Chlorobium
Encyclopedia
Chlorobium is a genus
of green sulfur bacteria
. They are photolithotrophic oxidizers of sulfur
and most notably utilise a noncyclic electron transport chain to reduce NAD+. Hydrogen sulfide
is used as an electron source and carbon dioxide
its carbon source.
Chlorobium species
exhibit a dark green color; in a Winogradsky column
, the green layer often observed is composed of Chlorobium. This genus lives in strictly anaerobic conditions below the surface of a body of water, commonly the anaerobic
zone of a eutrophic lake.
Chlorobium aggregatum is a species which exists in a symbiotic relationship with a colorless, nonphotosynthetic bacteria. This species looks like a bundle of green bacteria, attached to a central rod-like cell which can move around with a flagellum
. The green, outer bacteria use light to oxidize sulfide
into sulfate
. The inner cell, which is not able to perform photosynthesis
, reduces the sulfate into sulfide. These bacteria divide in unison, giving the structure a multicellular appearance which is highly unusual in bacteria.
Chlorobium species are thought to have played an important part in mass extinction events on Earth. If the oceans turn anoxic (due to the shutdown of ocean circulation) then Chlorobium would be able to out compete other photosynthetic life. They would produce huge quantities of methane
and hydrogen sulfide
which would cause global warming
and acid rain
. This would have huge consequences for other oceanic organisms and also for terrestrial organisms. Evidence for abundant Chlorobium populations is provided by chemical fossils found in sediments deposited at the cretaceous mass extinction.
The complete C. tepidum genome
, which consists of 2.15 megabases (Mb), was sequenced and published in 2002. It synthesizes chlorophyll
a and bacteriochlorophyll
s (BChls) a and c, of which the model organism
has been used to elucidate the biosynthesis of BChl c.
Several of its carotenoid
metabolic pathway
s (including a novel lycopene
cyclase
) have similar counterparts in cyanobacteria.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of 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....
. They are photolithotrophic oxidizers of sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...
and most notably utilise a noncyclic electron transport chain to reduce NAD+. 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...
is used as an electron source and carbon dioxide
Carbon dioxide
Carbon dioxide is a naturally occurring chemical compound composed of two oxygen atoms covalently bonded to a single carbon atom...
its carbon source.
Chlorobium species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
exhibit a dark green color; in a Winogradsky column
Winogradsky column
The Winogradsky column is a simple device for culturing a large diversity of microorganisms. Invented by Sergei Winogradsky, the device is a column of pond mud and water mixed with a carbon source such as newspaper blackened marshmallows or egg-shells and a sulfur source such as gypsum or...
, the green layer often observed is composed of Chlorobium. This genus lives in strictly anaerobic conditions below the surface of a body of water, commonly the anaerobic
Anaerobic organism
An anaerobic organism or anaerobe is any organism that does not require oxygen for growth. It could possibly react negatively and may even die if oxygen is present...
zone of a eutrophic lake.
Chlorobium aggregatum is a species which exists in a symbiotic relationship with a colorless, nonphotosynthetic bacteria. This species looks like a bundle of green bacteria, attached to a central rod-like cell which can move around with a flagellum
Flagellum
A flagellum is a tail-like projection that protrudes from the cell body of certain prokaryotic and eukaryotic cells, and plays the dual role of locomotion and sense organ, being sensitive to chemicals and temperatures outside the cell. There are some notable differences between prokaryotic and...
. The green, outer bacteria use light to oxidize sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...
into sulfate
Sulfate
In inorganic chemistry, a sulfate is a salt of sulfuric acid.-Chemical properties:...
. The inner cell, which is not able to perform photosynthesis
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...
, reduces the sulfate into sulfide. These bacteria divide in unison, giving the structure a multicellular appearance which is highly unusual in bacteria.
Chlorobium species are thought to have played an important part in mass extinction events on Earth. If the oceans turn anoxic (due to the shutdown of ocean circulation) then Chlorobium would be able to out compete other photosynthetic life. They would produce huge quantities of methane
Methane
Methane is a chemical compound with the chemical formula . It is the simplest alkane, the principal component of natural gas, and probably the most abundant organic compound on earth. The relative abundance of methane makes it an attractive fuel...
and 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...
which would cause global warming
Global warming
Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...
and acid rain
Acid rain
Acid rain is a rain or any other form of precipitation that is unusually acidic, meaning that it possesses elevated levels of hydrogen ions . It can have harmful effects on plants, aquatic animals, and infrastructure. Acid rain is caused by emissions of carbon dioxide, sulfur dioxide and nitrogen...
. This would have huge consequences for other oceanic organisms and also for terrestrial organisms. Evidence for abundant Chlorobium populations is provided by chemical fossils found in sediments deposited at the cretaceous mass extinction.
The complete C. tepidum genome
Genome
In modern molecular biology and genetics, the genome is the entirety of an organism's hereditary information. It is encoded either in DNA or, for many types of virus, in RNA. The genome includes both the genes and the non-coding sequences of the DNA/RNA....
, which consists of 2.15 megabases (Mb), was sequenced and published in 2002. It synthesizes 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...
a and 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...
s (BChls) a and c, of which the model organism
Model organism
A model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...
has been used to elucidate the biosynthesis of BChl c.
Several of its 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...
metabolic pathway
Metabolic pathway
In biochemistry, metabolic pathways are series of chemical reactions occurring within a cell. In each pathway, a principal chemical is modified by a series of chemical reactions. Enzymes catalyze these reactions, and often require dietary minerals, vitamins, and other cofactors in order to function...
s (including a novel lycopene
Lycopene
Lycopene is a bright red carotene and carotenoid pigment and phytochemical found in tomatoes and other red fruits and vegetables, such as red carrots, watermelons and papayas...
cyclase
Cyclase
A cyclase is an enzyme, almost always a lyase, that catalyzes a chemical reaction to form a cyclic compound. Important cyclase enzymes include:* Adenylyl cyclase, which forms cyclic AMP from adenosine triphosphate...
) have similar counterparts in cyanobacteria.