The green sulfur bacteria are a family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 of obligately 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...

 photoautotrophic bacteria

Bacteria

Bacteria are a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria have a wide range of shapes, ranging from spheres to rods and spirals...

. Most closely related to the distant Bacteroidetes

Bacteroidetes

The phylum Bacteroidetes is composed of three large classes of bacteria that are widely distributed in the environment, including in soil, in sediments, sea water and in the guts and on the skin of animals....

, they are accordingly assigned their own phylum

Phylum

In biology, a phylum The term was coined by Georges Cuvier from Greek φῦλον phylon, "race, stock," related to φυλή phyle, "tribe, clan." is a taxonomic rank below kingdom and above class. "Phylum" is equivalent to the botanical term division....

.

Green sulfur bacteria are non-motile (except Chloroherpeton thalassium, which may glide

Bacterial gliding

Bacterial gliding is a process whereby a bacterium can move under its own power. This process does not involve the use of flagella, which is a more common means of motility in bacteria...

) and come in spheres, rods, and spirals. 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...

 is achieved using 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...

 (BChl) c, d, or e, in addition to BChl a and chlorophyll a

Chlorophyll a

Chlorophyll a is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light. This photosynthetic pigment is essential for photosynthesis in eukaryotes, cyanobacteria and prochlorophytes because of its role as primary...

, in 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 attached to the membrane. They use 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 :...

 ions, 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...

 or ferrous iron 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....

 and the process is mediated by the type I reaction centre and Fenna-Matthews-Olson complex

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...

. Elemental 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...

 deposited outside the cell may be further oxidized. By contrast, the photosynthesis in plants uses water as electron donor and produces oxygen.

Chlorobium

Chlorobium

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+...

 tepidum has emerged as a 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...

 for the group, and although only ten 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....

s have been sequenced, these are quite comprehensive of the family's biodiversity. Their 2-3 Mb genomes encode

Genetic code

The genetic code is the set of rules by which information encoded in genetic material is translated into proteins by living cells....

 1750-2800 gene

Gene

A gene is a molecular unit of heredity of a living organism. It is a name given to some stretches of DNA and RNA that code for a type of protein or for an RNA chain that has a function in the organism. Living beings depend on genes, as they specify all proteins and functional RNA chains...

s, 1400-1500 of which are common to all strains. The apparent absence of two-component histidine

Histidine

Histidine Histidine, an essential amino acid, has a positively charged imidazole functional group. It is one of the 22 proteinogenic amino acids. Its codons are CAU and CAC. Histidine was first isolated by German physician Albrecht Kossel in 1896. Histidine is an essential amino acid in humans...

-kinase

Kinase

In chemistry and biochemistry, a kinase is a type of enzyme that transfers phosphate groups from high-energy donor molecules, such as ATP, to specific substrates, a process referred to as phosphorylation. Kinases are part of the larger family of phosphotransferases...

s and response regulators suggest limited phenotypic plasticity

Phenotypic plasticity

Phenotypic plasticity is the ability of an organism to change its phenotype in response to changes in the environment. Such plasticity in some cases expresses as several highly morphologically distinct results; in other cases, a continuous norm of reaction describes the functional interrelationship...

. Their small dependence on organic molecule transporters and transcription factor

Transcription factor

In molecular biology and genetics, a transcription factor is a protein that binds to specific DNA sequences, thereby controlling the flow of genetic information from DNA to mRNA...

s also indicate that these organisms are adapted to a narrow range of energy-limited conditions, an ecology

Ecology

Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...

 shared with the simpler cyanobacteria, Prochlorococcus

Prochlorococcus

Prochlorococcus is a genus of very small marine cyanobacteria with an unusual pigmentation . These bacteria belong to the photosynthetic picoplankton and are probably the most abundant photosynthetic organism on Earth....

and Synechococcus

Synechococcus

Synechococcus is a unicellular cyanobacterium that is very widespread in the marine environment. Its size varies from 0.8 µm to 1.5 µm...

A species of green sulfur bacteria has been found living near a black smoker off the coast of Mexico

Mexico

The United Mexican States , commonly known as Mexico , is a federal constitutional republic in North America. It is bordered on the north by the United States; on the south and west by the Pacific Ocean; on the southeast by Guatemala, Belize, and the Caribbean Sea; and on the east by the Gulf of...

 at a depth of 2,500 meters beneath the surface of the Pacific Ocean

Pacific Ocean

The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...

. At this depth, the bacterium, designated GSB1, lives off the dim glow of the thermal vent since no sunlight can penetrate to that depth.

Green sulfur bacteria appear in Lake Matano

Lake Matano

Lake Matano , also known as Matana, is a natural lake in South Sulawesi, Indonesia. It is the deepest lake in Indonesia , and the 10th deepest lake in the world. It is located at .- Endemic Fish of Matano :...

, Indonesia, at a depth of approximately 110–120 meters. The population may include the species, Chlorobium ferrooxidans.

Phylogeny

The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LSPN)

and the phylogeny is based on 16S rRNA-based LTP release 106 by The All-Species Living Tree Project 
Notes:

♪ Prokaryotes where no pure (axenic) cultures are isolated or available, i. e. not cultivated or can not be sustained in culture for more than a few serial passages

♥ Strains not lodged at National Center for Biotechnology Information

National Center for Biotechnology Information

The National Center for Biotechnology Information is part of the United States National Library of Medicine , a branch of the National Institutes of Health. The NCBI is located in Bethesda, Maryland and was founded in 1988 through legislation sponsored by Senator Claude Pepper...

 (NCBI) or listed in the List of Prokaryotic names with Standing in Nomenclature (LPSN)

♠ Strains found at the National Center for Biotechnology Information

National Center for Biotechnology Information

The National Center for Biotechnology Information is part of the United States National Library of Medicine , a branch of the National Institutes of Health. The NCBI is located in Bethesda, Maryland and was founded in 1988 through legislation sponsored by Senator Claude Pepper...

 (NCBI) but not listed in the List of Prokaryotic names with Standing in Nomenclature (LSPN)