Genomic and physiological characterization of 'Candidatus Methylocystis sumavensis', a novel acid-tolerant methanotroph from peatland

Methanotrophic bacteria in peatlands mitigate emissions of methane (CH ₄ ), a potent greenhouse gas. Yet, the identity, physiology, and adaptive traits of methanotrophs inhabiting acidic peatlands are still not fully characterised. Using classical enrichment methods and single-cell sorting, we isolated a novel bacterial methanotroph species from Czech peatland soil: ' Candidatus Methylocystis sumavensis'. ' Ca . M. sumavensis' is moderately acidotolerant, growing optimally at pH 6.8 and 24 – 37°C, with a CH ₄ oxidation rate of 14.2 ± 0.51 nmol CH ₄ µg protein ^-1 · hr ^-1 . The complete genome encodes two isozymes of particulate methane monooxygenase and genes providing the capacity for nitrous oxide reduction to di-nitrogen (N ₂ O). This suggests a potential role as a N ₂ O sink, possibly enabling the new species to oxidise CH ₄ under low-oxygen or anoxic conditions. The presence of four terminal oxidases, two of which are of a high-affinity type, and two different [NiFe]-hydrogenases (3b and a putative 4f group) suggests a capacity for diverse respiratory processes, likely including anaerobic metabolism. Several acid stress response systems, most strikingly a H ⁺ /Na ⁺ -translocating F-type ATP synthase in addition to a classical H ⁺ -translocating F-type ATP synthase, likely support survival in the isolates’ oligotrophic, acidic habitat. Our results reveal that the new methanotroph species combines unique metabolic traits, reflecting its adaptation to peat ecosystems and indicating a possible broader ecological role for peat-inhabiting methanotrophs beyond aerobic CH ₄ oxidation.