DESCRIPTION OF THE KINGDOM CHLOROFLEXAE AND ITS SINGLE PHYLUM CHLOROFLEXOBACTERIA (BOTH FORMAL NAMES ARE DERIVED FROM GARRITY AND HOLT 2001)
| EUBACTERIA> PROTEOBACTERIAE> CHLOROFLEXAE> CHLOROFLEXOBACTERIA |
KINGDOM CHLOROFLEXAE LINKS
| Chloroflexae (klo-ro-FLEX-e) is a standization for this system from the phylum name, Chloroflexi (Garrity and Holt 2001 emend. Hugenholtz and Stackebrandt 2004). It is formed from a common genus, Chloroflexus, which is formed from a Greek and a Latin root meaning green (chloros χλοερός) and bend (flexus). The reference is to the green pigment in a filamentous organism that can bend and glide. |
| INTRODUCTION TO THE CHLOROFLEXAE AND ITS SINGLE PHYLUM, CHLOROFLEXOBACTERIA The Chloroflexae is a kingdom with a single phylum, Chloroflexobacteria and two classes: Chloroflexi and Thermomicrobia. The Chloroflexi are filamentous green non-sulfur bacteria that tolerate oxygen and have unique photosynthetic structures and accessory pigments. As photoautotrophs (text with tooltip) Phototrophs utilize light energy to provide metabolic energy. Sometimes this energy is stored asreduced organic compounds (food). , they fix CO2 using electrons from H2S or H2. Also, the carbon fixation pathway is unique in that CO2 combines with Acetyl CoA to make hydroxypropionate. Their cells contain pigmented, photosynthetic vesicles with plant-like carotenoids and chlorosomes (text with tooltip) Chlorosomes are thyllakoid-like structures. ( thylakoid (text with tooltip) Thylakoids are membranes, usually stacked, on which the photosynthetic pigments and enzymes are located. -like structures) that contain bacteriochlorophylls (text with tooltip) Bacteriochlorophylls are prokaryotic photosynthetic pigments that are related to chlorophylls of eukaryotes. . As facultative heterotrophs, they can use a variety of small organic compounds as food sources. Chloroflexi seem to be ubiquitous and have been found in open freshwater and open ocean (Figure 1). Typically, they grow as mats on aquatic sediments (marine and freshwater), and soil (Morris et al. 2004). Some taxa are tolerant of high temperatures and occur in hot springs (up to 70C). In addition they are common components of activated sludge in sewage treatment plants (Bjornsson et al. 2002). The filaments look and behave like small Oscillatoria (see the Cyanobacteria) or Beggiatoa (see the Saprospirae) in that they can glide when attached to surfaces. Herpetosiphon is a gliding filament that is bright yellow because, while it has accessory pigments like carotenes, lacks bacteriochlorophylls. Thus, it is not capable of photosynthesis. Quinn and Skerman (1980) described it as a scavenger that occasionally gangs up on microbial colonies and preys on them (Jurkevtich 2007, and Galperin 2008). Thermomicrobia is made of two very different genera: Thermomicrobium and Sphaerobacter. They are chemoheterotrophic, obligate aerobes, and cocci or short rods. Both taxa are found in high temperature waters. However, Sphaerobacter (Figure 2) is Gram positive and formerly placed in the Firmicutes (Phylum Actinobacteria) by Stackenbrandt et al. (1997) and Thermomicrobium had been placed in its own phylum by Garrity et al. (2001). Hugenholtz and Stackebrandt (2004) recently assembled this class and demonstrated that the two genera were in the same clade (Figure 3). We tentatively have the Chloroflexae in a clade that is basal to a crown group (Pirellae + Saprospirae + Chlorosulfatae and Spirochaetae + Proteobacteriae; see Figure 4). Once grouped with Chlorobia as the Green Non-Sulfur Bacteria, the Chloroflexus group was separated on the basis of its 16S rRNA. The current system was defined by Hugenholtz and Stackenbrandt (2004) in which Sphaerobacter was united with Thermomicrobium in a common class. Bergey’s Manual of Systematic Bacteriology, 2nd edition (Garrity et al. 2001) treats the taxa that we include in the Chloroflexae as the phyla B VI. “Chloroflexi” and B VII “Thermomicrobia”. Figure 5, which is a summary of the All Species Living Tree project (Yarza et al. 2008 and 2010; Munoz et al. 2011), shows the Chloroflexae as a sister to the Actinobacteria, a group that they removed from the Fimicutae. Until the systematics of this group stabilizes, we will keep the Chloroflexae as a separate kingdom with a single phylum. |
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| FIGURE 1. Chloroflexus, a gliding non-oxygenic photosynthetic bacterium. Image from http://microscope.mbl.edu/baypaul/microscope/images/t_imgAZ/chloroflexus_msw.jpg | FIGURE 2. An SEM micrograph of Sphaerobacter. Image from DOE, in the Public Domain |
FIGURE 3. A cladogram from Hugenholtz and Stackenbrandt (2004, Figure 1) that confirms the sister relationship between Sphaerobacter and Thermomicrobium and demonstrates an association with the Chloroflexi.
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 it differs significantly from Figure 5, a tree generated by the All Species Living Tree Project.
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 that the position of this group is in a clade together with the Actinobacteria, a group that they no longer include in the Firmicutes.
| 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. Galperin, M. Y. 2008. Social bacteria and asocial eukaryotes. Environmental Microbiology. 10(2): 281-288. 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. Garrity, G. M. and J. G. Holt. 2001. The road map to the Manual. In Bergey’s Manual of Systematic Bacteriology. 2nd ed. In: D. R. Boone, R. W. Castenholz, G. M. Garrity, eds. Springer. New York. pp. 119±166. Garrity, G. M., M. Winters, and D. Searles. 2001. Bergey’s manual of systematic bacteriology. 2nd ed. Springer-Verlag. New York. Holt, J. G., ed. 1989a. Other gram-negative bacteria, Cyanobacteria, Archaea. IN: Bergey’s manual of systematic bacteriology. Volume III. Williams and Wilkins. Baltimore, MD. Hugenholtz, P. and E. Stackenbrandt. 2004. Reclassification of Sphaerobacter thermophilus from the subclass Sphaerobacteridae in the phylum Actinobacteria to the class Thermomicrobia (emended description) in the phylum Chloroflexi (emended description). International Journal of Systematic and Evolutionary Microbiology. 54: 2049-2051. Jurkevitch, E. 2007. Predatory behaviors in bacteria—diversity and transitions. Microbe. 2: 67-73. Krieg, N. R. 1984. Gram-negative aerobic rods and cocci. In: Krieg, N. R. and J. G. Holt, eds. Bergey´s Manual of Systematic Bacteriology, Vol. 1: 140-408. 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. Quinn, G. R. and V. B. D. Skerman. 1980. Herpetosiphon – nature’s scavenger? Curr. Microbiol. 4: 57-62. Stackenbrandt, E., F. A. Rainey, and N. L. Ward-Rainey. 1997. Proposal for a newhierarchic classification system, Actinobacteria classis nov. Int. J. Sys. Bacteriol. 47: 479-491. 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 |
