Chloroflexus aurantiacus
554446
223014205
2008-07-02T04:55:31Z
200.112.71.14
{{Taxobox
| name = ''Chloroflexus aurantiacus''
| image = Chlorofl.jpg
| image_caption = ''Chloroflexus aurantiacus''
| regnum = [[Bacteria]]
| divisio = [[Chloroflexi]]
| classis = [[Chloroflexi]]
| ordo = [[Chloroflexales]]
| familia = [[Chloroflexaceae]]
| genus = [[Chloroflexus]]
| species = '''''C. aurantiacus'''''
| binomial = ''Chloroflexus aurantiacus''
}}
[[Image:Algae_on_left_bacteria_on_right_at_Norris_Geyser_Basin_in_Yellowstone-750px.JPG|thumb|250px|Thermophilic Organisms]]
'''''Chloroflexus aurantiacus''''' is a [[Photosynthesis|photosynthetic]] [[bacterium]] isolated from hot springs, belonging to the [[Chloroflexi|green non-sulfur bacteria]]. This organism is [[Thermophile|thermophilic]] and can grow at temperatures from 35 °C to 70 °C. ''Chloroflexus aurantiacus'' can survive in the dark if [[oxygen]] is available. When grown in the dark, ''Chloroflexus aurantiacus'' has a dark orange color. When grown in sunlight it is dark green. The individual bacteria tend to form filamentous colonies enclosed in sheaths, which are known as [[trichomes]].
==Physiology==
As a genus, ''Chloroflexus'' spp. are [[gram negative]] filamentous anoxygenic phototrophic (FAP) organisms that utilize [[photosystem II|type II]] photosynthetic reaction centers containing [[bacteriochlorophyll]] ''a'' similar to the [[purple bacteria]], and light-harvesting [[chlorosome|chlorosomes]] containing bacteriochlorophyll ''c'' similar to [[green sulfur bacteria]] of the ''Chlorobi''.
As the name implies, these anoxygenic phototrophs do not produce oxygen as a byproduct of photosynthesis, in contrast to oxygenic phototrophs such as [[cyanobacteria]], [[algae]], and higher [[plants]]. While oxygenic phototrophs use [[water]] as an [[electron donor]] for phototrophy, ''Chloroflexus'' uses reduced sulfur compounds such as [[hydrogen sulfide]], [[thiosulfate]], or elemental sulfur. This belies their antiquated name '''green non-sulfur bacteria''', however ''Chloroflexus'' spp. can also utilize [[hydrogen ]](H<sub>2</sub>) as a source of electrons.
''Chloroflexus aurantiacus'' is thought to grow [[photoheterotroph|photoheterotrophically]] in nature, but it has the capability of fixing inorganic carbon through [[photoautotroph|photoautotrophic]] growth. Instead of using the [[Calvin cycle|Calvin-Benson-Bassham Cycle]] typical of plants, ''Chloroflexus aurantiacus'' has been demonstrated to use a novel autotrophic pathway known as the [[3-hydroxypropionate pathway]].
The complete [[electron transport chain]] for ''Chloroflexus'' spp. is not yet known. Particularly, ''Chloroflexus aurantiacus'' has not been demonstrated to have a [[cytochrome bc1 complex|cytochrome ''bc<sub>1</sub>'' complex]], and may use different proteins to reduce [[cytochrome c|cytochrome ''c'']]
==Evolution of photosynthesis==
One of the main reasons for interest in ''Chloroflexus aurantiacus'' is in the study of the evolution of photosynthesis. As terrestrial mammals, we are most familiar with photosynthetic plants such as trees. However, photosynthetic eukaryotes are a relatively recent evolutionary development. Photosynthesis by eukaryotic organisms can be traced back to [[Endosymbiosis|endosymbiotic]] events in which non-photosynthetic [[eukaryote]]s internalized photosynthetic organisms. The [[chloroplast]]s of trees still retain their own DNA as a molecular remnant that indicated their origin as [[photosynthetic bacteria]].
===The "respiration early" hypothesis===
How did photosynthesis arise in bacteria? The answer to this question is complicated by the fact that there are several types of light-harvesting energy capture systems. ''Chloroflexus aurantiacus'' has been of interest in the search for origins of the so-called [[Photosystem II|type II]] [[photosynthetic reaction center]]. One idea is that bacteria with [[Cellular respiration|respiratory]] [[Electron transfer chain|electron transport]] "invented" photosynthesis by coupling a light-harvesting energy capture system to the pre-existing respiratory electron transport chain. Thus, rare organisms like ''Chloroflexus aurantiacus'' that can survive using either respiration or photosynthesis are of interest in on-going attempts to trace the [[evolution]] of photosynthesis. Shown below is an example of a "respiration early" theory in which ''Chloroflexus aurantiacus'' is a living example of the kind of organism that may have first developed photosynthesis based on [[chlorophyll]].
<div style="float:center;margin:0 0 1em 1em;">[[Image:Evolution of photosynthesis.png|Evolution of Photosynthesis]]</div>
==See also==
*[[Chloroflexi]]
*[[endosymbiotic theory]]
==References==
#1974 Article with report of the isolation of ''Chloroflexus aurantiacus''. NCBI PubMed entry: [http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=4374148 "A phototrophic gliding filamentous bacterium of hot springs, ''Chloroflexus aurantiacus'', gen. and sp. nov."]
#PubMed Article: [http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=6863222 "Temperature dependence of growth and membrane-bound activities of ''Chloroflexus aurantiacus'' energy metabolism"]
#PubMed Article: [http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=7275928 "Isolation and development of chlorosomes in the green bacterium ''Chloroflexus aurantiacus''"]
#NCBI PubMed Abstract: [http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=12367526 A cytochrome b origin of photosynthetic reaction centers: an evolutionary link between respiration and photosynthesis]
#NCBI PubMed Abstract: [http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=2246901 Evolutionary relationships between "Q-type" photosynthetic reaction centres: hypothesis-testing using parsimony]
# NCBI PubMed Abstract: [http://www.ncbi.nlm.nih.gov:80/entrez/query.fcgi?cmd=Retrieve&db=pubmed&dopt=Abstract&list_uids=8578586 Evolution of energetic metabolism: the respiration-early hypothesis]
{{Extremophile}}
[[Category:Extremophiles]]
[[Category:Microbiology]]
[[es:Chloroflexus aurantiacus]]
[[he:Chloroflexus]]