Chloroflexus aurantiacus is a photosynthetic

Photosynthesis

Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...

 bacterium isolated from hot springs, belonging to the green non-sulfur bacteria

Chloroflexi

Chloroflexi is one of four classes of bacteria in the phylum Chloroflexi, known as filamentous green non-sulfur bacteria. They produce energy from light and are named for their green pigment, usually found in photosynthetic bodies called chlorosomes....

. This organism is thermophilic

Thermophile

A thermophile is an organism — a type of extremophile — that thrives at relatively high temperatures, between 45 and 122  °C . Many thermophiles are archaea...

 and can grow at temperatures from 35 °C to 70 °C. Chloroflexus aurantiacus can survive in the dark if oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 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 type II

Photosystem II

Photosystem II is the first protein complex in the Light-dependent reactions. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. The enzyme uses photons of light to energize electrons that are then transferred through a variety of coenzymes and cofactors to reduce...

 photosynthetic reaction centers containing bacteriochlorophyll

Bacteriochlorophyll

Bacteriochlorophylls are photosynthetic pigments that occur in various phototrophic bacteria. They were discovered by Von Neil in 1932 . They are related to chlorophylls, which are the primary pigments in plants, algae, and cyanobacteria. Groups that contain bacteriochlorophyll conduct...

 a similar to the purple bacteria

Purple bacteria

Purple bacteria or purple photosynthetic bacteria are proteobacteria that are phototrophic, that is capable of producing energy through photosynthesis...

, and light-harvesting chlorosome

Chlorosome

A Chlorosome is a photosynthetic antenna complex found in green sulfur bacteria and some green filamentous anoxygenic phototrophs . They differ from other antenna complexes by their large size and lack of protein matrix supporting the photosynthetic pigments...

s containing bacteriochlorophyll c similar to green sulfur bacteria

Green sulfur bacteria

The green sulfur bacteria are a family of obligately anaerobic photoautotrophic bacteria. Most closely related to the distant Bacteroidetes, they are accordingly assigned their own phylum....

 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

Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

, and higher plants. While oxygenic phototrophs use water

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 as an electron donor

Electron donor

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....

 for phototrophy, Chloroflexus uses reduced sulfur compounds such as hydrogen sulfide

Hydrogen sulfide

Hydrogen sulfide is the chemical compound with the formula . It is a colorless, very poisonous, flammable gas with the characteristic foul odor of expired eggs perceptible at concentrations as low as 0.00047 parts per million...

, thiosulfate

Thiosulfate

Thiosulfate is an oxyanion of sulfur. The prefix thio indicates that thiosulfate ion is a sulfate ion with one oxygen replaced by a sulfur. Thiosulfate occurs naturally and is produced by certain biochemical processes...

, or elemental sulfur. This belies their antiquated name green non-sulfur bacteria, however Chloroflexus spp. can also utilize hydrogen

Hydrogen

Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

(H₂) as a source of electrons.

Chloroflexus aurantiacus is thought to grow photoheterotroph

Photoheterotroph

Photoheterotrophs are heterotrophic organisms that use light for energy, but cannot use carbon dioxide as their sole carbon source. Consequently, they use organic compounds from the environment to satisfy their carbon requirements. They use compounds such as carbohydrates, fatty acids and...

ically in nature, but it has the capability of fixing inorganic carbon through photoautotrophic growth. Instead of using the Calvin-Benson-Bassham Cycle

Calvin cycle

The Calvin cycle or Calvin–Benson-Bassham cycle or reductive pentose phosphate cycle or C3 cycle or CBB cycle is a series of biochemical redox reactions that take place in the stroma of chloroplasts in photosynthetic organisms...

 typical of plants, Chloroflexus aurantiacus has been demonstrated to use a novel autotrophic pathway known as the 3-Hydroxypropionate pathway

3-Hydroxypropionate pathway

3-Hydroxypropionate Pathway is a CO2 assimilatory pathway observed in bacteria. Inorganic CO2 is fixed by acetyl-CoA and propionyl-CoA carboxylases thus forming malyl-CoA and glyoxylate. Malyl-CoA is further split into acetyl-CoA...

.

The complete electron transport chain

Electron transport chain

An electron transport chain couples electron transfer between an electron donor and an electron acceptor with the transfer of H+ ions across a membrane. The resulting electrochemical proton gradient is used to generate chemical energy in the form of adenosine triphosphate...

 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

Cytochrome c

The Cytochrome complex, or cyt c is a small heme protein found loosely associated with the inner membrane of the mitochondrion. It belongs to the cytochrome c family of proteins. Cytochrome c is a highly soluble protein, unlike other cytochromes, with a solubility of about 100 g/L and is an...

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 events in which non-photosynthetic eukaryote

Eukaryote

A eukaryote is an organism whose cells contain complex structures enclosed within membranes. Eukaryotes may more formally be referred to as the taxon Eukarya or Eukaryota. The defining membrane-bound structure that sets eukaryotic cells apart from prokaryotic cells is the nucleus, or nuclear...

s internalized photosynthetic organisms. The chloroplast

Chloroplast

Chloroplasts are organelles found in plant cells and other eukaryotic organisms that conduct photosynthesis. Chloroplasts capture light energy to conserve free energy in the form of ATP and reduce NADP to NADPH through a complex set of processes called photosynthesis.Chloroplasts are green...

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 type II

Photosystem II

Photosystem II is the first protein complex in the Light-dependent reactions. It is located in the thylakoid membrane of plants, algae, and cyanobacteria. The enzyme uses photons of light to energize electrons that are then transferred through a variety of coenzymes and cofactors to reduce...

 photosynthetic reaction center. One idea is that bacteria with respiratory

Cellular respiration

Cellular respiration is the set of the metabolic reactions and processes that take place in the cells of organisms to convert biochemical energy from nutrients into adenosine triphosphate , and then release waste products. The reactions involved in respiration are catabolic reactions that involve...

 electron transport 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

Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

of photosynthesis.