Figure 1.

Archaeal representatives associated to the human digestive tract. A simplified phylogeny of the Archaea (adapted from[89,148]) is shown. Taxonomic orders are drawn in filled square boxes, those composed of methanogens in yellow and others in light grey. Orders in which some members have been found in the human digestive tract are indicated in light blue boxes when identified by sequences derived from nested-PCR (or deep sequencing on low yield amplifications for Nitrososphaera spp.) or a limited number of studies, and other are indicated in dark blue boxes in which abundant and recurrently reported species are mentioned in orange boxes or light blue when observed from limited number of studies. For the Methanomassiliicoccales (¹), also referred as Methanoplasmatales in the literature, the repartition of Methanomassiliicoccus spp. and Ca. Methanomethylophilus spp. in two different clades is highlighted by yellow branches (see the text for details).