Sulfolobus solfataricus
Timothy A. Becker
Environments that are considered by man to be extreme are colonized by special microorganisms, which are adapted to these ecological niches. These organisms are called extremophiles and may be divided into five categories: thermophiles, acidophiles, alkaliphiles, halophiles and psychrophiles, clearly indicating the nature of habitats used by these microorganisms. These habitats include hot springs, shallow submarine hydrothermal systems or abyssal hot-vent systems where microorganisms can be found at temperatures above 100 C. Extremophiles are also found in high saline lakes, sometimes at salt conditions near that of saturation, and in environments with extreme pH values, either acidic (acidic solfatara fields and acidic sulfur pyrite areas), or alkaline (freshwater, alkaline hot springs, carbonate springs, alkaline soils and soda lakes). The habitats of psychrophilic organisms include the cold polar seas and soils, and Alpine glaciers, as well as deep-sea sediments which are not only permanently cold but at high pressure. Usually, extremophilic microorganisms live in biotopes combining several stress factors, for instance high temperature and acidic conditions. It would not be too outrageous to speculate that wherever there is an extreme environment, there very likely are extremophiles, microorganisms at the frontiers of life.

Hyperthermophiles are microorganisms that grow optimally between 80'C and 105'C (and up to 110 C). Most of them belong to the domain Archaea, a unique assemblage that is evolutionarily remote and fundamentally different from Bacteria with respect to biochemistry, physiology and molecular biology. Hypertherrnophiles are an important source of thermostable enzymes for the industry. Several genome sequencing projects directed at prokaryotes that have been reported mainly concern Bacteria. The genome project on the hyperthermophilic (opt. 85'C), acidophilic (opt. pH 3), aerobic archaeon, Sulfolobus solfataricus, was initiated in early 1994 in Canada. The 3.1 Mbp genome of' S. solfataricus were selected not only because of its distance from bacterial genomes but also because of it is AT rich (36% G+C ) and thus easy to sequence; a strong potential exists for the development of good tools for genetic analysis.

S. solfataricus is a member of the Crenarchaeota, which contains mainly organisms that grow in extreme conditions (i.e., high temperature, low pH) S. solfataricus have coccoid cells that are highly irregular in shape and have strong lobes. It is found in sulfurous caldrons a t high temperatures and various acidic pH's , and grows only in the presence of oxygen. The strain that is being completely sequenced was isolated from a volcanic hot spring . It typically appears as an iridescent, oily, glimmering layer on mud or water. In culture, S. solfataricus grows at temperatures between 50 and 87 C and a pH between 3.5 and 5. Like all members of its order it is capable of oxidizing elemental sulfur to sulfuric acid. There are many potential industrial applications for S. solfataricus, using its ability to oxidize sulfur and dissolve pyrite, and as a source for enzymes that are resistant to high t temperatures and organic solvents. S. solfataricus has a chromosome about 3.1 Mb, among the largest in the Archaea. The average G+C content is 37% which is uniquely low since the usual way of thermostabilizing genetic material is to have a high G+C/A+T ratio. S. solfataricus has a variable response to the Gram stain. As of April 1996, more than 800 Kb of the S. solfataricus genome has been sequenced. In the analyzed portion of the sequence, there are 491 open reading frames that are likely to correspond to genes, and nine tRNA genes. The open reading frames occur approximately every Kb suggesting numerous enzymes are yet to be discovered.


*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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