Aquifex aeolicus
Helen Cardwell

I chose to do my report on Aquifex aeolicus due to its versatility in biotechnological applications. Aquifex aeolicus is both hyperthermophilic and microaerophilic, making it unique in its resistance to heat and oxygen. This organism is further evolutionarily and physiologically interesting as one of the earliest diverging bacteria known, as well as being one of the most thermophilic organisms known (despite the small number of heat-resistant indicators in the genome). Moreover, A. aeolicus helps in ascertaining information about early protein synthesis through analysis of some of its RNA modification enzymes.

Aquifex aeolicus survives best at temperatures around 80 degrees Celsius and can survive up to 95 degrees C. Along with Aquifex pyrophilus, it is one of the most thermophilic bacteria known. It is an obligate chemoautotrophic bacterium, meaning it only derives energy from inorganic compounds. This Gram-negative eubacterium does not form spores. It does perform biotin biosynthesis. Biotin is a water-soluble vitamin essential for fatty acid biosynthesis and catabolism. Biotin is a growth factor for many cells; it is also known as vitamin B7.

This bacterium is rod-shaped, 2-6 micrometers long and .4-.5 micrometers in diameter. It forms cell conglomerations of up to 100 cells. A. aeolicus is motile, using monopolar, polytichous flagella. There have been more than 25 gene-encoding proteins identified in this organism involved in the structure and biosynthesis of the flagella. The genome of the A. aeolicus is about one third that of the E. coli in size. No introns or protein splicing elements have been discovered in the genome. One result of this limited size of the genome seems to be a limited of metabolic flexibility; it is an obligate chemolithotroph and microaerophile. Sixteen percent of its genes originate from Archea. An A. aeolicus bacterium contains one DNA molecule (a circular chromosome) and a single extrachromosomal element. The superfluous nature of the extrachromosomal unit and the chromosome suggests a possible genetic exchange between the two.

This microaerophilic organism can grow in environments with oxygen levels as low as 7.5ppm. This is thought to show that A. aeolicus developed its oxygen-respiration system when there was significantly less oxygen present in the atmosphere. Oxygen serves as the final electron acceptor of its respiration, where it oxidizes hydrogen gas. This is possible by the presence of a complex respiratory apparatus. The final product of its respiration is water, giving it the genus Aquifex (“water maker”). A. aeolicus can reduce and fix both nitrogen and sulfur. Unlike A. pyrophilus, it does not perform NO3- respiration and cannot grow anaerobically on nitrogen despite the presence of a putative nitrate reductase in the genome.

A. aeolicus can grow on hydrogen, oxygen, carbon dioxide and mineral salts.  It contains three thermostable and oxygen tolerant hydrogenases. Two of the hydrogenases serve in energy conservation (these two are membrane-bound periplasmic hydrogenases). The third, soluble cytoplasmic hydrgogenase is most likely involved in the carbon dioxide fixation pathway.

R. Huber and K.O. Stetter isolated this bacterium in underwater volcanic vents in the Aeolic Islands (hence the special name aeolicus) north of Sicily. It was also isolated in the hot springs of Yellowstone National Park.

References

“Aquifex aeolicus.” MicrobeWiki: Microbial Biorealm. <<http://microbewiki.kenyon.edu/index.php/Aquifex_aeolicus>>

“Aquifex aeolicus VF5.” NCBI <<http://www.ncbi.nlm.nih.gov/Taxonomy/Browser/
wwwtax.cgi?mode=Info&id=224324&lvl=3&lin=f&keep=1&srchmode=1&unlock>>

“The complete genome of the hyperthermophilic bacterium Aquifex aeolicus.Nature: International Weekly Journal of Science. 392, 353-358 (26 March 1998) | doi:10.1038/32831; Received 26 August 1997; Accepted 3 February 1998 <<http://www.nature.com/nature/journal/v392/n6674/full/392353a0.html>>

“Genome Properties Report: Selected Organism: Aquifex aeolicus VF5.” JCVI- Comprehensive Microbial Resource.
<<http://cmr.jcvi.org/tigr-scripts/CMR/shared/GenomeProperties.cgi?sub_org=
Aquifex%20aeolicus%20VF5%21&sub_org_val=ntaa01%21&states_text=All+Genome+Properties&states=
all&org=ntaa01states_box=all>>

*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.

 

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