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

Two mesophilic, hydrogenotrophic methanogens, designated strains SWAN1^T 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 mm for strain SWAN1^T and 0.45-0.85 ×1.5-35 mm for strain AL-21. The strains used H₂/CO₂ but not formate or other substrates for methanogenesis, grew optimally around 32-37 6C, 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 SWAN1^T 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 SWAN1^T 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 SWAN1^T 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 SWAN1^T 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 SWAN1^T (5DSM 25820T5JCM 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.