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
ChemSpider	27642 Y
ChEBI	CHEBI:46702 Y
Jmol-3D images	Image 1
SMILES O[C@]12[C@H](CCC[C@]2(CCCC1)C)C
InChI InChI=1S/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 Y Key: JLPUXFOGCDVKGO-TUAOUCFPSA-N Y 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	182.3 g mol−1
Boiling point	270 to 271 °C @ 101.325 kPa
Hazards
Flash point	103.89 degrees Celsius
Y (verify) (what is: Y/N?) 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.^[2]

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.^[3]

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.

In 2006, the biosynthesis of geosmin by a bifunctional Streptomyces coelicolor enzyme was unravelled by Jiang et al.^[4][5] 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.^[6]

See also

• Petrichor
• Streptomyces coelicolor

References

1. ^ The earth's perfume, Protein Spotlight, Issue 35, June 2003
2. ^ Polak, E.H.; Provasi, J. (1992). "Odor sensitivity to geosmin enantiomers". Chemical Senses 17: 23. doi:10.1093/chemse/17.1.23. 
3. ^ Gerber, NN; Lechevalier, HA (November 1965). "Geosmin, an earthly-smelling substance isolated from actinomycetes.". Applied microbiology 13 (6): 935–8. PMC 1058374. PMID 5866039. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1058374. 
4. ^ 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. PMID 16787064. 
5. ^ 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 (11): 711–5. doi:10.1038/nchembio.2007.29. PMC 3013058. PMID 17873868. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=3013058. 
6. ^ "The genome of Streptomyces coelicolor A3(2) producing geosmin". Sanger Institute. http://www.sanger.ac.uk/Projects/S_coelicolor/. Retrieved 2009-01-31. 

Further reading

• Bear, I.J.; R.G. Thomas (1964). "Nature of argillaceous odour". Nature 201 (4923): 993–995. doi:10.1038/201993a0. 

• Bear, I.J.; R.G. Thomas (1965). "Petrichor and plant growth". Nature 207 (5005): 1415–1416. doi:10.1038/2071415a0. 

External links

• Geosmin at PubChem