Aquifex pyrophilus

Aquifex pyrophilus is a gram-negative, non-spore forming, rod-shaped bacteria with a length of 2 to 6 micrometers and a diameter of around half a micrometer. It is one of a handful of species in the Aquificota phylum- an unique group of thermophilic bacteria that are found near underwater volcanoes or hot springs.[1][2] A. pyrophilus is capable of surviving in extremely high temperatures and have shown resistance to ultraviolet light and ionizing radiation.[3] This has led to hypotheses that these bacteria evolved when the earth was still violently hot and had a thin atmosphere.[3] Further phylogenetic analyses on the basis of small-subunit rRNA sequence comparisons has led A. pyrophilus to be thought as some of the oldest species in the bacteria domain.[4][5] Aquifex pyrophilus was discovered at Kolbeinsey Ridge, North of Iceland by Robert Huber and Karl Stetter in 1992.[6]

Aquifex pyrophilus
Scientific classification
Domain:
Bacteria
Phylum:
Aquificota
Class:
Aquificia
Order:
Aquificales
Family:
Aquificaceae
Genus:
Aquifex
Species:
A. pyrophilus
Binomial name
Aquifex pyrophilus
Huber and Stetter, 1992

Name Meaning

Aquifex pyrophilus has a name that references its respiration and its habitat. The name "Aquifex" means "water-maker" in Latin. The name was assigned to A. pyrophilus because it typically uses oxygen as its respiration and water as a byproduct.[7] 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 habitat A. pyrophilus is typically found in.

Habitat
Kolbeinsey Ridge lies between Greenland, Iceland, and the Jan Mayen Microcontinent. This is the location where Aquifex pyrophilus was discovered. It is a submarine ridge that has high volcanic activity.

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 hot springs where temperatures are extremely high and pressure can be immense.[3] The Aquifex genus is rather intolerable to oxygen therefore it is only found in low-oxygenated environments. Despite this, Aquifex remains one of only aerobic bacterial hyperthermophiles known.[8] Near these hydrothermal vents and underwater volcanos, oxygen is limited because of the extremely high temperature and reducing power of volcanic gases like H2S. A. pyrophilus thrives where the oxic and anoxic zones meet in these environments because of the high availability of hydrogen and thiosulfate.[6]

In Huber's and Stetter's first analysis of the bacteria in 1992, 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 concentration of 3% (range of 1-5%).[6]

A. pyrophilus has eight polytrichously inserted flagella making it very motile in its environment.[6] A. pyrophilus can grow singly, in pairs, and/or form large cell conglomerations, comprising up to 100 individual cells.[6][9]

Metabolism
The Aquifex electron transport chain when growing in an aerobic environment.

A. pyrophilus is strictly chemolithoautotrophic.[6] It is capable of using oxygen in its respiration, but can also grow anaerobically by reducing nitrogen instead. In aerobic conditions, A. pyrophilus oxidizes molecular hydrogen and yields H2O and ATP. Other molecules that A. pyrophilus uses in aerobic conditions are S° and S2O32-.[6] In anaerobic conditions, A. pyrophilus uses nitrate reduction as an energy source. Molecular hydrogen, S°, and S2O32- are used as electron donors and oxygen and nitrate are used as electron acceptors.[6] During respiration, its byproducts include sulfuric acid from S° and S2O32- and hydrogen sulfide from S° and H2.[6]

Lineage and Phylogeny

A. pyrophilus has a relatively small genome. Out of the known thermophile genomes, A. pyrophilus is the smallest.[10] Due to its relatively small and simple genome, its ability to survive in extreme heat, its ability to be resistant toward ultraviolet light and ionizing radiation, and because of its 16S rRNA being sequenced directly from the PCR amplified gene, it is heavily accepted that they are some of the earliest bacteria that branched from archaea.[5]

There have been investigations of the phylogenetic position of Aquificales, the order of A. pyrophilus, through concatenated data of proteins shared within the Aquificales order. The results show that the Aquificales are most closely related to Thermotogales when observing whole-genome information.[11] Additionally, Aquificales were found to be somewhat closely related to ε-proteobacteria in phylogenetic trees.[11] 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.[5]

References
  1. "aquifex". web.archive.org. 2005-03-12. Retrieved 2022-09-13.
  2. Beblo, Kristina; Douki, Thierry; Schmalz, Gottfried; Rachel, Reinhard; Wirth, Reinhard; Huber, Harald; Reitz, Günther; Rettberg, Petra (2011-11-01). "Survival of thermophilic and hyperthermophilic microorganisms after exposure to UV-C, ionizing radiation and desiccation". Archives of Microbiology. 193 (11): 797–809. doi:10.1007/s00203-011-0718-5. ISSN 1432-072X.
  3. "4.5: Deeply Branching Bacteria". Biology LibreTexts. 2016-07-10. Retrieved 2022-10-11.
  4. Deckert, Gerard; Warren, Patrick V.; Gaasterland, Terry; Young, William G.; Lenox, Anna L.; Graham, David E.; Overbeek, Ross; Snead, Marjory A.; Keller, Martin; Aujay, Monette; Huber, Robert; Feldman, Robert A.; Short, Jay M.; Olsen, Gary J.; Swanson, Ronald V. (1998). "The complete genome of the hyperthermophilic bacterium Aquifex aeolicus". Nature. 392 (6674): 353–358. doi:10.1038/32831. ISSN 1476-4687.
  5. Burggraf, S.; Olsen, G. J.; Stetter, K. O.; Woese, C. R. (1992-08-01). "A Phylogenetic Analysis of Aquifex pyrophilus". Systematic and Applied Microbiology. 15 (3): 352–356. doi:10.1016/S0723-2020(11)80207-9. ISSN 0723-2020.
  6. Huber, Robert; Wilharm, Thomas; Huber, Dagmar; Trincone, Antonio; Burggraf, Siegfried; König, Helmut; Reinhard, Rachel; Rockinger, Ingrid; Fricke, Hans; Stetter, Karl O. (1992). "Aquifex pyrophilus gen. nov. sp. nov., Represents a Novel Group of Marine Hyperthermophilic Hydrogen-Oxidizing Bacteria". Systematic and Applied Microbiology. 15 (3): 340–351. doi:10.1016/S0723-2020(11)80206-7.
  7. "Aquifex pyrophilus - microbewiki". microbewiki.kenyon.edu. Retrieved 2022-09-12.
  8. PRATT, C (1997). "£24.95Michael T. Madigan, John M. Martinko and Jack Parker, Getting the bug for microorganisms (8th edn), , Prentice Hall (1997) ISBN 0 13 571 2254, p. 986". Trends in Cell Biology. 7 (9): 375–376. doi:10.1016/s0962-8924(97)83479-4. ISSN 0962-8924.
  9. Dworkin, Martin (1999). The Prokaryotes : an evolving electronic resource for the microbiological community. Springer-Verlag. ISBN 0-387-14254-1. OCLC 421690865.
  10. Shao, Z; Mages, W; Schmitt, R (1994). "A physical map of the hyperthermophilic bacterium Aquifex pyrophilus chromosome". Journal of Bacteriology. 176 (21): 6776–6780. doi:10.1128/jb.176.21.6776-6780.1994. ISSN 0021-9193.
  11. Oshima, Kenro; Chiba, Yoko; Igarashi, Yasuo; Arai, Hiroyuki; Ishii, Masaharu (2012-07-12). "Phylogenetic Position of Aquificales Based on the Whole Genome Sequences of Six Aquificales Species". International Journal of Evolutionary Biology. 2012: 1–9. doi:10.1155/2012/859264. ISSN 2090-8032.
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