Chlorosome
Encyclopedia
A Chlorosome is a photosynthetic antenna complex
found in green sulfur bacteria
(GSB) and some green filamentous anoxygenic phototrophs (FAP) (Chloroflexaceae, Oscillochloridaceae). They differ from other antenna complexes by their large size and lack of protein
matrix supporting the photosynthetic pigments. Green sulfur bacteria
are a group of organisms that generally live in extremely low-light environments, such as at depths of 100 meters in the Black Sea
. The ability to capture light energy and rapidly deliver it to where it needs to go is essential to these bacteria, some of which see only a few photons of light per chlorophyll
per day. To achieve this, the bacteria contain chlorosome structures, which contain up to 250,000 chlorophyll
molecules. Chlorosomes are ellipsoidal bodies, in GSB their length varies from 100 to 200 nm, width of 50-100 nm and height of 15 - 30 nm , in FAP the chlorosomes are somewhat smaller.
via FMO-proteins
and a chlorosome baseplate composed of csmA proteins. Chlorosomes from FAP lack the FMO complex. The composition of the chlorosomes is mostly bacteriochlorophyll
with small amounts of carotenoid
s and quinone
s surrounded by a galactolipid
monolayer with ten different proteins attached to it.
and carotenoid
s are two molecules responsible for harvesting light energy. Current models of the organization of bacteriochlorophyll
and carotenoid
s (the main constituents) inside the chlorosomes have put them in a lamellar organization, where the long farnesol
tails of the bacteriochlorophyll intermix with carotenoids and each other, forming a structure resembling a lipid multilayer .
Recently, another study has determined the organization of the bacteriochlorophyll
molecules in green sulfur bacteria
. Because they have been so difficult to study, the chlorosomes in green sulfur bacteria
are the last class of light-harvesting complex
es to be characterized structurally by scientists. Each individual chlorosome has a unique organization and this variability in composition had prevented scientists from using X-ray crystallography
to characterize the internal structure. To get around this problem, the team used a combination of different experimental approaches. Genetic techniques to create a mutant
bacterium with a more regular internal structure, cryo-electron microscopy
to identify the larger distance constraints for the chlorosome, solid-state nuclear magnetic resonance
(NMR) spectroscopy to determine the structure of the chlorosome's component chlorophyll
molecules, and modeling
to bring together all of the pieces and create a final picture of the chlorosome.
To create the mutant, three genes were inactivated that green sulfur bacteria
acquired late in their evolution
. In this way it was possible to go backward in evolutionary time to an intermediate state with much less variable and better ordered chlorosome organelles than the wild-type. The chlorosomes were isolated from the mutant
and the wild-type forms of the bacteria. Cryo-electron microscopy
was used to take pictures of the chlorosomes. The images reveal that the chlorophyll
molecules inside chlorosomes have a nanotube
shape. The team then used MAS NMR spectroscopy
to resolve the microscopic arrangement of chlorophyll
inside the chlorosome. With distance constraints and DFT
ring current analyses the organization was found to consist of unique syn-anti monomer stacking. The combination of NMR
, cryo-electron microscopy
and modeling
enabled the scientists to determine that the chlorophyll
molecules in green sulfur bacteria
are arranged in helices. In the mutant
bacteria, the chlorophyll
molecules are positioned at a nearly 90-degree angle in relation to the long axis of the nanotubes, whereas the angle is less steep in the wild-type organism. The structural framework can accommodate disorder to improve the biological light harvesting function, which implies that a less ordered structure has a better performance.
or biofuel
.
Antenna complex
The light-harvesting complex of plants is an array of protein and chlorophyll molecules embedded in the thylakoid membrane which transfer light energy to one chlorophyll a molecule at the reaction center of a photosystem....
found in 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....
(GSB) and some green filamentous anoxygenic phototrophs (FAP) (Chloroflexaceae, Oscillochloridaceae). They differ from other antenna complexes by their large size and lack of protein
Protein
Proteins are biochemical compounds consisting of one or more polypeptides typically folded into a globular or fibrous form, facilitating a biological function. A polypeptide is a single linear polymer chain of amino acids bonded together by peptide bonds between the carboxyl and amino groups of...
matrix supporting the photosynthetic pigments. 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....
are a group of organisms that generally live in extremely low-light environments, such as at depths of 100 meters in the Black Sea
Black Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...
. The ability to capture light energy and rapidly deliver it to where it needs to go is essential to these bacteria, some of which see only a few photons of light per chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
per day. To achieve this, the bacteria contain chlorosome structures, which contain up to 250,000 chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
molecules. Chlorosomes are ellipsoidal bodies, in GSB their length varies from 100 to 200 nm, width of 50-100 nm and height of 15 - 30 nm , in FAP the chlorosomes are somewhat smaller.
