ORIGINAL PAPER T. Sokolova Æ J. Hanel Æ R. U. Onyenwoke A.-L. Reysenbach Æ A. Banta Æ R. Geyer J. M. Gonza´lez Æ W. B. Whitman Æ J. Wiegel Novel chemolithotrophic, thermophilic, anaerobic bacteria Thermolithobacter ferrireducens gen. nov., sp. nov. and Thermolithobacter carboxydivorans sp. nov. Received: 2 May 2006 / Accepted: 17 July 2006 / Published online: 5 October 2006 Ó Springer-Verlag 2006 Abstract Three thermophilic strains of chemolithoauto- trophic Fe(III)-reducers were isolated from mixed sedi- ment and water samples (JW/KA-1 and JW/KA-2 T : Calcite Spring, Yellowstone N.P., WY, USA; JW/JH- Fiji-2: Savusavu, Vanu Levu, Fiji). All were Gram stain positive rods (0.5 · 1.8 lm). Cells occurred singly or in V-shaped pairs, and they formed long chains in complex media. All utilized H 2 to reduce amorphous iron (III) oxide/hydroxide to magnetite at temperatures from 50 to 75°C (opt. 73°C). Growth occurred within the pH 60C range of 6.5–8.5 (opt. pH 60C 7.1–7.3). Magnetite pro- duction by resting cells occurred at pH 60C 5.5–10.3 (opt. 7.3). The iron (III) reduction rate was 1.3 lmol Fe(II) produced · h -1 · ml 1 in a culture with 3 · 10 7 cells, one of the highest rates reported. In the presence or absence of H 2 , JW/KA-2 T did not utilize CO. The G + C con- tent of the genomic DNA of the type strain is 52.7 ± 0.3 mol%. Strains JW/KA-1 and JW/KA-2 T each contain two different 16S rRNA gene sequences. The 16S rRNA gene sequences from JW/KA-1, JW/KA- 2 T , or JW/JH-Fiji-2 possessed >99% similarity to each other but also 99% similarity to the 16S rRNA gene sequence from the anaerobic, thermophilic, hydrogeno- genic CO-oxidizing bacterium ‘Carboxydothermus re- strictus’ R1. DNA–DNA hybridization between strain JW/KA-2 T and strain R1 T yielded 35% similarity. Physiological characteristics and the 16S rRNA gene sequence analysis indicated that the strains represent two novel species and are placed into the novel genus Ther- molithobacter within the phylum ‘Firmicutes’. In addi- tion, the levels of 16S rRNA gene sequence similarity between the lineage containing the Thermolithobacter and well-established members of the three existing classes of the ‘Firmicutes’ is less than 85%. Therefore, Thermo- lithobacter is proposed to constitute the first genus within a novel class of the ‘Firmicutes’, Thermolithobacteria. The Fe(III)-reducing Thermolithobacter ferrireducens gen. nov., sp. nov. is designated as the type species with strain JW/KA-2 T (ATCC 700985 T , DSM 13639 T ) as its type strain. Strain R1 T is the type strain for the hy- drogenogenic, CO-oxidizing Thermolithobacter carb- oxydivorans sp. nov. (DSM 7242 T , VKM 2359 T ). Keywords Dissimilatory Fe(III) reduction Æ CO-metabolism Æ Thermophilic anaerobes Æ Chemolithoautotroph Æ Ferribacter thermautotrophicus Æ Carboxydothermus restrictus Æ Thermolithobacter ferrireducens Æ Thermolithobacter carboxydivorans Introduction Anaerobic, microbially-mediated processes, such as carbon monoxide oxidation and autotrophic iron (III) reduction, may have been important on primitive Earth, which contained a reduced atmosphere and very low levels of oxygen (Lovley 1991; Gold 1992). Increasingly Communicated by F. Robb. T. Sokolova Winogradsky Institute of Microbiology, Russian Academy of Sciences, Prospect 60-letiya Oktyabrya 7/2, 117312 Moscow, Russia J. Hanel Æ R. U. Onyenwoke Æ W. B. Whitman Æ J. Wiegel (&) Department of Microbiology, The University of Georgia, 527 Biological Sciences Bldg, 1000 Cedar Street, Athens, GA 30602, USA E-mail: jwiegel@uga.edu Fax: +1-706-5422651 A.-L. Reysenbach Æ A. Banta Department of Biology, Portland State University, PO Box 751, Portland, OR 97207-0751, USA R. Geyer Environmental Microbiology, UFZ Centre for Environmental Research Leipzig-Halle, 04318 Leipzig, Germany J. M. Gonza´lez Instituto de Recursos Naturales y Agrobiologia, CSIC, Apartado 1052, 41080 Sevilla, Spain Extremophiles (2007) 11:145–157 DOI 10.1007/s00792-006-0022-5