Downloaded from www.microbiologyresearch.org by IP: 54.70.40.11 On: Mon, 19 Nov 2018 13:33:17 International Journal of Systematic and Evolutionary Microbiology (2000), 50, 771–779 Printed in Great Britain Syntrophothermus lipocalidus gen. nov., sp. nov., a novel thermophilic, syntrophic, fatty-acid-oxidizing anaerobe which utilizes isobutyrate Yuji Sekiguchi, 1 Yoichi Kamagata, 2 Kazunori Nakamura, 2 Akiyoshi Ohashi 1 and Hideki Harada 1 Author for correspondence : Yuji Sekiguchi. Tel : 81 258 47 9623. Fax: 81 258 47 9623. e-mail : skgcvos.nagaokaut.ac.jp 1 Department of Environmental Systems Engineering, Nagaoka University of Technology, Nagaoka, Kamitomioka 1603-1, Niigata 940-2188, Japan 2 National Institute of Bioscience and Human Technology, Agency of Industrial Science and Technology, Tsukuba, Ibaraki 305-8566, Japan A new anaerobic, thermophilic, syntrophic, fatty-acid-oxidizing bacterium designated strain TGB-C1 T was isolated from granular sludge in a thermophilic upflow anaerobic sludge blanket (UASB) reactor. The cells were slightly curved rods and were weakly motile. Spore formation was not observed. The optimal temperature for growth was around 55 SC and growth occurred in the range 45 to 60 SC. The pH range for growth was 58–75, and the optimum pH was 65–70. Crotonate was the only substrate that allowed the strain to grow in pure culture. However, in co-culture with the thermophilic, hydrogenotrophic Methanobacterium thermoautotrophicum strain ΔH, the isolate could syntrophically oxidize saturated fatty acids with 4–10 carbon atoms, including isobutyrate. During the degradation of isobutyrate by the co-culture, isobutyrate was isomerized to butyrate, which was then oxidized. The strain was not able to utilize sulfate, sulfite, thiosulfate, nitrate, fumarate or Fe(III) as electron acceptor. The DNA base composition was 510 mol%. 16S rDNA sequence analysis revealed that the strain belongs to the family Syntrophomonadaceae, but it was only distantly related to other known species of β-oxidizing syntrophs. Hence, the name Syntrophothermus lipocalidus is proposed for TGB-C1 T as a new species of a new genus. Keywords : anaerobe, fatty acid oxidation, syntroph, thermophilic, Syntrophothermus lipocalidus INTRODUCTION Conversion of complex organic matter to methane and carbon dioxide in anaerobic ecosystems is performed by cooperations of different trophic groups of microbes. In this type of ecosystem, fatty acids such as propionate and butyrate are frequently formed as intermediates. The oxidation of these compounds is thermodynamically unfavourable under such environ- ments unless the consumption of the reducing equivalents, i.e. hydrogen andor formate, is coupled with the oxidation reaction (Schink, 1992, 1997). Consequently, fatty acid oxidation requires syntrophic ................................................................................................................................................. Abbreviation : UASB, upflow anaerobic sludge blanket. The GenBank/EMBL/DDBJ accession number for the 16S rDNA sequence of strain TGB-C1 T is AB021305. interactions between two different microbes, a fatty acid β-oxidizing, hydrogen-producing bacterium and a hydrogenotrophic microbe such as a methanogen. To date, several mesophilic anaerobes which perform syntrophic fatty acid β-oxidation have been isolated in co-culture with hydrogen-utilizing microbes. Syntro- phomonas wolfei (subsp. wolfei) was the first strain isolated in co-culture with a hydrogenotrophic meth- anogen or sulfate-reducer (McInerney et al., 1981, 1979). In addition, Syntrophospora bryantii (Stieb & Schink, 1985 ; Zhao et al., 1990), Syntrophomonas sapovorans (Roy et al., 1986), Syntrophomonas wolfei subsp. saponavida (Lorowitz et al., 1989), ‘ Syntrophus aciditrophicus ’ (Jackson et al., 1999) and several unnamed mesophilic β-oxidizing syntrophs have been isolated and characterized (Shelton & Tiedje, 1984 ; Wu et al., 1992; Zhao et al., 1993). Since Beaty & McInerney (1987) reported that Syntrophomonas 01212  2000 IUMS 771