"''Aquifex aeolicus''" is a

chemolithoautotroph 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 ...

ic,

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 ...

, motile,

hyperthermophilic 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 ...

bacterium 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 ...

. "''A. aeolicus"'' is generally rod-shaped with an approximate length of 2.0-6.0μm and a diameter of 0.4-0.5μm. "''A. aeolicus''" is neither validly nor effectively published and, having no standing in nomenclature, should be styled in quotation marks. 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, an unusual group of thermophilic bacteria that are thought to be some of the oldest species of bacteria, related to filamentous bacteria first observed at the turn of the century. "''A. aeolicus''" is also believed to be one of the earliest diverging species of thermophilic bacteria. "''A. aeolicus''" grows best in water between 85 °C and 95 °C, and can be 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 c ...

s. It 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 has been found to grow optimally under

microaerophilic A microaerophile is a microorganism that requires environments containing lower levels of dioxygen than that are present in the atmosphere (i.e. < 21% O₂; typically 2–10% O₂) for optimal growth. A more r ...

conditions. Due to its high stability against high temperature and lack of oxygen, "''A. aeolicus''" is a good candidate for biotechnological applications as it is believed to have potential to be used as

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 fumarat ...

s in an attractive H2/O2 biofuel cell, replacing chemical catalysts. This can be useful for improving industrial processes.

Microbiological Characteristics

Morphology Mature "''A. aeolicus''" cells are typically rod-shaped bacterium with an approximate length of 2.0-6.0μm and a diameter of 0.4-0.5μm. These cells are motile by means of a monopolar polytrichous flagella. Additionally, members of the species tend to form large cell conglomerations, of up to 100 individual cells. "''A. aeolicus''" can display

pleomorphism Pleomorphism may refer to: * Pleomorphism (cytology), variability in the size and shape of cells and/or their nuclei * Pleomorphism (microbiology), the ability of some bacteria to alter their shape or size in response to environmental conditions ...

based on variation in the environment. Metabolism As an

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 Wo ...

, "''A. aeolicus''" has the ability to obtain all necessary carbon by fixing CO₂ from the environment and utilizes molecular hydrogen as an electron/energy source. Additionally, this bacterium utilizes a reductive

TCA cycle The citric acid cycle (CAC)—also known as the Krebs cycle or the TCA cycle (tricarboxylic acid cycle)—is a series of chemical reactions to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and protein ...

as it provides the substrates of many bio synthetic pathways. The "''A. aeolicus''"

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 g ...

contains encoding genes that together could constituent the TCA pathway:

fumarate reductase Fumarate reductase is the enzyme that converts fumarate to succinate, and is important in microbial metabolism as a part of anaerobic respiration. Succinate + acceptor fumarate + reduced acceptor Fumarate reductases can be divided into two classe ...

, fumarate hydratase,

isocitrate dehydrogenase Isocitrate dehydrogenase (IDH) () and () is an enzyme that catalyzes the oxidative decarboxylation of isocitrate, producing alpha-ketoglutarate (α-ketoglutarate) and CO2. This is a two-step process, which involves oxidation of isocitrate (a s ...

malate dehydrogenase Malate dehydrogenase () (MDH) is an enzyme that reversibly catalyzes the oxidation of malate to oxaloacetate using the reduction of NAD+ to NADH. This reaction is part of many metabolic pathways, including the citric acid cycle. Other malate ...

, ferredoxin

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 u ...

succinate Succinic acid () is a dicarboxylic acid with the chemical formula (CH2)2(CO2H)2. The name derives from Latin ''succinum'', meaning amber. In living organisms, succinic acid takes the form of an anion, succinate, which has multiple biological ro ...

- CoA

ligase In biochemistry, a ligase is an enzyme that can catalyze the joining (ligation) of two large molecules by forming a new chemical bond. This is typically via hydrolysis of a small pendant chemical group on one of the larger molecules or the enzym ...

