''Aquifex pyrophilus'' is a

gram-negative Gram-negative bacteria are bacteria that do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. They are characterized by their cell envelopes, which are composed of a thin peptidoglycan cell wall ...

, non-spore forming,

rod-shaped A bacillus (), also called a bacilliform bacterium or often just a rod (when the context makes the sense clear), is a rod-shaped bacterium or archaeon. Bacilli are found in many different taxonomic groups of bacteria. However, the name '' Baci ...

bacteria Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...

. It is one of a handful of species in the

Aquificota The ''Aquificota'' phylum is a diverse collection of bacteria that live in harsh environmental settings. The name ''Aquificota'' was given to this phylum based on an early genus identified within this group, '' Aquifex'' (“water maker”), whic ...

phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...

, which are a group of

thermophilic A thermophile is an organism—a type of extremophile—that thrives at relatively high temperatures, between . Many thermophiles are archaea, though they can be bacteria or fungi. Thermophilic eubacteria are suggested to have been among the earl ...

bacteria that are found near underwater volcanoes or

hot spring A hot spring, hydrothermal spring, or geothermal spring is a spring produced by the emergence of geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow bodies of magma (molten rock) or by circ ...

Name Meaning

''Aquifex pyrophilus'' has a name that references its

respiration Respiration may refer to: Biology * Cellular respiration, the process in which nutrients are converted into useful energy in a cell ** Anaerobic respiration, cellular respiration without oxygen ** Maintenance respiration, the amount of cellul ...

and its

habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...

. The name "Aquifex" means "water-maker" in

Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...

. The name was assigned to ''A. pyrophilus'' because it typically uses

oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...

as its

and

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...

as a byproduct. The name "Pyrophilus" can be broken down into "Pyro" and "Philus". "Pyro" is Latin for fire, heat, or high temperature and "Philus" is a Latin word for "loving". Therefore the term "pyrophilus" can be interpreted as "heat loving" which refers to the

''A. pyrophilus'' is typically found in.

Habitat

The genus Aquifex is a contains some of the most thermophilic bacterium of all known bacteria. ''A. pyrophilus'' is an aquatic microbe that is typically found near underwater volcanoes, marine hydrothermal vents, and/or

s where temperatures are extremely high and pressure can be immense. ''A. pyrophilus'' has shown resistance to

ultraviolet light Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nm (with a corresponding frequency around 30 PHz) to 400 nm (750 THz), shorter than that of visible light, but longer than X-rays. UV radiation i ...

and

ionizing radiation Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...

. The ''Aquifex''

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...

is rather intolerable to

therefore it is only found in low-oxygenated environments. Despite this, ''Aquifex'' remains one of only

aerobic Aerobic means "requiring air," in which "air" usually means oxygen. Aerobic may also refer to * Aerobic exercise, prolonged exercise of moderate intensity * Aerobics, a form of aerobic exercise * Aerobic respiration, the aerobic process of cel ...

bacterial

hyperthermophile A hyperthermophile is an organism that thrives in extremely hot environments—from 60 °C (140 °F) upwards. An optimal temperature for the existence of hyperthermophiles is often above 80 °C (176 °F). Hyperthermophiles are often within the doma ...

s known. Oxygen is limited near these hydrothermal vents and underwater volcanos because of the extremely high temperature and reducing power of volcanic gases like H₂S. ''A. pyrophilus'' thrives where the oxic and

anoxic The term anoxia means a total depletion in the level of oxygen, an extreme form of hypoxia or "low oxygen". The terms anoxia and hypoxia are used in various contexts: * Anoxic waters, sea water, fresh water or groundwater that are depleted of diss ...

zones meet in these environments because of the high availability of hydrogen and

thiosulfate Thiosulfate ( IUPAC-recommended spelling; sometimes thiosulphate in British English) is an oxyanion of sulfur with the chemical formula . Thiosulfate also refers to the compounds containing this anion, which are the salts of thiosulfuric acid, ...

. ''Aquifex pyrophilus'' was discovered at

Kolbeinsey Ridge The Kolbeinsey Ridge is a segment of the Mid-Atlantic Ridge located to the north of Iceland in the Arctic Ocean. It is bounded to the south by the Tjörnes Fracture Zone, which connects the submarine ridge to the on-shore Northern Volcanic Zone ri ...

, North of

Iceland Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...

