''Aquifex'' is a bacterial

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

, belonging to

phylum In biology, a phylum (; : phyla) is a level of classification, or taxonomic rank, that is below Kingdom (biology), kingdom and above Class (biology), class. Traditionally, in botany the term division (taxonomy), division has been used instead ...

Aquificota 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 ...

. There is one species of ''Aquifex'' with a validly published name – '' A. pyrophilus'' – but "'' A. aeolicus''" is sometimes considered as species though it has no standing as a name given it has not been validly or effectively published. ''Aquifex'' spp. are extreme thermophiles, growing best at temperature of 85 °C to 95 °C. They are members of the ''

Bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...

'' as opposed to the other inhabitants of extreme environments, the

Archaea Archaea ( ) is a Domain (biology), domain of organisms. Traditionally, Archaea only included its Prokaryote, prokaryotic members, but this has since been found to be paraphyletic, as eukaryotes are known to have evolved from archaea. Even thou ...

. ''Aquifex'' spp. are rod-shaped bacteria with a length of 2 to 6 μm, have a diameter of around 0.5 μm and are motile. They are non-

spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...

forming,

Gram negative Gram-negative bacteria are bacteria that, unlike gram-positive bacteria, do not retain the crystal violet stain used in the Gram staining method of bacterial differentiation. Their defining characteristic is that their cell envelope consists of ...

autotrophs An autotroph is an organism that can convert abiotic sources of energy into energy stored in organic compounds, which can be used by other organisms. Autotrophs produce complex organic compounds (such as carbohydrates, fats, and proteins) us ...

. ''Aquifex'' means ''water-maker'' in Latin, and refers to the fact that its method of respiration creates water. ''Aquifex'' tend to form cell aggregates composed of up to 100 individual cells. ''Aquifex'' spp. are thermophilic and often grow near underwater

volcano A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most oft ...

es or

hot spring A hot spring, hydrothermal spring, or geothermal spring is a Spring (hydrology), spring produced by the emergence of Geothermal activity, geothermally heated groundwater onto the surface of the Earth. The groundwater is heated either by shallow ...

s. ''A. aeolicus'' requires

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

to survive, but can grow in levels of oxygen as low as 7.5 ppm. '' A. pyrophilus'' can even grow anaerobically by reducing

nitrogen Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...

instead of oxygen. Like other thermophilic bacteria, ''Aquifex'' has important uses in industrial processes. The

genome 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 genes, other functional regions of the genome such as ...

of "''A. aeolicus''" has been completed.^, This was made easier by the fact that the length of the genome is only about a third of the length of the genome for '' E. coli''. Comparison of the ''A. aeolicus'' genome to other organisms showed that around 16% of its genes originated from the

domain. Members of this genus are thought to be some of the earliest members of the eubacteria domain. "''A. aeolicus''" was discovered north of

Sicily Sicily (Italian language, Italian and ), officially the Sicilian Region (), is an island in the central Mediterranean Sea, south of the Italian Peninsula in continental Europe and is one of the 20 regions of Italy, regions of Italy. With 4. ...

, while ''A. pyrophilus'' was first found just north of

Iceland Iceland is a Nordic countries, Nordic island country between the Atlantic Ocean, North Atlantic and Arctic Oceans, on the Mid-Atlantic Ridge between North America and Europe. It is culturally and politically linked with Europe and is the regi ...

Genome structure

The complete genome for ''A. aeolicus'' consists of 1,551,335 base pairs with over 1500

open reading frame In molecular biology, reading frames are defined as spans of DNA sequence between the start and stop codons. Usually, this is considered within a studied region of a prokaryotic DNA sequence, where only one of the six possible reading frames ...

s (ORFs) or chromosomal coding sequences. An extremely large portion (over 90%) of the genome are protein-coding regions and there are no significant non-coding repeats. Though the ''A. aeolicus'' genome is dense, many enzyme subunits used for respiration processes are found in separate

operon In genetics, an operon is a functioning unit of DNA containing a cluster of genes under the control of a single promoter. The genes are transcribed together into an mRNA strand and either translated together in the cytoplasm, or undergo splic ...

s. Any repairs to the genome are done by a protein like DNA polymerase beta found in most eukaryotes.

Cell metabolism

''Aquifex'' respiration and fixation pathways use similar pathways to that of other

autotroph An autotroph is an organism that can convert Abiotic component, abiotic sources of energy into energy stored in organic compounds, which can be used by Heterotroph, other organisms. Autotrophs produce complex organic compounds (such as carbohy ...

ic bacteria. Carbon fixation is done using the reductive TCA cycle and forms acetyl-CoA as well as many other bio-synthetic materials. Many bacteria use products from the TCA cycle in the pentose-phosphate pathway and Entner-Doudoroff pathway or Embden-Meyerhof-Parnas pathway; however, many enzymes that are necessary for these gluconeogenic processes have not been identified in ''A. aeolicus,'' suggesting a different pathway might be used. ''A. aeolicus'' needs oxygen at concentrations higher than 7.5 ppm to perform respiration while ''A. pyrophilus'' is capable of respiration with nitrogen. However, both species have a nitrate reductase and nitrate transporter genes located within their genome. The enzymes used in other bacteria for oxygen respiration are used by ''Aquifex''. Many other

oxidoreductase In biochemistry, an oxidoreductase is an enzyme that catalyzes the transfer of electrons from one molecule, the reductant, also called the electron donor, to another, the oxidant, also called the electron acceptor. This group of enzymes usually ut ...

s are present; however, their physiological role is unknown. ''Aquifex'' oxides thiosulfate, molecular hydrogen, and sulfur within their respiratory pathway.

Phylogeny

Phylogenetic trees that are based on small subunit rRNA suggest that ''Aquificales'' are some of the earliest bacteria that branched from Archaea. However, phylogenetic trees based on protein contradict this argument. The exact phylogeny is hard to determine because of this and the many

horizontal gene transfer Horizontal gene transfer (HGT) or lateral gene transfer (LGT) is the movement of genetic material between organisms other than by the ("vertical") transmission of DNA from parent to offspring (reproduction). HGT is an important factor in the e ...

s within the lineage. These factors lead many to believe the phylum of ''Aquifex'' is basal next to '' Thermotogota'', another hyperthermophilic phylum, or are a part of the Campylobacterota, a highly diverse group of hydrothermal dwelling species.

Research potential

''A. aeolicus'' is used as a model organism for hyperthermophilic bacterium. Many studies have looked at the ''Aquifex''

hydrogenase A hydrogenase is an enzyme that Catalysis, catalyses the reversible Redox, oxidation of molecular hydrogen (H2), as shown below: Hydrogen oxidation () is coupled to the reduction of electron acceptors such as oxygen, nitrate, Ferric, ferric i ...

s ability to perform the reversible oxidation of dihydrogen ( the oxidation reaction) at extremely high temperatures. The success of the properties within the hydrogenases of ''Aquifex'' mark the genus as a possible renewable bio-catalysts for hydrogen based fuel cells.

References

External links