Chlorobium

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NCBI:
Taxonomy
/>Genome

Electron micrograph of Chlorobium tepidum. Ovoid chlorosomes can be seen attached to the cytoplasmic membrane. From CyanoBase.
Light micrograph of Chlorobium tepidum. From CyanoBase.


Classification

Higher order taxa:

Bacteria; Bacteroidetes/Chlorobi group; Bacteroidetes; Chlorobi; Chlorobia; Chlorobiales; Chlorobiaceae

Species:

Chlorobium ferrooxidans, Chlorobium limicola, Chlorobium phaeobacteroides, Chlorobium phaeovibraoides, Chlorobium sp.

Description and Significance

Chlorobium tepidum is a thermophilic green sulfer bacteria originally isolated from a New Zealand hot spring. This type of bacterium has special light-harvesting complexes called chlorosomes that contain bacteriochlorophylls and carotenoids. Chlorobium grows in dense mats over hot springs as well as in other warm muds and bodies of water that contain sufficient hydrogen sulfide (used by C. tepidum as an elecron donor). C. tepidum is a valuable model for the green sulfur bacteria because it is easily cultivated and naturally transformable.

Genome Structure

The genome of C. tepidum's single circular chromosome is 2,154,946 bp and was the first sequenced in the phylum Chlorobia. Many genes were found to be highly conserved among photosynthetic species and seemed to have no clear function within C. tepidum; however, these genes are thought to play specific roles in photosynthesis or photobiology. Phylogenomic analysis and comparison showed that ''C. tepidum '' contains duplications of genes involved in biosynthetic pathways for photosynthesis and the metabolism of sulfer and nitrogen. These methods also displayed genetic similarities between ''C. tepidum '' metabolic processes and many Archaeal species (Eisen ''et al''. 2002). There are three other species that are currently being sequenced and are in the assembly process. They are Chlorobium phaeobacteroides DSM 266, Chlorobium phaeobacteroides BS1, Chlorobium limicola DSM 245. ==Cell Structure and Metabolism== ''Chlorobium ''are Gram-negative cells. ''Chlorobium ''sp. can from long chains of almost spherical cells. Some strains can form coils of C-shaped cells. ''Chlorobium tepidum'' lives by anoxygenic photosynthesis and produces elemental sulfur as a waste product. ''C. tepidum'' deposits the elemental sulfer outside its cells unlike ''Chromatium'' and ''Thiothrix'', two other sulfer-producing bacteria. In addition, they can photooxidize hydrogen as well as other sulfur compounds like sulfide, polysulfide, and thiosulfate. They are also obligatory autotrophic. The major light-harvesting antenna organelle, which uses electromagnetic energy to power these processes, in ''''C. tepidum'''' is the chlorosome, which consists of highly aggregated bacteriochlorophyll c and carotenoids surrounded by a lipid-protein envelope. This ovoid structure is different from most other phototrophic organisms. (However, they are similar to a structure contained within the phylogenetically distant family ''Chloroflexaceae''.) The chlorosomes are 70 to 180 nm long and 30 to 60 nm wide. As can be seen on the picture at the [http://biology.kenyon.edu/Microbial_Biorealm/bacteria/bacteroidete_chlorob_group/Chlorobium/chlorobium_wiki.htm#top top] of this page, they are attached to the reactions centers in the cytoplasmic membrane. Oxidation of sulfide to sulfur has been studied in the past in ''C. limicola'' as a possible biocatalyst to remove acid gases made by the hydroprocessing of fossil fuels. The formation of sulfur from sulfide, in which sulfide acts as the reducing substrate, appears as follows (Douglas, ''et al''. 1985): [[Image:sulfur_formulas|frame|center|]] To see a list of some of the metabolic pathways that occur within ''C. tepidum'', visit [http://www.systems-biology.org/001/kegg/cte.html The Systems Biology Institute] or visit a list of the genes that control known metabolic pathways at [http://www.kazusa.or.jp/cyano/Chlorobium/cgi-bin/category_ch.cgi?comp=A6B2CB2A9 Cyanobase. ] ==Ecology== ''C. tepidum'' is a green sulfur bacterium that generally grows in a dense mat over hot springs. They are also found in anoxic and sulfide-rich waters, mud, and sediments. They grow best at tempuratures between 40 and 50 degrees Celsius and at a pH between 6.0 and 4.5. The phototrophic bacterial composition of a bacterial mat or in any body of water is usuallly dependent on what quality and wavelength of light that the water recieves. Factors that effect this are algae that filter the light and the terrain surrounding the hot spring, mud, or body of water. Bacteria of different pigments capture different wavelengths of light; therefore, ''Chlorobium'' and other green sulfur bacteria like ''Chromotium'', as well as other phototrophic bacteria, can be found distributed throughout their environment in a way that allows them to survive and efficiently compete with one another. In addition to the quality of light, ''C. tepidum'' and other green sulfur bacteria require sufficient amounts of hydrogen sulfide or other such electron donors for their unique photosynthetic pathways (Montesinos ''et al''.1983) . Because of ''C. tepidum'''s ability to grow in low light and oxygen (during the early days of the earth when there were high levels of U.V light) researchers believe that this is where photosythesis may have its origins. [[Image:chlorobium_yellowstone|frame|right|Microbial mats in Yellowstone National park shown to contain Chlorobium tepidum through reflectance spectroscopy. From the [http://www.lpi.usra.edu/education/EPO/yellowstone2002/workshop/tbvspring2/ Lunar and Planetary Institute.]]] ==References== [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=238392 Cork, Douglas, Jeremy Mathers, Andrea Maka, and Anna Srnak. 1985. "Control of oxidative sulfer metabolism of ''Chlorobium limicola'' forma ''thiosulfatophilum''." ''Applied and Environmental Microbiology, ''Vol. 49, No. 2. American Society for Microbiology. 269-272. ] [http://www.kazusa.or.jp/cyano/Chlorobium/about.html CyanoBase: About ''Chlorobium tepidum ''] [http://www.pnas.org/cgi/content/abstract/99/14/9509 Eisen, Jonathan A., ''et al''. 2002. "The complete genome sequence of'' Chlorobium tepidum TLS'', a photosynthetic, anaerobic, green-sulfur bacterium." Proc Natl Acad Sci USA, Vol. 99, No. 14. 9509-9514. ] [http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=239512 Montesinos, Emilio, Ricardo Guerrero, Carlos Abella, and Isabel Esteve. 1983. "Ecology and physiology of the competition for light between ''Chlorobium limicola'' and ''Chlorobium phaeobacteroides'' in natural habitats." ''Applied and Environmental Microbiology'', Vol. 46, No. 5. American Society for Microbiology. 1007-1016. ] [http://www.bmb.psu.edu/faculty/bryant/lab/chlorobiumtepidum/ PennState: Research on ''Chlorobium tepidum ''in the Bryant laboratory ] [http://141.150.157.117:8080/prokPUB/index.htm The Prokaryotes: An Evolving Electronic Resource for the Mircobiological Community. 2004. Springer-Verlag New York, LLC].