Aquifex

Genome structure

The complete genome for A. aeolicus consists of 1,551,335 base pairs with over 1500 open reading frames (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 operons. 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 autotrophic 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 oxidoreductases 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 transfers 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 hydrogenases 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

References

1. (2012-01-01). "Chapter Four – The Hyperthermophilic Bacterium Aquifex aeolicus: From Respiratory Pathways to Extremely Resistant Enzymes and Biotechnological Applications". Academic Press.
2. Olsen, Gary J.. (October 1994). "Archaea, Archaea, every where". Nature.
3. (2013-12-01). "Being Aquifex aeolicus: Untangling a Hyperthermophile's Checkered Past". Genome Biology and Evolution.
4. (2011-04-12). "Characterization of a unique [FeS] cluster in the electron transfer chain of the oxygen tolerant [NiFe] hydrogenase from Aquifex aeolicus". Proceedings of the National Academy of Sciences.
5. (2010-10-01). "Aquifex aeolicus membrane hydrogenase for hydrogen biooxidation: Role of lipids and physiological partners in enzyme stability and activity". International Journal of Hydrogen Energy.