Structure
Inside the GSB cell, the chlorosomes are thought to be attached to the reaction centers in the cell membraneCell membrane
The cell membrane or plasma membrane is a biological membrane that separates the interior of all cells from the outside environment. The cell membrane is selectively permeable to ions and organic molecules and controls the movement of substances in and out of cells. It basically protects the cell...
via FMO-proteins
Fenna-Matthews-Olson complex
The Fenna-Matthews-Olson complex is a water soluble complex and was the first pigment-protein complex that has been structure analyzed by x-ray spectroscopy. It appears in green sulfur bacteria and mediates the excitation energy transfer from the light-harvesting chlorosomes to the membrane...
and a chlorosome baseplate composed of csmA proteins. Chlorosomes from FAP lack the FMO complex. The composition of the chlorosomes is mostly 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...
with small amounts of carotenoid
Carotenoid
Carotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...
s and quinone
Quinone
A quinone is a class of organic compounds that are formally "derived from aromatic compounds [such as benzene or naphthalene] by conversion of an even number of –CH= groups into –C– groups with any necessary rearrangement of double bonds," resulting in "a fully conjugated cyclic dione structure."...
s surrounded by a galactolipid
Lipid
Lipids constitute a broad group of naturally occurring molecules that include fats, waxes, sterols, fat-soluble vitamins , monoglycerides, diglycerides, triglycerides, phospholipids, and others...
monolayer with ten different proteins attached to it.
Organization of the light harvesting pigments
BacteriochlorophyllBacteriochlorophyll
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...
and carotenoid
Carotenoid
Carotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...
s are two molecules responsible for harvesting light energy. Current models of the organization of 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...
and carotenoid
Carotenoid
Carotenoids are tetraterpenoid organic pigments that are naturally occurring in the chloroplasts and chromoplasts of plants and some other photosynthetic organisms like algae, some bacteria, and some types of fungus. Carotenoids can be synthesized fats and other basic organic metabolic building...
s (the main constituents) inside the chlorosomes have put them in a lamellar organization, where the long farnesol
Farnesol
Farnesol is a natural organic compound which is an acyclic sesquiterpene alcohol found as a colorless liquid. It is insoluble in water, but miscible with oils...
tails of the bacteriochlorophyll intermix with carotenoids and each other, forming a structure resembling a lipid multilayer .
Recently, another study has determined the organization of the 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...
molecules in 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....
. Because they have been so difficult to study, the chlorosomes in 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....
are the last class of light-harvesting complex
Light-harvesting complex
A light-harvesting complex is a complex of subunit proteins that may be part of a larger supercomplex of a photosystem, the functional unit in photosynthesis. It is used by plants and photosynthetic bacteria to collect more of the incoming light than would be captured by the photosynthetic reaction...
es to be characterized structurally by scientists. Each individual chlorosome has a unique organization and this variability in composition had prevented scientists from using X-ray crystallography
X-ray crystallography
X-ray crystallography is a method of determining the arrangement of atoms within a crystal, in which a beam of X-rays strikes a crystal and causes the beam of light to spread into many specific directions. From the angles and intensities of these diffracted beams, a crystallographer can produce a...
to characterize the internal structure. To get around this problem, the team used a combination of different experimental approaches. Genetic techniques to create a mutant
Mutant
In biology and especially genetics, a mutant is an individual, organism, or new genetic character, arising or resulting from an instance of mutation, which is a base-pair sequence change within the DNA of a gene or chromosome of an organism resulting in the creation of a new character or trait not...
bacterium with a more regular internal structure, cryo-electron microscopy
Cryo-electron microscopy
Cryo-electron microscopy , or electron cryomicroscopy, is a form of transmission electron microscopy where the sample is studied at cryogenic temperatures...
to identify the larger distance constraints for the chlorosome, solid-state nuclear magnetic resonance
Solid-state nuclear magnetic resonance
Solid-state NMR spectroscopy is a kind of nuclear magnetic resonance spectroscopy, characterized by the presence of anisotropic interactions.-Introduction:Basic concepts...
(NMR) spectroscopy to determine the structure of the chlorosome's component chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
molecules, and modeling
Molecular modelling
Molecular modelling encompasses all theoretical methods and computational techniques used to model or mimic the behaviour of molecules. The techniques are used in the fields of computational chemistry, computational biology and materials science for studying molecular systems ranging from small...
to bring together all of the pieces and create a final picture of the chlorosome.
To create the mutant, three genes were inactivated that 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....
acquired late in their 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...
