experiments and analyses. S.K., T.I., M.N., Ma.O., M.Y., and K.U. performed analyses. S.K., T.I., and Mo.O. wrote the paper with contributions from all authors.

Correspondence to Shingo Kato.

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