Aquifex aeolicus

"Aquifex aeolicus" is a chemoautotrophic, Gram-negative, motile, generally rod-shaped bacterium with an approximate length of 2.0-6.0μm and a diameter of 0.4-0.5μm.[1] "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 Aquificae 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.[2] "A. aeolicus" grows best in water between 85 °C and 95 °C, and can be found near underwater volcanoes or hot springs. It requires oxygen to survive but has been found to grow optimally under microaerophilic conditions.[1] 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 hydrogenases in an attractive H2/O2 biofuel cell, replacing chemical catalysts.[3] This can be useful for improving industrial processes.

Aquificeae
Scientific classification
Domain:
Bacteria
Phylum:
Aquificae
Class:
Aquificae
Order:
Aquificales
Family:
Aquificaceae
Genus:
Aquifex
Species:
A. aeolicus
Binomial name
"Aquifex aeolicus"
Huber and Stetter, 1992 - NB: Neither validly nor effectively published.

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.[1] These cells are motile by means of a monopolar polytrichous flagella.[1] Additionally, members of the species tend to form large cell conglomerations, of up to 100 individual cells.[3]

Metabolism

As an autotroph, "A. aeolicus" has the ability to obtain all necessary carbon by fixing CO2 from the environment.[4] Additionally, this bacterium utilizes the TCA cycle as it provides the substrates of many bio synthetic pathways. The "A. aeolicus" genome contains encoding genes that together could constituent the TCA pathway: fumarate reductase, fumarate hydratase, isocitrate dehydrogenase, malate dehydrogenase, ferredoxin oxidoreductase, succinate-CoA ligase, aconitase and citratesynthase.[1] Moreover, this bacterium uses oxygen, hydrogen, and mineral salts as its primary energy sources.

Regarding its growth under microaerophilic conditions, Aquifex species have been observed to grow in oxygen concentrations as long as 7.5ppm.[2] It is hypothesized that this is possible because 1) their oxygen-respiration system was already highly developed before the advent of oxygenic photosynthesis, 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.[1]

Environment

"A. aeolicus" was first discovered in the outflow of hot springs in Yellowstone National Park.[2] However, it was also found growing near underwater volcanoes around the Aeolian Islands, north of Sicily.[1] As a thermophilic, "A. aeolicus" grows best in water between 85 °C and 95 °C,[4] with a pH optima of 8.0, ranging from 6.8 to 9.0.

Phenotypic and Genetic Characteristics

Comparison of the "Aquifex aeolicus" genome to other organisms showed that around 16% of its genes originated from the Archaea domain. It is most closely related to the hydrogen-oxidizing bacterium, Aquifex pyrophilus, and its close relative, Hydrogenobacter thermophilus.[2]

The genome of "A. aeolicus" has been successfully mapped,[1] but was noted to be only one-third the size of the E. coli genome. As a result of the limited genome size, metabolic flexibility seemed to reduce. It has the smallest genome of any known non-parasite. Its total genome is 1.5 Mb long, has a G+C content of 43.4%, and contains 1512 genes. It also contains genes potentially coding for three distinct [NiFe] hydrogenases, however, it is thought that the Aquifex hydrogenases I and II function in energy conservation, where as hydrogenase III is more likely required for CO2 fixation.[4] Additionally, during sequencing, a single extra chromosomal element (ECE) was identified,[1] suggesting evidence of genetic exchange between the "A. aeolicus" chromosome and the ECE.

References
  1. Huber, R., Swanson, R., Deckert, G., Warren, P., Gaasterland, T., Young, W., Lenox, A., Graham, D. (1998). "The complete genome of the hyperthermophilic bacterium Aquifex aeolicus". Nature. 392 (6674): 353–8. Bibcode:1998Natur.392..353D. doi:10.1038/32831. PMID 9537320.CS1 maint: multiple names: authors list (link)
  2. Reysenbach, L., Wickham, G. S. & Pace, N. R. (1994). "Phylogenetic analysis of the hyperthermophilic pink filament community in Octopus Spring, Yellowstone National Park". Applied and Environmental Microbiology. 60 (6): 2113–2119. doi:10.1128/AEM.60.6.2113-2119.1994. PMC 201609. PMID 7518219.CS1 maint: multiple names: authors list (link)
  3. Guiral, M; Prunetti, L; Aussignargues, C; Ciaccafava, A; Infossi, P; Ilbert, M; Lojou, E; Giudici-Orticoni, M. T. (2012). "The Hyperthermophilic Bacterium Aquifex aeolicus". The hyperthermophilic bacterium Aquifex aeolicus: From respiratory pathways to extremely resistant enzymes and biotechnological applications. Advances in Microbial Physiology. 61. pp. 125–94. doi:10.1016/B978-0-12-394423-8.00004-4. ISBN 9780123944238. PMID 23046953.
  4. Brugna-Guiral, M., Tron, P., Nitschke, W., Stetter, K., Burlat, B., Guigliarelli, B., Bruschi, M., Giudici-Orticoni, M. (2003). "[NiFe] hydrogenases from the hyperthermophilic bacterium Aquifexa eolicus: properties, function, and phylogenetics". Extremophiles. 7 (2): 145–157. doi:10.1007/s00792-002-0306-3. PMID 12664267. S2CID 29969302.CS1 maint: multiple names: authors list (link)
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