. In this way it was possible to go backward in evolutionary time to an intermediate state with much less variable and better ordered chlorosome organelles than the wild-type. The chlorosomes were isolated from the mutant
Mutant
In biology and especially genetics, a mutant is an individual, organism, or new genetic character, arising or resulting from an instance of mutation, which is a base-pair sequence change within the DNA of a gene or chromosome of an organism resulting in the creation of a new character or trait not...
and the wild-type forms of the bacteria. Cryo-electron microscopy
Cryo-electron microscopy
Cryo-electron microscopy , or electron cryomicroscopy, is a form of transmission electron microscopy where the sample is studied at cryogenic temperatures...
was used to take pictures of the chlorosomes. The images reveal that the chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
molecules inside chlorosomes have a nanotube
Carbon nanotube
Carbon nanotubes are allotropes of carbon with a cylindrical nanostructure. Nanotubes have been constructed with length-to-diameter ratio of up to 132,000,000:1, significantly larger than for any other material...
shape. The team then used MAS NMR spectroscopy
NMR spectroscopy
Nuclear magnetic resonance spectroscopy, most commonly known as NMR spectroscopy, is a research technique that exploits the magnetic properties of certain atomic nuclei to determine physical and chemical properties of atoms or the molecules in which they are contained...
to resolve the microscopic arrangement of chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
inside the chlorosome. With distance constraints and DFT
DFT
DFT may stand for:*Discrete Fourier transform*Decision field theory*Density functional theory*Demand Flow Technology*The United Kingdom's Department for Transport*Design For Test*Deareating Feed Tank*Digital Film Technology maker of the Spirit DataCine...
ring current analyses the organization was found to consist of unique syn-anti monomer stacking. The combination of NMR
NMR
NMR may refer to:Applications of Nuclear Magnetic Resonance:* Nuclear magnetic resonance* NMR spectroscopy* Solid-state nuclear magnetic resonance* Protein nuclear magnetic resonance spectroscopy* Proton NMR* Carbon-13 NMR...
, cryo-electron microscopy
Cryo-electron microscopy
Cryo-electron microscopy , or electron cryomicroscopy, is a form of transmission electron microscopy where the sample is studied at cryogenic temperatures...
and modeling
Molecular modelling
Molecular modelling encompasses all theoretical methods and computational techniques used to model or mimic the behaviour of molecules. The techniques are used in the fields of computational chemistry, computational biology and materials science for studying molecular systems ranging from small...
enabled the scientists to determine that the chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
molecules in 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....
are arranged in helices. In the mutant
Mutant
In biology and especially genetics, a mutant is an individual, organism, or new genetic character, arising or resulting from an instance of mutation, which is a base-pair sequence change within the DNA of a gene or chromosome of an organism resulting in the creation of a new character or trait not...
bacteria, the chlorophyll
Chlorophyll
Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...
molecules are positioned at a nearly 90-degree angle in relation to the long axis of the nanotubes, whereas the angle is less steep in the wild-type organism. The structural framework can accommodate disorder to improve the biological light harvesting function, which implies that a less ordered structure has a better performance.
An alternative energy source
The interactions that lead to the assembly of the chlorophylls in chlorosomes are rather simple and the results may one day be used to build artificial photosynthetic systems that convert solar energy to electricityElectricity
Electricity is a general term encompassing a variety of phenomena resulting from the presence and flow of electric charge. These include many easily recognizable phenomena, such as lightning, static electricity, and the flow of electrical current in an electrical wire...
or biofuel
Biofuel
Biofuel is a type of fuel whose energy is derived from biological carbon fixation. Biofuels include fuels derived from biomass conversion, as well as solid biomass, liquid fuels and various biogases...
.
List of bacterial species containing chlorosomes
- Chlorobiaceae
- Chlorobium limicola
- Chlorobium phaeobacteroides
- Chlorobium phaeovibrioides
- Chlorobium vibrioforme
- Chlorobium tepidum
- Pelodictyon lutoleum
- Prostecochloris aestuarii
- Chloroflexaceae
- Chloroflexus aurantiacusChloroflexus aurantiacusChloroflexus aurantiacus is a photosynthetic bacterium isolated from hot springs, belonging to the green non-sulfur bacteria. This organism is 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...
- Chloroflexus aggregans
- Chloronema giganteum
- Chloroflexus aurantiacus
- Oscillochloridaceae
- Oscillochloris trichoides
- AcidobacteriaceaeAcidobacteriaAcidobacteria are a newly devised phylum of Bacteria, whose members are physiologically diverse and ubiquitous, especially in soils, but are under-represented in culture....
- Chloracidobacterium thermophilum