| SYSTEMATIC BIOLOGY |
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| PHYLUM THERMOPLASMOBACTERIA | |||||
INTRODUCTION TO THE THERMOPLASMOBACTERIA
The thermoacidophils are quite distinctive as a group. They are unicellular but lack cell walls, giving them the appearance of microbial amebae (Figure A). Most have been found in association with hot (36-85C), sulfur-rich acidic conditions that occur in coal mine tailings. Obviously, they must occur in widely-scattered environments with the same characteristics across the globe (and deep underground?). Thermoacidophils have histones associated with the bacterial chromosome which may be the smallest of all the free-living bacteria. The cell membrane contains a lipopolysaccharide and glycoproteins (but no sterols) which allow it to be stable in extremely acidic (pH 1-3) environments.
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A. TEM micrograph of Thermoplasma. |
| Image taken from: http://www.biochem.mpg.de/baumeister/genome/home.html |
SYNOPTIC DESCRIPTION OF THE THERMOPLASMOBACTERIA
| The following description of the Thermoplasmobacteria came from Brock et al. (1994), Margulis and Schwartz (1998), Garrity et al. (2001 and 2003), and Black (2002). |
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I. SYNONYMS: Thermoacidophilic bacteria, archaebacterial mycoplasmas. II. PHYLUM CHARACTERISTICS: A. Structure Cell Form: Irregularly lobed. Cell Wall: Absent; gram-. Motility: Non-motile. B. Physiology O2 Tolerance: Aerobes. Substrates: Aerobic heterotrophic. Products: CO2, other products unknown. C. Other: Bacterial chromosome with histones; cell membrane contains a lipopolysaccharide and glycoproteins. D. Ecology: Grow in hot coal tailings; pH 1-3; 55-85C. |
SYSTEMATICS OF THE THERMOPLASMOBACTERIA
Margulis and Schwartz (1998) lump the all thermoacidophils together into a taxon called Crenarchaeota, which I treat as a kingdom. However, Garrity et al. (2001 and 2003) place the these organisms in a class Thermoplasmata within their phylum Euryarchaeota. I have followed the relative placement of Garrity et al. (2001) and moved them into the Kingdom Euryarchaeota together with the methanogens and extreme halophiles. I separated Thermoplasma and its relatives from other thermophiles because they are only mildly thermophilic, they do not contain sterols in their membranes, and they do contain histones in association with their chromosome.
HIERARCHICAL CLASSIFICATION OF THE THERMOPLASMOBACTERIA
| This system follows that of Garrity et al. (2001 and 2003) who place the thermoplasmas in the Euryarchaeota as a taxon equal to the methanogens and halophiles. I have done that. However, I have elevated the thermoplasmobacteria to phylum-level status. |
CLASS THERMOPLASMATAE
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This page is maintained by Jack R. Holt. Last revised: 02/07/2008.
