A cellulolytic anaerobic bacterium, strain 177RlBT, was isolated from a biomat sample of an Icelandic, slightly alkaline, hot spring (78 "C). Strain 177R1BT was rod-shaped, non-spore-forming, non-motile and stained Gram-negative at all stages of growth. It grew at 45-82 "C, with an optimum growth temperature around 78 "C. A t 70 "C, growth occurred at pH 58-8-0, with an optimum near pH 7.0. At the optimum temperature and pH, with 2 g cellobiose I-' as substrate, strain 177R1BT had a generation time of 2 h. During growth on Avicel, strain 177R1BT produced acetate, hydrogen and carbon dioxide as major fermentation products together with small amounts of lactic acid and ethanol. INTRODUCTIONAnaerobic micro-organisms from extreme environments and, in particular, their fermentation products and thermostable enzymes, have been the subject of much research over the past 15-20 years. Much interest has been centred on the cellulose-and hemicellulosedegrading bacteria, as these polymers constitute a large renewable resource in nature. Many of the validly described anaerobic, thermophilic, cellulose-degrading bacteria form spores and are placed in the genus Clostridium (Wiegel, 1992). In contrast, a number of anaerobic, cellulolytic, extremely thermophilic, non-spore-forming bacteria have been isolated (Huang et al., 1998;Hudson et al., 1990; t Present address: MATFORSK, Norwegian Food Research Institute, Osloveien 1, N-1430 As, Norway.The EMBL accession number for the 165 rRNA gene sequence of strain l77R1 BT is NO0481 1. Rainey et al., 1993a; Sissons et al., 1987;Svetlichnii & Svetlichnaya, 1988; Svetlichnii et al., 1990; Taya et al., 1985; Wiegel, 1992). The cellulolytic strains have been mostly isolated from neutral to alkaline hot springs. Two strains were isolated from compost (Rainey et al., 1993a) and Caldicellulosiruptor owensensis was isolated from sediment taken from Owens Lake, California, USA (Huang et al., 1998). Common features of the isolates are their high temperature habitat, ability to ferment polysaccharides, high optimum growth temperature (68-75 "C), a maximum growth temperature lower than 85 OC, a pH range for growth between pH 4.0 and 9-0, and their apparent lack of ability to form spores. By comparative 16s rDNA sequence studies, Rainey and co-workers, and later Huang and co-workers, have shown that these organisms cluster together in one group (Huang et al., 1998; Rainey et al., 1993a, b;Rainey & Stackebrandt, 1993). MladenovskaIn the present study, we have characterized a new METHODSAll diagnostic tests were performed at least twice, with triplicate determinations. Mean values are reported.Growth medium. The anaerobic medium used for cultivation was as previously described (Angelidaki et al., 1990), with the following adjustments. Avicel (2 g IF1 ; microcrystalline cellulose, FMC International) was used as carbon and energy source. The medium was supplemented with 0.10 g yeast extract 1-1 and no cysteine was added. The medium was adjusted to pH 7.0 and autoclaved at 140 "C for 20 min. Befor...

No abstract

Methanohalophilus zhilinae, a new alkaliphilic, halophilic, methylotrophic species of methanogenic bacteria, is described. Strain WeNST (T = type strain) from Bosa Lake of the Wadi el Natrun in Egypt was designated the type strain and was further characterized. This strain was nonmotile, able to catabolize dimethylsulfide, and able to grow in medium with a methyl group-containing substrate (such as methanol or trimethylamine) as the sole organic compound added. Sulfide (21 mM) inhibited cultures growing on trimethylamine. The antibiotic susceptibility pattern of strain WeNST was typical of the pattern for archaeobacteria, and the guanine-plus-cytosine content of the deoxyribonucleic acid was 38 mol% . Characterization of the 16s ribosomal ribonucleic acid sequence indicated that strain WeNST is phylogenetically distinct from members of previously described genera other than Methanohalophilus and supported the partition of halophilic methanogens into their own genus.

Characteristics of an obligately methylotrophic coccoid methanogen (strain GS-16) previously isolated from estuarine sediment are described. Growth was demonstrated on dimethyl sulfide (DMS) or trimethylamine (TMA), but not on methane thiol, methane thiol plus hydrogen, dimethyl disulfide, or methionine. DMS-grown cells were able to metabolize DMS and TMA simultaneously when inoculated into media containing substrate levels of these compounds. However, TMA-grown cells could not metabolize ['4C]DMS to '4CH4, although they could convert ['4C]methanol to '4CH4. These results suggest that metabolism of DMS proceeds along a somewhat different route than that of TMA and perhaps also that of methanol. The organism exhibited doubling times of 23 and 32 h for growth (25°C) in mineral media on TMA and DMS, respectively. Doubling times were more rapid (-6 h) when the organisms were grown on TMA in complex broth. In mineral media, the fastest growth on DMS occurred between pH levels of 7.0 and 8.7, at 29°C, and with 0.2 to 0.4 M Na+ and 0.04 M Mg2. Somewhat different results occurred for growth on TMA in complex broth. Cells had a moles percent G+C value of 44.5% for their DNA. Growth on DMS, TMA, and methanol yielded stable carbon isotope fractionation factors of 1.044, 1.037, and 1.063, respectively. Fractionation factors for hydrogen were 1.203 (DMS) and 1.183 (TMA).