Methanomethylophilus alvi gen. nov., sp. nov., a novel hydrogenotrophic methyl-reducing methanogenic Archaea of the order Methanomassiliicoccales isolated from the human gut and proposal of the novel family Methanomethylophilaceae fam. nov Borrel, G. Fadhlaoui, K. Ben Hania, W. Gaci, N. Pehau-Arnaudet, G. Chaudhary, P. P. Vandekerckove, P. Ballet, N. Alric, M. O'Toole, P. W. /Fardeau, Marie-Laure /Ollivier, Bernard Brugère, J. F. archaea methanogens human gut microbiota Methanomassiliicoccales The methanogenic strain Mx-05(T) was isolated from the human fecal microbiome. A phylogenetic analysis based on the 16S rRNA gene and protein marker genes indicated that the strain is affiliated with the order Methanomassiliicoccales. It shares 86.9% 16S rRNA gene sequence identity with Methanomassiliicoccus luminyensis, the only member of this order previously isolated. The cells of Mx-05(T) were non-motile cocci, with a diameter range of 0.4-0.7 mu m. They grew anaerobically and reduced methanol, monomethylamine, dimethylamine, and trimethylamine into methane, using H-2 as an electron donor. H-2/CO2, formate, ethanol, and acetate were not used as energy sources. The growth of Mx-05(T) required an unknown medium factor(s) provided by Eggerthella lenta and present in rumen fluid. Mx-05(T) grew between 30 degrees C and 40 degrees C (optimum 37 degrees C), over a pH range of 6.9-8.3 (optimum pH 7.5), and between 0.02 and 0.34 mol.L-1 NaCl (optimum 0.12 mol.L-1 NaCl). The genome is 1.67 Mbp with a G+C content of 55.5 mol%. Genome sequence annotation confirmed the absence of the methyl branch of the H4MPT Wood-Ljungdahl pathway, as described for other Methanomassiliicoccales members. Based on an average nucleotide identity analysis, we propose strain Mx-05(T) as being a novel representative of the order Methanomassiliicoccales, within the novel family Methanomethylophilaceae, for which the name Methanomethylophilus alvi gen. nov, sp. nov. is proposed. The type strain is Mx-05(T) (JCM 31474T). 2023 text https://www.documentation.ird.fr/hor/fdi:010088750 fdi:010088750 Borrel G., Fadhlaoui K., Ben Hania W., Gaci N., Pehau-Arnaudet G., Chaudhary P. P., Vandekerckove P., Ballet N., Alric M., O'Toole P. W., Fardeau Marie-Laure, Ollivier Bernard, Brugère J. F.. Methanomethylophilus alvi gen. nov., sp. nov., a novel hydrogenotrophic methyl-reducing methanogenic Archaea of the order Methanomassiliicoccales isolated from the human gut and proposal of the novel family Methanomethylophilaceae fam. nov. 2023, 11 (11), 2794 [13 ] EN