Aquifex and hyperthermophilic phyla

Several hyperthermophilic species of Bacteria have been isolated that are phylogeneti- cally close to the hypothetical root of the tree of life in Figure 1. These isolates have been arranged into many distinct phyla containing only one or two genera like as Aquifex, Thermotoga, Methanopyrus and Pyrolobus all characterized through having optimal growth temperatures above 80∞C. This property coupled to the phylogenetic position of these Bacteria supports the notion that life starts at higher temperatures than we experience today.

Other phyla

The large diversity of the Bacteria is reflected in various other phyla which are not discussed here. These   include the   numerically abundant members of the   Flavobacteria as well as Cytophaga, Verrucomicrobia, green sulfur bacteria, Chloroflexus and Chlamydia.