, aconitase and citratesynthase. Moreover, this bacterium uses oxygen,

hydrogen Hydrogen is the chemical element with the symbol H and atomic number 1. Hydrogen is the lightest element. At standard conditions hydrogen is a gas of diatomic molecules having the formula . It is colorless, odorless, tasteless, non-toxic ...

, and mineral salts as its primary energy sources. "''A. aeolicus''" can also reduce nitrogen and sulfur. Regarding its growth under microaerophilic conditions, ''Aquifex'' species have been observed to grow in oxygen concentrations as long as 7.5ppm. It is hypothesized that this is possible because 1) their oxygen-respiration system was already highly developed before the advent of oxygenic

photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...

, 2) the ''Aquifex'' lineage came to life after there was a rise in atmospheric oxygen, or 3) oxygen respiration was developed, and then transferred among different bacterial lineages, such as ''Aquifex''. In response to oxidative stress, "''A. aeolicus''" possesses protective enzymes such as

superoxide In chemistry, a superoxide is a compound that contains the superoxide ion, which has the chemical formula . The systematic name of the anion is dioxide(1−). The reactive oxygen ion superoxide is particularly important as the product of t ...

and

peroxide In chemistry, peroxides are a group of compounds with the structure , where R = any element. The group in a peroxide is called the peroxide group or peroxo group. The nomenclature is somewhat variable. The most common peroxide is hydrogen ...

to counter harmful oxygen species.

Habitat

"''A. aeolicus''" was originally isolated from underwater volcanic vents near the Aeolic Islands (north of Sicily) and has also been isolated from the hot springs in Yellowstone. As a hyperthermophile, "''A. aeolicus''" can survive up to 95 °C with a temperature optima of 85 °C with a pH optima of 8.0, ranging from 6.8 to 9.0.

Genomic Properties

''"Aquifex aeolicus''" is the first thermophilic bacterium to have its entire genome encoded. Comparison of the "''Aquifex aeolicus''"

to other organisms showed that around 16% of its genes originated from 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 ...

domain Domain may refer to: Mathematics *Domain of a function, the set of input values for which the (total) function is defined **Domain of definition of a partial function **Natural domain of a partial function **Domain of holomorphy of a function * Do ...

. It is most closely related to the hydrogen-oxidizing bacterium, '' Aquifex pyrophilus'', and its close relative, ''

Hydrogenobacter thermophilus ''Hydrogenobacter thermophilus'' is an extremely thermophilic, straight rod (bacillus) bacterium. TK-6 is the type strain for this species. It is a Gram negative, non-motile, obligate chemolithoautotroph. It belongs to one of the earliest bran ...

''. The genome of "''A. aeolicus''" has been successfully mapped, but was noted to be only one-third the size of the '' E. coli''genome. The genome of "''A. aeolicus''" is densely packed while no introns or protein splicing elements were found. It possesses a circular chromosome with 1,551,335 bp and has a

G+C content G, or g, is the seventh letter in the Latin alphabet, used in the modern English alphabet, the alphabets of other western European languages and others worldwide. Its name in English is ''gee'' (pronounced ), plural ''gees''. History Th ...

of 43.4%, and contains 1,796 genes. It also contains genes potentially coding for three distinct iFe

s, however, it is thought that the ''Aquifex''hydrogenases I and II function in energy conservation, where as hydrogenase III is more likely required for CO₂fixation. Additionally, during sequencing, a single extra chromosomal element (ECE) was identified, suggesting evidence of genetic exchange between the "''A. aeolicus''"

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins are ...

and the ECE.

Industrial Applications

Multiple enzymes have been identified for potential future use due to their high stability and capacity to oxidize molecular hydrogen, producing byproducts of heat and water. A key enzyme of note is Hydrogenase I which was used to study the relationship of enzymes and electrodes during the development of H2-fed, energy-generating biofuel cells. Researchers have explored the use of another extremely resistant enzyme known as lumazine synthase. The cage-forming enzyme has been explored as potential drug delivery nano carrier as it was engineered to encapsulate other molecules.

References

External links

Aquifex aeolicus VF5 Genome
{{Taxonbar, from=Q4034249 Aquificota Bacteria described in 1992