|Jmol-3D images||Image 1|
|Molar mass||182.30 g mol−1|
|Boiling point||270 to 271 °C; 518 to 520 °F; 543 to 544 K|
|Flash point||104 °C; 219 °F; 377 K|
| (what is: / ?)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
Geosmin is an organic compound with a distinct earthy flavor and aroma, and is responsible for the earthy taste of beets and a contributor to the strong scent (petrichor) that occurs in the air when rain falls after a dry spell of weather or when soil is disturbed. It is produced by a type of Actinobacteria. In chemical terms, it is a bicyclic alcohol with formula C12H22O, a derivative of decalin. Its name is derived from the Greek γεω- "earth" and ὀσμή "smell".
Geosmin is produced by the gram-positive bacteria Streptomyces, a genus of Actinobacteria in the order Actinomycetales, and released when these microorganisms die. Communities whose water supplies depend 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.
In 2006, the biosynthesis of geosmin by a bifunctional Streptomyces coelicolor enzyme was unravelled. A single enzyme, geosmin synthase, converts farnesyl diphosphate to geosmin in a two-step reaction.
Streptomyces coelicolor is the model representative of a group of soil-dwelling bacteria with a complex lifecycle involving mycelial growth and spore formation. Besides the production of volatile geosmin, it also produces many other complex molecules of pharmacological interest; its genome sequence is available at the Sanger Institute.
Geosmin 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. 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 responsible for the muddy smell in many commercially important freshwater fish such as carp and catfish. Geosmin combines with 2-methylisoborneol, which concentrates in the fatty skin and dark muscle tissues. Geosmin breaks down in acid conditions; hence, vinegar and other acidic ingredients are used in fish recipes to help reduce the muddy flavor.
- Gerber, NN; Lechevalier, HA (November 1965). "Geosmin, an earthly-smelling substance isolated from actinomycetes.". Applied microbiology 13 (6): 935–8. PMC 1058374. PMID 5866039.
- 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.
- 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.
- "The genome of Streptomyces coelicolor A3(2) producing geosmin". Sanger Institute. Retrieved 2009-01-31.
- The earth's perfume, Protein Spotlight, Issue 35, June 2003.
- Polak, E.H.; Provasi, J. (1992). "Odor sensitivity to geosmin enantiomers". Chemical Senses 17: 23. doi:10.1093/chemse/17.1.23.
- Yuhas, Daisy (18 July 2012). "Storm Scents: You Can Smell Oncoming Rain". Scientific American.