DESCRIPTION OF THE PHYLUM APHRAGMABACTERIA (MARGULIS AND SCHWARTZ 1982)
| EUBACTERIA> FIRMICUTAE> APHRAGMOBACTERIA |
PHYLUM APHRAGMABACTERIA LINKS
| Aphragmabacteria (pronounced a- FRAG-muh-bak-TE-re-uh) is formed from three Greek roots that mean “without” (a -ἀ-) “fence or barrier” (phraktes -φράκτης) and “little stick” (bakterion -βακτήριον). The reference is to the absence of a cell wall in this group. |
| INTRODUCTION TO THE APHRAGMOBACTERIA Commonly called mycoplasmas, these are tiny irregularly-lobed ameba-like cells that live as intracellular parasites of many different animals, plants, and protists. As such, they are the smallest cellular organisms on earth with a range in size of 0.3-0.5 µm and a genome of 580-2200 kb (Fraser, et al. 1995). Likely, the parasitic existence allowed them to lose the typical bacterial wall and become among the most reduced of the bacteria (Himmelreich et al. 1996). The minimalist genome may help offer some insight into basic machinery of a self-replicating cell (Razin et al. 1998). Mycoplasmas tend to be anaerobes and Chemoheterotrophs (text with tooltip) Chemolithotrophs are autotrophs (make their own food) by using inorganic sources for energy and reducing power to fix carbon dioxide into food. or fermentive heterotrophs. A consequence of their reduced genome is that they require sterols (text with tooltip) Sterols are ubiquitous as components of membranes in eukaryotes and a few prokaryotes. Cholesterol is a common animal sterol. which they incorporate into their cell membranes (only Acholeplasma does not). They multiply by binary fission and, when colonies are grown on solid media, have a “fried egg appearance.” Several mycoplasma diseases afflict humankind. One is Mycoplasma pneumoniae, the causative agent of a disease of the upper and lower respiratory tracts. Figure 1 shows mycoplasmas attached to the cilia of a swine trachea. In the lungs, they can cause an acute type of pneumonia against which antibiotics are only marginally effective. Spiroplasma (Figure 2) is an intracellular parasite of arthropods and plants. This system is a modification of Margulis and Schwartz (1998) in which the phylum includes all bacteria that lack walls; however, with that as the sole criterion, they include many taxa (e.g. Ehrlichia) that are rickettsias and belong in the Proteobacteriae. Brock and Madigan (1988) suggest that the mycoplasms are divided into 2 major groups according to their sterol requirement. Bergey’s Manual of Systematic Bacteriology, volume 1, section 10 (Holt 1984) treats the mycoplasmas as very different from the other bacteria. Holt (1984) places them into their own division (phylum) called Tenericutes. Unfortunately, he lumps all bacteria without cell walls into the same taxon; therefore, Thermoplasma is treated as a mycoplasma. Bergey’s Manual of Systematic Bacteriology, 2nd edition (Garrity et al. 2001 and 2003) treats the taxa that we include in the Aphragmabacteria as a class of phylum Firmicutes (BXIII). Indeed, they seem to be clostridia without walls. The All Species Living Tree Project (Yarza et al. 2008 and 2010; Munoz et al. 2011) suggests a complex arrangement of the taxa within the Aphragmabacteria, some having affiliations with the Firmicutes and others elevated to a group equivalent to the Firmicutes. |
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| FIGURE 1. Mycoplasma attached to cilia in swine respiratory tract (TEM micrograph). Image from http://biology.kenyon.edu/Microbial_Biorealm/bacteria/gram-positive/mycoplasma/Mhyo_cilia.gif | FIGURE 2. Spiroplasma, a plant pathogen (SEM micrograph). Image from http://www.apsnet.org/education/IllustratedGlossary/PhotosS-V/spiroplasma.jpg |
FIGURE 3. Tentative relationships between the phyla of the Firmicutes that we use in this system. The tentative location of the mycoplasmas is indicated by the shaded box. 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.
| 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. and M. T. Madigan. 1984. Biology of Microorganisms. 5th ed. Prentice Hall. Englewood Cliffs, NJ. Brock, T. D., M. T. Madigan, J. M. Martinko, and J. Parker. 1994. Biology of Microorganisms. 7th ed. Prentice Hall. Englewood Cliffs, NJ. Fraser, C. M., J. D. Gocayne, O. White, M. D. Adams, R. A. Clayton, R. D. Fleischmann, C. J. Bult, A. R. Kerlavage, G. Sutton, J. M. Kelley, J. L. Fritchman, J. F. Weidman, K. V. Small, M. Sandusky, J. Fuhrmann, D. Nguyen, T. R. Utterback, D. M. Saudek, C. A. Phillips, J. M. Merrick, J.-F. Tomb, B. A. Dougherty, K. F. Bott, P.-C. Hu, T. S. Lucier, S. N. Peterson, H. O. Smith, C. A. Hutchison III, and J. C. Venter. 1995. The minimal gene compliment of Mycoplasma genitalium. Science. 270(5235): 397-404. 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. Himmelreich, R., H. Hilbert, H. Plagens, E. Pirkl, B.-C. Li, and R. Hermann. 1996. Complete analysis of the genome of the bacterium Mycoplasma pneumoniae. Nucleic Acids Research. 24(22): 4420-4449. Holt, J. G. ed. 1984. Gram-negative bacteria of medical or industrial importance. IN: Bergey’s manual of systematic bacteriology. Volume I. Williams and Wilkins. Baltimore, MD. [L] Margulis, L. and K. Schwartz. 1988. Five Kingdoms, An Illustrated Guide to the Phyla of Life on Earth. 2nd Edition. W. H. Freeman and Co. New York. Margulis, L. and K. Schwartz. 1998. Five Kingdoms, An Illustrated Guide to the Phyla of Life on Earth. 3rd Edition. W. H. Freeman and Co. New York. Razin, S., D. Yogev, and Y. Naot. 1998. Molecular biology and pathogenicity of mycoplasmas. Microbiology and Molecular Biology Reviews. 62(4): 1094-1156. 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: 02/11/2013 |
