Expanding the cultivable human archaeome: Methanobrevibacter intestini sp. nov. and strain Methanobrevibacter smithii ‘GRAZ-2’ from human faeces

Two mesophilic, hydrogenotrophic methanogens, WWM1085 and <i>M. smithii</i> GRAZ-2, were isolated from human faecal samples. WWM1085 was isolated from an individual in the United States and represents a novel species within the genus <i>Methanobrevibacter. M. smithii</i> GRAZ-2 (=DSM 116045) was retrieved from a faecal sample of a European, healthy woman and represents a novel strain within this species. Both <i>Methanobrevibacter</i> representatives form non-flagellated, short rods with variable morphologies and the capacity to form filaments. Both isolates showed the typical fluorescence of F₄₂₀ and methane production. Compared to <i>M. smithii</i> GRAZ-2, WWM1085 did not accumulate formate when grown with H₂ and CO₂. The optimal growth conditions were at 35-39 °C and pH 6.5-7.5. Full genome sequencing revealed a genomic difference of WWM1085 to the type strain of <i>M. smithii</i> DSM 861 (=PS^T), with 93.55% average nucleotide identity (ANI) and major differences in the sequence of its <i>mcrA</i> gene (3.3% difference in nucleotide sequence). Differences in the 16S rRNA gene sequence were very minor, and thus distinction based on this gene marker might not be possible. <i>M. smithii</i> GRAZ-2 was identified as a novel strain within the species <i>Methanobrevibacter smithii</i> (ANI 99.04% to <i>M. smithii</i> DSM 861 [=PS^T]). Due to the major differences between WWM1085 and <i>M. smithii</i> type strain <i>M. smithii</i> DSM 861 (=PS^T) in phenotypic, genomic and metabolic features, we propose <i>Methanobrevibacter intestini</i> sp. nov. as a novel species with WWM1085 as the type strain (DSM 116060^T = CECT 30992^T).