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Geosmin
Geosmin
IUPAC name
Other names 4,8a-dimethyl-decahydronaphthalen-4a-ol

or, octahydro-4,8a-dimethyl-4a(2H)-naphthalenol

Identifiers
CAS number 19700-21-1
PubChem 29746
SMILES
InChI
Properties
Molecular formula C12H22O
Molar mass 182.30248 g/mol
Boiling point

270 to 271 °C @ 101.325 kPa

Hazards
Flash point 103.89 degrees Celsius
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Geosmin, which literally translates to "earth smell", is an organic compound with a distinct earthy flavour and aroma, and is responsible for the earthy taste of beets and a contributor to the strong scent that occurs in the air when rain falls after a dry spell of weather (petrichor) or when soil is disturbed[1]. The human nose is extremely sensitive to geosmin and is able to detect it at concentrations as low as 5 parts per trillion.

Geosmin is produced by several classes of microbes, including cyanobacteria (blue-green algae) and actinobacteria (especially streptomyces), and released when these microbes die. Communities whose water supply depends on surface water can periodically experience episodes of unpleasant-tasting water when a sharp drop in the population of these bacteria releases geosmin into the local water supply. Under acidic conditions, geosmin decomposes into odorless substances.

Geosmin is also responsible for the muddy smell in bottom-dwelling freshwater fish such as carp and catfish. Cyanobacteria produce geosmin and 2-methylisoborneol, which concentrate in the skin and dark muscle tissue. Geosmin breaks down in acid conditions; hence vinegar and other acidic ingredients in fish recipes help reduce the muddy flavor.

Recently, the biosynthesis of geosmin by a bifunctional Streptomyces coelicolor enzyme has been unravelled by Jiang et al.[2][3] A single enzyme, the germacradienol/germacrene D Synthase converts farnesyl diphosphate to geosmin in a two-step reaction.

Streptomyces coelicolor is the model representative of a group of soil-dwelling organisms with a complex lifecycle involving mycelial growth and spore formation. Beside the production of volatile geosmin, it also produces many other complex molecules of pharmacological interest and its genome sequence is available at the Sanger Institute.[4]

Contents

See also

References

  1. ^ http://www.expasy.org/spotlight/back_issues/035/
  2. ^ Jiang, J.; X. He, D.E. Cane (2006). "Geosmin biosynthesis. Streptomyces coelicolor germacradienol/germacrene D Synthase converts farnesyl diphosphate to geosmin". J. Am. Chem. Soc. 128 (25): 8128–8129. doi:10.1021/ja062669x.  
  3. ^ Jiang, J.; X. He, D.E. Cane (2007). "Biosynthesis of the earthy odorant geosmin by a bifunctional Streptomyces coelicolor enzyme". Nat. Chem. Biol. advanced online publication 3: 711. doi:10.1038/nchembio.2007.29.  
  4. ^ "The genome of Streptomyces coelicolor A3(2) producing geosmin". Sanger Institute. http://www.sanger.ac.uk/Projects/S_coelicolor/. Retrieved 2009-01-31.  

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