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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 µm for strain SWAN1^T 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 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. Na …