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

Abstract

Three thermophilic Methanothrix ("Methanosaeta") strains, strains PTT (= DSM 6194,) (T = type strain), CALS-1 (= DSM 3870), and 2-517 (= DSM 4774), were characterized chemotaxonomically and compared with five mesophilic strains, Methanothrix soehngenii ("Methanosaeta concifii") GP6 (= DSM 36711, Opfikon (= DSM 2139), FE (= DSM 3013), U,, and P,. These methanogens were exclusively acetotrophic and had a characteristic sheathed structure. The DNA base compositions of the strains which we studied ranged from 50.3 to 54.3 mol% guanine plus cytosine. The thermophilic strains often had phase-refractive gas vesicles inside their cells. Denaturing electrophoresis of proteins showed that the mesophilic and thermophilic Mefhanothrix strains formed two distinct groups and that there were differences in protein patterns between the groups. The difference between the thermophiles and mesophiles was also verified by comparing partial 16s rRNA sequences (ca. 30 base differences in ca. 540 bases). On the basis of our results, we propose the name Methanothrix thenophila for the three thermophilic strains. The type strain of M. thermophila is strain P, (= DSM 6194). We also propose that the name Methanothrix thenoacetophila ('LMethanosaeta thermoacetophila"), which was given to strain 2-517 (type strain), should be rejected because of its description, which was based on an enrichment culture, was inadequate.

Challenging Opinion 75

“…In contrast, Kamagata et al (1992) considered that Methanothrix thermoacetophila is not validly published and created the name Methanothrix thermophila in the knowledge that the type strain of that species is a member of the same genogroup as Methanothrix thermoacetophila 5Methanosaeta thermoacetophila. Furthermore, Kamagata et al (1992) 'reject' the name Methanothrix ('Methanosaeta') thermoacetophila.…”

“…Opinion 75 issued by the Judicial Commission (2008), dealing with the names Methanothrix Huser et al 1983, Methanothrix soehngenii Huser et al 1983, Methanothrix thermophila Kamagata et al 1992 and Methanosaeta thermophila, was the subject of discussions at both the Paris (2002) and San Francisco (2005) (Tindall et al, 2008) meetings of the Judicial Commission. Possible problems with the interpretation of the International Code of Nomenclature of Bacteria (the Code) were discussed at the meeting in San Francisco and it was agreed that the Opinion should be published as originally discussed and formulated, and that possible problems with the Opinion should be documented.…”

“…(ii) the type strains of Methanothrix thermoacetophila 5Methanosaeta thermoacetophila (Z-517) and Methanothrix thermophila (strain P T ) are known to be members of the same genogroup, and the wording of Kamagata et al (1992) is such that this may be interpreted to mean the same species.…”

“…Furthermore, Kamagata et al (1992) 'reject' the name Methanothrix ('Methanosaeta') thermoacetophila. However, 'only the Judicial Commission can place names on the list of rejected names (nomina rejicienda)' (see Rule 23a, Note 4, and Appendix 4, Rule 56a).…”

“…In studies on the type strains of the species Methanothrix soehngenii and Methanothrix thermoacetophila, Touzel et al (1988), Patel & Sprott (1990), Stackebrandt et al (1982) and Kamagata et al (1992) used either one or both of the type strains in their studies of protein patterns, DNA-DNA hybridization, G+C content and 16S rRNA gene sequencing, without addressing the question of whether the filament-forming methanogen described by the original authors could be 'critically identified'; in other words, they accepted the fact that they were dealing with data obtained from the methanogen. Patel & Sprott (1990), however, called into question the purity of strain Opfikon (the type of Methanothrix soehngenii) in order to create the new genus Methanosaeta, with Methanosaeta concilii as the type species.…”