Methanobacterium paludis sp. nov. and a novel strain of Methanobacterium lacus isolated from northern peatlands

Abstract

Two mesophilic, hydrogenotrophic methanogens, designated strains SWAN1T and AL-21, were isolated from two contrasting peatlands: a near circumneutral temperate minerotrophic fen in New York State, USA, and an acidic boreal poor fen site in Alaska, USA, respectively. Cells of the two strains were rod-shaped, non-motile, stained Gram-negative and resisted lysis with 0.1 % SDS. Cell size was 0.6×1.5–2.8 µm for strain SWAN1T and 0.45–0.85×1.5–35 µm for strain AL-21. The strains used H2/CO2 but not formate or other substrates for methanogenesis, grew optimally around 32–37 °C, and their growth spanned through a slightly low to neutral pH range (4.7–7.1). Strain AL-21 grew optimally closer to neutrality at pH 6.2, whereas strain SWAN1T showed a lower optimal pH at 5.4–5.7. The two strains were sensitive to NaCl with a maximal tolerance at 160 mM for strain SWAN1T and 50 mM for strain AL-21. Na2S was toxic at very low concentrations (0.01–0.8 mM), resulting in growth inhibition above these values. The DNA G+C content of the genomes was 35.7 mol% for strain SWAN1T and 35.8 mol% for strain AL-21. Phylogenetic analysis of the 16S rRNA gene sequences showed that the strains are members of the genus Methanobacterium . Strain SWAN1T shared 94–97 % similarity with the type strains of recognized species of the genus Methanobacterium , whereas strain AL-21 shared 99 % similarity with Methanobacterium lacus 17A1T. On the basis of phenotypic, genomic and phylogenetic characteristics, strain SWAN1T ( = DSM 25820T = JCM 18151T) is proposed as the type strain of a novel species, Methanobacterium paludis sp. nov., while strain AL-21 is proposed as a second strain of Methanobacterium lacus .