DESCRIPTION OF THE KINGDOM THERMOTOGAE AND ITS SINGLE PHYLUM THERMOTOGOBACTERIA
| EUBACTERIA> PROTEOBACTERIAE> THERMOTOGAE> THERMOBACTERIA |
KINGDOM THERMOTOGAE LINKS
| Thermotogae (ther-mo-TO-ge) is derived from a Greek root meaning hot (thermos -θερμός) and a Latin root for the garment of a Roman citizen (toga). The name is derived from Thermotoga, a common genus in the group. It also is descriptive of the kingdom in that many taxa inhabit hot springs and deep ocean vents, and have a specialized outer covering called a toga (text with tooltip) A toga is a specialized membrane-like outer cell covering that occurs in the Thermotogae. This does not seem to be homologous to the outer membranes of Gram negative bacteria. . |
| INTRODUCTION TO THE KINGDOM THERMOTOGAE AND ITS SINGLE PHYLUM THERMOTOGOBACTERIA Thermotogae had been observed and described from a hot sulfur spring in Yellostone at the beginning of the 20th Century (Setchell 1903). However, the unique status of the group was not recognized until almost 90 years later when Huber et al. (1992) demonstrated that Aquifex occupied a distinct basal clade within the Eubacteria according to its 16S rRNA sequences. All taxa within this phylum are unicellular rods. However, the thermotogae are made up of two distinct groups (two classes in this system). One group, characterized by Aquifex (Figure 1), is motile and has groups of polar flagella. The Thermotoga (Figure 2) group is characterized by the occurrence of an outer covering called a toga that is several times thicker than the cell wall. The thermotogae occur in deep ocean vents and other hot springs areas, some with temperatures approaching the boiling point (to 95C, Deckert et al. 1998, Reysenbach et al. 2000). This was only a curiosity when first reported by Setchell in 1903. However, after Huber and Setter (1998) made the case for the importance of hyperthermophiles to biotechnology applications, their strains became sought after and patentable. Physiologically, they tend to be strict anaerobes though Aquifex (Figure 1) oxidizes H2, S0, or thiosulfate with O2 (microaerophilic) or NO3- (Deckert et al. 1998). In general, they are fermenters of of sugars, proteins, and other organic compounds. That they manage to carry out such a broad range of physiology in high temperature environments is interesting but made remarkable considering that the genome of Aquifex is only about one-third that of E. coli (Deckert et al. 1998). Another surprise offered by an examination of the Thermotoga genome (Mongodin et al. 2005) is a large number of recognizable archaean genes, which, presumably, represent lateral gene transfer events. That may also be an explanation for why the structure of fucosidase, an enzyme that breaks down certain long-chain carbohydrates, in Thermotoga (Figure 2) is more like that of animals than of other eubacteria (Sulzenbacher et al. 2004). The Aquifex and Thermotoga groups may not be associated in a monophyletic clade. Reysenbach et al. (2000) showed that the Aquifex clade was a sister to Thermotoga + the rest of the Eubacteria (Figure 3). If so, Aquifexi and Thermotogiae would have to be separated into distinct groups (kingdoms?). Much more convincing evidence would have to be forthcoming, though. We follow the moderately conservative view proposed by Margulis and Schwartz (1998) in which the taxa occupy a separate phylum (Thermotogae; B-14). Bergey’s Manual of Systematic Bacteriology, 2nd edition (Garrity et al. 2001) treats the taxa that we include in the Thermotogae as two phyla (BI and BII). In most analyses (see Figures 4 and 5), the Thermotogae emerge as sisters to the rest of the Eubacteria. |
 |  |
| FIGURE 1. A TEM micrograph of Aquifex showing the polar flagella. Image from http://biology.kenyon.edu/Microbial_Biorealm/bacteria/aquifex/aquifex.htm | FIGURE 2. A TEM micrograph of Thermotoga with its outer covering or toga. Image from http://www.jcsg.org/images/targets/thermotoga.jpg |
FIGURE 3. This is from Reysenbach et al (2000). They examined the 16S rRNA microbial diversity in Calcite Springs, Yellowstone National Park. The outgroup is archaeal. The clade Hydrogenobacter – GAN1-4 is a sister to the rest of the Eubacteria, which includes Thermotoga+Fervidobacterium. Thus, calling into question the monophyly of the Thermotogae.
