''Aquifex'' is a

bacterial 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 ...

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 ...

, belonging to

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 ...

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 ...

. 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 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 ...

, growing best at temperature of 85 °C to 95 °C. They are members of the ''

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 ...

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

Archaea Archaea ( ; singular archaeon ) is a domain of single-celled organisms. These microorganisms lack cell nuclei and are therefore prokaryotes. Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebac ...

. ''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 or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

forming,

Gram negative The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram. Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to th ...

autotrophs An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Works", ...

. ''Aquifex'' means ''water-maker'' in Latin, and refers to the fact that its method of

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 ...

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 a rupture 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 often found where tectonic plates are ...

es 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 ...

s. ''A. aeolicus'' requires

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 ...

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

anaerobic Anaerobic means "living, active, occurring, or existing in the absence of free oxygen", as opposed to aerobic which means "living, active, or occurring only in the presence of oxygen." Anaerobic may also refer to: * Anaerobic adhesive, a bonding a ...

ally by reducing

nitrogen Nitrogen is the chemical element with the symbol N and atomic number 7. Nitrogen is a nonmetal and the lightest member of group 15 of the periodic table, often called the pnictogens. It is a common element in the universe, estimated at se ...

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

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 ...

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 ''Escherichia coli'' (),Wells, J. C. (2000) Longman Pronunciation Dictionary. Harlow ngland Pearson Education Ltd. also known as ''E. coli'' (), is a Gram-negative, facultative anaerobic, rod-shaped, coliform bacterium of the genus ''Escher ...

''. 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 (man) it, Siciliana (woman) , population_note = , population_blank1_title = , population_blank1 = , demographics_type1 = Ethnicity , demographics1_footnotes = , demographi ...

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

Genome structure

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

open reading frame In molecular biology, open reading frames (ORFs) 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 readin ...

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 DNA polymerase beta, also known as POLB, is an enzyme present in eukaryotes. In humans, it is encoded by the ''POLB'' gene. Function In eukaryotic cells, DNA polymerase beta (POLB) performs base excision repair (BER) required for DNA mainten ...

found in most eukaryotes.

Cell metabolism

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

autotroph An autotroph or primary producer is an organism that produces complex organic compounds (such as carbohydrates, fats, and proteins) using carbon from simple substances such as carbon dioxide,Morris, J. et al. (2019). "Biology: How Life Works", ...

ic bacteria. Carbon fixation is done using the

reductive TCA cycle Reduction, reduced, or reduce may refer to: Science and technology Chemistry * Reduction (chemistry), part of a reduction-oxidation (redox) reaction in which atoms have their oxidation state changed. ** Organic redox reaction, a redox reacti ...

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 bacterium 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 Unicellular organism, unicellular and/or multicellular organisms other than by the ("vertical") transmission of DNA from parent to offsprin ...

s within the lineage. These factors lead many to believe the phylum of ''Aquifex'' is basal next to ''

Thermotogota The Thermotogota are a phylum of the domain Bacteria. The phylum Thermotogota is composed of Gram-negative staining, anaerobic, and mostly thermophilic and hyperthermophilic bacteria.Gupta, RS (2014) The Phylum Thermotogae. The Prokaryotes 989-10 ...

'', another hyperthermophilic phylum, or are a part of the

Campylobacterota Campylobacterota are a phylum of bacteria. All species of this phylum are Gram-negative. The Campylobacterota consist of few known genera, mainly the curved to spirilloid ''Wolinella'' spp., ''Helicobacter'' spp., and '' Campylobacter'' spp. Mos ...

, 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 catalyses the reversible oxidation of molecular hydrogen (H2), as shown below: Hydrogen uptake () is coupled to the reduction of electron acceptors such as oxygen, nitrate, sulfate, carbon dioxide (), and fumara ...

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