Thermotogae Taxonomy
This phylum presently consists of a single class (Thermotogae), order (Thermotogales) and family (Thermotogaceae). It contains a total of nine genera (viz. Thermotoga, Petrotoga, Thermosipho, Fervidobacterium, Marinitoga, Kosmotoga, Geotoga, Thermopallium and Thermococcoides), all of which currently are part of the family Thermotogaceae. In the 16S rRNA trees the Thermotogae have been observed to branch with the Aquificae (another phylum comprising hyperthermophilic organisms) in close proximity to the archaeal-bacterial branch point. However, a close relationship of Thermotogae to Aquificae, and the deep branching of the latter group of species, is not supported by phylogenetic studies based upon other gene/protein sequences and also by conserved signature indels in several highly conserved universal proteins. The Thermotogae have also been scrutinized for their supposedly profuse Lateral gene transfer with Archaeal organisms. However, recent studies based upon more robust methodologies suggest that incidence of LGT between Thermotogae and other groups including Archaea is not as high as suggested in earlier studies.
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