FIGURE 4. This tree uses Margulis and Schwartz (1998), with modifications from Garrity et al. (2001, 2003, and 2005), Tudge (2000), and Black (2002) in its structure. Note that, although it differs significantly from Figure 5, a tree generated by the All Species Living Tree Project, Thermotogae occupies a basal position in both.
FIGURE 5. A simplified summary tree for the Eubacteria adapted from the All Species Living Tree Project (Yarza et al. 2008 and 2010; Munoz et al. 2011). Note the basal position of the Thermotogae.
| FURTHER READING: DISCOVERY OF THE DOMAINS OF LIFE INTRODUCTION TO THE DOMAIN EUKARYA DESCRIPTION OF THE DOMAIN ARCHAEA |
| LITERATURE CITED Barnes, R. S. K. 1984b. Kingdom Monera. IN: Barnes, R.S.K., ed. A synoptic classification of living organisms. Sinauer Associates. Sunderland, Mass. Black, J. G. 2002. Microbiology, Principles and Explorations. 5th ed. John Wiley and Sons, Inc. New York. Brock, T. D., M.T. Madigan, J.M. Martinko, and J. Parker. 1994. Biology of Microorganisms. 7th ed. Prentice Hall. Englewood Cliffs, NJ. Deckert, G., P. V. Warren, T. Gaasterland, W. G. Young, A. L. Lenox, D. E. Graham, R. Overbeek, M. A. Snead, M. Keller, M. Aujay, R. Huber, R. A. Feldman, J. M. Short, G. J. Olsen, and R. V. Swanson. 1998. The complete genome of the hyperthermophilic bacterium Aquifex aeolicus. Nature. 392: 353-363. Garrity, G. M., M. Winters, and D. Searles. 2001. Bergey’s manual of systematic bacteriology. 2nd ed. Springer-Verlag. New York. Garrity, G. M., J. A. Bell, and T. G. Lilburn. 2003. Taxonomic Outline of the Prokaryotes. Bergey’s Manual of Systematic Bacteriology. 2nd edition. Release 4.0. Springer-Verlag. New York. pp. 1-397. Huber, R., T. Wilharm, D. Huber, A., Trincone, A., S. Burggraf, H. König, R. Rachel, I. Rockinger, H. Fricke, and K. O. Stetter. 1992. Aquifex pyrophilus gen. nov. sp. nov., represents a novel group of marine hyperthermophilic hydrogen-oxidizing bacteria. Syst. Appl. Microbiol. 15: 340–351. Margulis, L. and K. Schwartz. 1998. Five kingdoms, an illustrated guide to the phyla of life on earth. 3nd Edition. W. H. Freeman and Co. New York. Mongodin, E. F., I. R. Hance, R. T. DeBoy, S. R. Gill, S. Daugherty, R. Huber, C. M. Fraser, K. Stetter, and K. E. Nelson. 2005. Gene transfer and genome plasticity in Thermotoga maritima, a model hyperthermophilic species. Journal of Bacteriology. 187(14): 4935-4944. Reysenbach, L., G. S. Wickham, and N. R. Pace. 1994. Phylogenetic analysis of the hyperthermophilic pink filament community in Octopus Spring, Yellowstone National Park. Appl. Environ. Microbiol. 60: 2113–2119. Setchell, W. A. 1903. The upper temperature limits of life. Science. 17: 934–937. Sulzenbacher, G., C. Bignon, T. Nishimura, C. A. Tarling, S. G. Withers, B. Henrissat, and Y. Bourne. 2004. Crystal structure of Thermatoga maritima α-l-Fucosidase, insights into the catalytic mechanism and the molecular basis for fucosidosis. Journal of Biological Chemistry. 279: 13119-13128. Tudge, C. 2000. The Variety of Life, A Survey and a Celebration of all the Creatures That Have Ever Lived. Oxford University Press. New York. |
| By Jack R. Holt. Last revised: 02/15/2015 |
