Epsilonproteobacteria is a class of Proteobacteria

Proteobacteria

The Proteobacteria are a major group of bacteria. They include a wide variety of pathogens, such as Escherichia, Salmonella, Vibrio, Helicobacter, and many other notable genera....

. All 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...

 of this class are, like all Proteobacteria, gram-negative

Gram-negative

Gram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...

.

The Epsilonproteobacteria consist of few known genera, mainly the curved to spirilloid Wolinella spp., Helicobacter

Helicobacter

Helicobacter is a genus of Gram-negative bacteria possessing a characteristic helix shape. They were initially considered to be members of the Campylobacter genus, but since 1989 they have been grouped in their own genus...

spp., and Campylobacter

Campylobacter

Campylobacter is a genus of bacteria that are Gram-negative, spiral, and microaerophilic. Motile, with either unipolar or bipolar flagella, the organisms have a characteristic spiral/corkscrew appearance and are oxidase-positive. Campylobacter jejuni is now recognized as one of the main causes...

spp. Most of the known species inhabit the digestive tract of animals and serve as symbionts

Symbiosis

Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...

 (Wolinella spp. in cows

Cattle

Cattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...

) or pathogen

Pathogen

A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...

s (Helicobacter spp. in the stomach, Campylobacter spp. in the duodenum).

There have also been numerous environmental sequences of Epsilonproteobacteria recovered from hydrothermal vent

Hydrothermal vent

A hydrothermal vent is a fissure in a planet's surface from which geothermally heated water issues. Hydrothermal vents are commonly found near volcanically active places, areas where tectonic plates are moving apart, ocean basins, and hotspots. Hydrothermal vents exist because the earth is both...

s and cold seep

Cold seep

A cold seep is an area of the ocean floor where hydrogen sulfide, methane and other hydrocarbon-rich fluid seepage occurs, often in the form of a brine pool...

 habitats. A member of the class Epsilonproteobacteria occurs as an endosymbiont

Endosymbiont

An endosymbiont is any organism that lives within the body or cells of another organism, i.e. forming an endosymbiosis...

 in the large gill

Gill

A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...

s of the deep water sea snail Alviniconcha hessleri

Alviniconcha hessleri

Alviniconcha hessleri is a species of deep water sea snail, a marine gastropod mollusk in the family Provannidae.These snails are part of the fauna of the hydrothermal vents in Indian Ocean....

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Often the epsilonproteobacteria living in hydrothermal deep sea-vents exhibit chemolithotrophic features, and they are able to meet their energy needs by reducing or oxidixing chemical compounds.