cell variants in human physiology and pathology: A review.

(), initially isolated from human feces, has been recognised as a distinct taxon within the Archaea domain following comprehensive phenotypic, genetic, and genomic analyses confirming its uniqueness among methanogens. Its diversity, encompassing 15 genotypes, mirrors that of biotic and host-associated ecosystems in which plays a crucial role in detoxifying hydrogen from bacterial fermentations, converting it into mechanically expelled gaseous methane. In microbiota in contact with host epithelial mucosae, centres metabolism-driven microbial networks with , , , , , , , , whereas symbiotic association with the nanoarchaea Nanopusillus phoceensis determines small and large cell variants of . The former translocate with bacteria to induce detectable inflammatory and serological responses and are co-cultured from blood, urine, and tissular abscesses with bacteria, prototyping as a model organism for pathogenicity by association. The sources, mechanisms and dynamics of and lifespan acquisition, its diversity, and its susceptibility to molecules of environmental, veterinary, and medical interest still have to be deeply investigated, as only four strains of are available in microbial collections, despite the pivotal role this neglected microorganism plays in microbiota physiology and pathologies.