Robert Huber Robert Huber (; born 20 February 1937) is a German biochemist and Nobel laureate. known for his work crystallizing an intramembrane protein important in photosynthesis and subsequently applying X-ray crystallography to elucidate the protein's st ...

and

Karl Stetter Karl Otto Stetter (born 16 July 1941) is a German microbiologist and authority on astrobiology. He is an expert on microbial life at high temperatures. Career Stetter was born in Munich and studied biology at the Technical University of Munich ...

in 1992. In Huber's and Stetter's first analysis of the bacteria, they found that ''A. pyrophilus'' had an optimum pH of 6.8 but ranged anywhere between 5.4 and 7.5, grew at temperatures ranging from 67°C to 95°C with an optimum at 85°C, and had optimal growth with a

NaCl Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g/ ...

concentration of 3% (range of 1-5%). ''A. pyrophilus'' is 2 to 6 micrometers long and has a diameter of around half a micrometer. It has eight polytrichously inserted flagella making it motile. ''A. pyrophilus'' can grow singly, in pairs, and/or form large cell conglomerations, comprising up to 100 individual cells.

Metabolism

''A. pyrophilus'' is strictly

chemolithoautotrophic A lithoautotroph is an organism which derives energy from reactions of reduced compounds of mineral (inorganic) origin. Two types of lithoautotrophs are distinguished by their energy source; photolithoautotrophs derive their energy from light while ...

. It is capable of using

in its

, but can also grow anaerobically by nitrate reduction. In

conditions, ''A. pyrophilus'' oxidizes molecular hydrogen and yields H₂O and ATP. Other electron donors that A. pyrophilus uses in aerobic conditions are S° and S₂O₃^2-. Byproducts include

sulfuric acid Sulfuric acid (American spelling and the preferred IUPAC name) or sulphuric acid ( Commonwealth spelling), known in antiquity as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen, with the molecular formu ...

from S° and S₂O₃^2- and

hydrogen sulfide Hydrogen sulfide is a chemical compound with the formula . It is a colorless chalcogen-hydride gas, and is poisonous, corrosive, and flammable, with trace amounts in ambient atmosphere having a characteristic foul odor of rotten eggs. The unde ...

from S° and H₂.

Lineage and Phylogeny

''A. pyrophilus'' has a relatively small

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ge ...

. Out of the known thermophile genomes, ''A. pyrophilus'' is the smallest. Due to its small genome, its ability to survive in extreme heat, its ability to be resistant toward

and

, and because of

phylogenetic In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups o ...

analyses of the small-subunit 16S

rRNA Ribosomal ribonucleic acid (rRNA) is a type of non-coding RNA which is the primary component of ribosomes, essential to all cells. rRNA is a ribozyme which carries out protein synthesis in ribosomes. Ribosomal RNA is transcribed from ribosoma ...

gene, ''A. pyrophilus'' is thought to be one of the oldest species in the bacteria domain. Investigations of the

position of

Aquificales The ''Aquificota'' phylum (biology), phylum is a diverse collection of bacteria that live in harsh environmental settings. The name ''Aquificota'' was given to this phylum based on an early genus identified within this group, ''Aquifex'' (“wate ...

have utilized the

concatenated In formal language theory and computer programming, string concatenation is the operation of joining character strings end-to-end. For example, the concatenation of "snow" and "ball" is "snowball". In certain formalisations of concatenat ...

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...

s shared within the Aquificales order and ''A. pyrophilus''. The results show that the Aquificales are most closely related to

Thermotogales The Thermotogota are a phylum of the domain (biology), domain Bacteria. The phylum Thermotogota is composed of Gram-negative staining, anaerobic organism, anaerobic, and mostly thermophilic and hyperthermophilic bacteria.Gupta, RS (2014) The Phyl ...

when observing whole-genome information. Additionally, Aquificales were found to be somewhat closely related to ε-proteobacteria in

phylogenetic tree A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...

s. This slight ambiguity in the placement of Aquificales on the phylogenetic tree leaves room for some more research in this field. Despite this, there is overwhelming evidence that Aquificales, including ''A. pyrophilus'', are some of the earliest bacteria to branch from archaea.This has led to hypothesis that these bacteria evolved when the

earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...

was still hot and had a thin

atmosphere An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...

References

External links

Type strain of ''Aquifex pyrophilus'' at Bac''Dive'' - the Bacterial Diversity Metadatabase
{{Taxonbar, from=Q4782892 Aquificota Bacteria described in 1992