Isolation and Characterization of New Methanothrix Strains

Abstract

Mesophilic Methanothrix sp. strains MTAS and MTKO were isolated as pure cultures from the sludge of anaerobic digestors. We examined the relationships between these two isolates and three other Methanothrix strains (strains Opfikon' [T = type strain], GP(il', and FE) by using an immunological method, by performing DNA homology experiments, and by analyzing polar lipids. Our results indicate that all five strains belong to the same species.Acetate is the precursor of at least 60% of the methane produced during anaerobic digestion of organic compounds (4, 20). Kaspar and Wiihrmann (13) reported that acetate splitting is the rate-limiting reaction in this system. On the other hand, the members of three genera, Methanothrix, Methanosaeta, and Methanosarcina, can convert acetate to methane. The members of the genus Methanothrix, in particular, have a high affinity for acetate (&, 0.7 mM), so these bacteria seem to play an important role in methane fermentation (8, 12).The genus Methanothrix includes two mesophilic species, Methanothrix soehngenii (type strain, Opfikon) (12) and Methanothrix concilii (type strain, GP6) (17). Touzel et al. indicated that strains OpfikonT (T =type strain) and GPGT belong to the same species, as judged by the results of DNA-DNA hybridization experiments, and proposed that the name Methanothrix concilii should be rejected as a later synonym of Methanothrix soehngenii (22). Recently, Patel i$nd Sprott proposed that the genus name Methanothrix should be rejected and described a new genus, Methanosaeta, with Methanosaeta concilii as its type species, because no axenic culture of Methanothrix soehngenii seems to exist ((18). In this paper we describe the isolation of two new Methanothrix strains as pure cultures (strains MTAS and MTKO), and we compare these strains with other Methanothrix strains. MATERIALS AND METHODS Sources of strains.Methanothrix concilii GP6T (= OCM69T) was obtained from the Oregon Collection of Methanogens, Beaverton. Methanothrix soehngenii Opfikon (= DSM 2139T) was a gift from A. J. B. Zehnder (Agricultural University, Wageningen, The Netherlands). Methanobacterium thermoautotrophicum AHT (= DSM 1053T), Methanosarcina barkeri MST (= DSM 800T), and Methanothrix soehngenii FE (= DSM 3013) were obtained from the Deutsche Sammulung von Mikroorganismen und Zellkulturen GmbH, Braunschweig, Federal Republic of Germany. Methanothrix sp. strain MTAS was isolated from the anaerobic digestor (in which the temperature is not controlled) that is used for treating domestic wastewater in the town of Ashiya (Fukuoka, Japan). Strain MTKO was isolated from the anaerobic fixed-bed digestor (in which the temperature is not controlled) that is used for treating wastewater from a flush toilet in our laboratory. * Corresponding author.Media and cultivation. We used Deutsche Sammlung von Mikroorganismen und Zellkulturen medium no. 334 (7) for isolating and cultivating all Methanothrix strains except strain GPtiT. This medium was dispensed into serum vials under 100% nitrogen atmosphere and ...

Methanogenesis from acetate: a comparison of the acetate metabolism in Methanothrix soehngenii and Methanosarcina spp.

“…Until the mid-seventies of this century, therefore, it was doubted that an organism could grow anaerobically on acetate [102]. Although up to now several organisms have been isolated which use acetate as sole energy source under anaerobic conditions, the problem of energy conservation in this process is not yet solved [26][27][28][29][30][31][32][33][34].…”

“…The bacterium was renamed Methanothrix soehngenii, with the Op- fikon strain as type strain [26][27][28]. Thereafter, several Methanothrix strains have been described, including the mesophilic Methanothrbc soehngenii strain FE, MTAS and MTKO and Methanothrix concilli GP-6 v nd the thermophilic strains Methanothrix CALS-1, PT and Methanothrlx thermoacetc~'~dla [29][30][31][32][33][34]. Although immunological studies with antisera showed only a weak relationship between the different Methanothrix species, Touzel unified the strains Opfikon, FE and GP-6 into one species, Methanothrix soehngenii, on the basis DNA-DNA hybridization studies [29,35].…”

Characterization of Three Thermophilic Strains of Methanothrix ("Methanosaeta") thermophila sp. nov. and Rejection of Methanothrix ("Methanosaeta") thermoacetophila

“…After this description, several mesophilic Methanothrix strains were isolated or "highly purified" (8,10,18,20,26). A thermophilic Methanothrix strain was first enriched from thermal lake mud by Nozhevnikova and Chudina (17), and these authors named their enriched organism (strain 2-517) Methanothrix thermoacetophila.…”

Comparison of acetate utilization among strains of an aceticlastic methanogen, Methanothrix soehngenii

“…Strain GP6 (OCM69) was from the Oregon Collection of Methanogens, Beaverton. Strains MTAS and MTKO were from our collection (9). Strain MTHI was isolated from an anaerobic sewage treatment plant in Hiagari, Kitakyushu, Japan.…”

“…Strain MTHI was isolated from an anaerobic sewage treatment plant in Hiagari, Kitakyushu, Japan. All strains were cultivated at 37°C in 1-liter serum vials that contained 500 ml of bicarbonate-free medium, the pH of which was controlled at 7.0 with 50 mM MES [2-(N-morpholino)ethanesulfonic acid] buffer (9). For cultivation of strain GP6, the medium was supplemented with 2 g of yeast extract per liter.…”