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''Chloroflexus aurantiacus'' is a
photosynthetic bacterium
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were amon ...
isolated from hot springs, belonging to the
green non-sulfur bacteria
The Chloroflexia are a class of bacteria in the phylum Chloroflexota, known as filamentous green non-sulfur bacteria. They use light for energy and are named for their green pigment, usually found in photosynthetic bodies called chlorosomes.
Chl ...
. This organism is
thermophilic
A thermophile is an organism—a type of extremophile—that thrives at relatively high temperatures, between . Many thermophiles are archaea, though they can be bacteria or fungi. Thermophilic eubacteria are suggested to have been among the earl ...
and can grow at temperatures from 35 °C to 70 °C (94.998 to 158 °F). ''Chloroflexus aurantiacus'' can survive in the dark if
oxygen
Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as ...
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
Trichomes (); ) are fine outgrowths or appendages on plants, algae, lichens, and certain protists. They are of diverse structure and function. Examples are hairs, glandular hairs, scales, and papillae. A covering of any kind of hair on a plant ...
.
Physiology
As a genus, ''Chloroflexus'' spp. are filamentous anoxygenic phototrophic (FAP) organisms that utilize
type II photosynthetic reaction centers containing
bacteriochlorophyll
Bacteriochlorophylls (BChl) are photosynthetic pigments that occur in various phototrophic bacteria. They were discovered by C. B. van Niel in 1932. They are related to chlorophylls, which are the primary pigments in plants, algae, and cyanoba ...
''a'' similar to the
purple bacteria
Purple bacteria or purple photosynthetic bacteria are Gram-negative proteobacteria that are phototrophic, capable of producing their own food via photosynthesis. They are pigmented with bacteriochlorophyll ''a'' or ''b'', together with various ...
, and light-harvesting
chlorosome
A chlorosome is a photosynthetic antenna complex found in green sulfur bacteria (GSB) and some green filamentous anoxygenic phototrophs (FAP) ( Chloroflexaceae, Oscillochloridaceae; both members of Chloroflexia). They differ from other antenna ...
s containing bacteriochlorophyll ''c'' similar to
green sulfur bacteria
The green sulfur bacteria are a phylum of obligately anaerobic photoautotrophic bacteria that metabolize sulfur.
Green sulfur bacteria are nonmotile (except ''Chloroherpeton thalassium'', which may glide) and capable of anoxygenic photosynthe ...
of the ''
Chlorobiota
The green sulfur bacteria are a phylum of obligately anaerobic photoautotrophic bacteria that metabolize sulfur.
Green sulfur bacteria are nonmotile (except ''Chloroherpeton thalassium'', which may glide) and capable of anoxygenic photosynthes ...
''. Like other members of its phylum (''cf.''
Chloroflexota
The Chloroflexota are a phylum of bacteria containing isolates with a diversity of phenotypes, including members that are aerobic thermophiles, which use oxygen and grow well in high temperatures; anoxygenic phototrophs, which use light for phot ...
), the species stains
Gram negative
The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram.
Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to th ...
, yet has a single lipid layer (monoderm),
but with thin
peptidoglycan
Peptidoglycan or murein is a unique large macromolecule, a polysaccharide, consisting of sugars and amino acids that forms a mesh-like peptidoglycan layer outside the plasma membrane, the rigid cell wall (murein sacculus) characteristic of most ba ...
, which is compensated for by
S-layer protein.
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
Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae exclude ...
. While oxygenic phototrophs use
water
Water (chemical formula ) is an Inorganic compound, inorganic, transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living ...
as an
electron donor
In chemistry, an electron donor is a chemical entity that donates electrons to another compound. It is a reducing agent that, by virtue of its donating electrons, is itself oxidized in the process.
Typical reducing agents undergo permanent chemi ...
for phototrophy, ''Chloroflexus'' uses reduced sulfur compounds such as
hydrogen sulfide,
thiosulfate
Thiosulfate ( IUPAC-recommended spelling; sometimes thiosulphate in British English) is an oxyanion of sulfur with the chemical formula . Thiosulfate also refers to the compounds containing this anion, which are the salts of thiosulfuric acid, ...
, or elemental sulfur. This belies their obsolescent name green non-sulfur bacteria; however, ''Chloroflexus'' spp. can also utilize
hydrogen
Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...
(H
2) as a source of electrons.
''Chloroflexus aurantiacus'' is thought to grow
photoheterotroph
Photoheterotrophs ('' Gk'': ''photo'' = light, ''hetero'' = (an)other, ''troph'' = nourishment) are heterotrophic phototrophs – that is, they are organisms that use light for energy, but cannot use carbon dioxide as their sole carbon source. Con ...
ically in nature, but it has the capability of fixing inorganic carbon through
photoautotroph Photoautotrophs are organisms that use light energy and inorganic carbon to produce organic materials. Eukaryotic photoautotrophs absorb energy through the chlorophyll molecules in their chloroplasts while prokaryotic photoautotrophs use chlorophyl ...
ic growth. Instead of using the
Calvin-Benson-Bassham Cycle typical of plants, ''Chloroflexus aurantiacus'' has been demonstrated to use an autotrophic pathway known as the
3-Hydroxypropionate pathway
The 3-Hydroxypropionate bicycle, also known as the 3-Hydroxypropionate pathway, is a process that allows some bacteria to generate 3-Hydroxypropionate utilizing carbon dioxide. In this pathway CO2 is fixed (i.e. incorporated) by the action of two ...
.
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, and may use different proteins to reduce
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
endosymbiotic
An ''endosymbiont'' or ''endobiont'' is any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship.
(The term endosymbiosis is from the Greek: ἔνδον ''endon'' "within ...
events in which non-photosynthetic
eukaryotes internalized photosynthetic organisms. The
chloroplasts of trees still retain their own DNA as a molecular remnant that indicated their origin as
photosynthetic bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of prokaryotic microorganisms. Typically a few micrometr ...
.
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
type II photosynthetic reaction center
A photosynthetic reaction center is a complex of several proteins, pigments and other co-factors that together execute the primary energy conversion reactions of photosynthesis. Molecular excitations, either originating directly from sunlight or t ...
. One idea is that bacteria with
respiratory
The respiratory system (also respiratory apparatus, ventilatory system) is a biological system consisting of specific organs and structures used for gas exchange in animals and plants. The anatomy and physiology that make this happen varies gre ...
electron transport
An electron transport chain (ETC) is a series of protein complexes and other molecules that transfer electrons from electron donors to electron acceptors via redox reactions (both reduction and oxidation occurring simultaneously) and couples thi ...
evolved 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
Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
of photosynthesis.
See also
*
Chloroflexota
The Chloroflexota are a phylum of bacteria containing isolates with a diversity of phenotypes, including members that are aerobic thermophiles, which use oxygen and grow well in high temperatures; anoxygenic phototrophs, which use light for phot ...
*
endosymbiotic theory
References
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Further reading
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External links
Type strain of ''Chloroflexus aurantiacus'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
{{Taxonbar, from=Q2473850
Phototrophic bacteria
Bacteria described in 1974
Chloroflexota