Geosmin

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Geosmin
Geosmin
IUPAC name 4,8a-dimethyldecalin-4a-ol or, (4S,4aS,8aR)-4,8a-dimethyl-1,2,3,4,5,6,7,8-octahydronaphthalen-4a-ol
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 CC1CCCC2(C1(CCCC2)O)C
InChI 1/C12H22O/c1-10-6-5-8-11(2)7-3-4-9-12(10,11)13/h10,13H,3-9H2,1-2H3

/t10-,11+,12-/m0/s1
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 disclaimer and 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. The human nose is extremely sensitive to geosmin, able to detect it at concentrations down to 5 parts per trillion.

Geosmin is produced by several classes of microbes, including cyanobacteria (blue-green algae) and actinobacteria especially though 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 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.[1][2] 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.

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[edit] References

  1. ^ 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. 
  2. ^ 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. 

[edit] Further reading