Downloaded from www.microbiologyresearch.org by IP: 54.70.40.11 On: Wed, 05 Dec 2018 06:14:28 International Journal of Systematic and Evolutionary Microbiology (2000), 50, 1601–1609 Printed in Great Britain Thermacetogenium phaeum gen. nov., sp. nov., a strictly anaerobic, thermophilic, syntrophic acetate-oxidizing bacterium Satoshi Hattori, 1,2 Yoichi Kamagata, 1 Satoshi Hanada 1 and Hirofumi Shoun 2 Author for correspondence : Yoichi Kamagata. Tel : ›81 298 61 6591. Fax: ›81 298 61 6587. e-mail : kamagata!nibh.go.jp 1 National Institute of Bioscience and Human Technology, Agency of Industrial Science and Technology, 1-1 Higashi, Tsukuba, Ibaraki 305-8566, Japan 2 Institute of Applied Biochemistry, University of Tsukuba, 1-1-1 Tennodai, Tsukuba, Ibaraki 305-8572, Japan A novel anaerobic, thermophilic, syntrophic acetate-oxidizing bacterium, strain PB T , was isolated from a thermophilic (55 SC) anaerobic methanogenic reactor which had been treating kraft-pulp waste water. The bacterium oxidized acetate in co-culture with a thermophilic hydrogenotrophic methanogen. Strain PB T , a Gram-positive, spore-forming, rod-shaped bacterium grew optimally at 58 SC and pH 6<8. The bacterium grew acetogenically on several alcohols, methoxylated aromatics, pyruvate, glycine, cysteine, formate and hydrogen/CO 2 . Strain PB T also oxidized acetate with reduction of sulfate or thiosulfate as the electron acceptor. The bacterium contained MK-7 as the major quinone. The GMC content of the DNA was 53<5 mol %. Comparative 16S rDNA analysis indicated that strain PB T belongs to the Bacillus–Clostridium subphylum. However, it was distant from any known genera or micro- organism. The closest known relative was Thermoterrabacterium ferrireducens with 87<4 % similarity. The name Thermacetogenium phaeum gen. nov., sp. nov. is proposed. The type strain is strain PB T (fl DSM 12270 T ). Keywords : Thermacetogenium phaeum gen. nov., sp. nov., thermophile, syntrophic acetate oxidation, acetogen, sulfate reduction INTRODUCTION Acetate is one of the most important intermediates for methanogenesis in anaerobic mineralization of organic materials. It has been estimated that approximately 70–80 % of methane is derived from acetate in anoxic environments (Mountfort & Asher, 1978 ; Mackie & Bryant, 1981 ; Lovley & Klug, 1982). Of the number of methanogens described, only the genera Methano- sarcina and Methanosaeta are known to produce methane from acetate. Methanogenesis from acetate in these organisms is catalysed by an aceticlastic reaction in which the methyl group of acetate is reduced to methane (Ferry, 1992). In contrast to these organisms, some syntrophic proton-reducing organisms were found to oxidize acetate to form methane in associ- ation with hydrogenotrophic methanogens (Zinder & Koch, 1984 ; Lee & Zinder, 1988 ; Schnu$ rer et al., 1994, 1996). Metabolically, this syntrophic association con- sists of two reactions that were originally proposed by ................................................................................................................................................. The GenBank/EMBL/DDBJ accession number for the 16S rDNA sequence of strain PB T is AB020336. Barker (1936). In the first reaction, acetate is oxidized to form hydrogen and CO # , which are, in the second reaction, converted to methane. As with other an- aerobic syntrophic fatty acid oxidations, the former reaction is thermodynamically unfavourable under standard conditions, unless it couples with the latter reaction (Stams, 1994 ; Schink, 1997). Thus, syntrophic acetate degradation is possible only when syntrophic and hydrogen-consuming micro-organisms cooperate. To date, two syntrophic acetate oxidizers in associ- ation with hydrogenotrophic methanogens are known. The first description was strain AOR, which was a thermophilic acetate oxidizer isolated from a methano- genic reactor in co-culture with Methanobacterium sp. (Zinder & Koch, 1984). The isolate was later found to be a homoacetogen which forms acetate from hy- drogen and CO # in pure culture, whereas acetate oxidation, i.e. the reverse of acetogenesis, occurs in co- culture with the methanogen (Lee & Zinder, 1988). The second acetate syntroph described was Clostridium ultunense, which mesophilically oxidizes acetate in the presence of hydrogenotrophic methanogens (Schnu$ rer et al., 1994, 1996). Although C. ultunense is phylo- 01214 # 2000 IUMS 1601