Wikipedia

Geosmin

Geosmin (/dʒiˈɒzmɪn/ jee-OZ-min) is an irregular sesquiterpenoid with a distinct earthy or musty odor, which most people can easily smell. The geosmin odor detection threshold in humans is very low, ranging from 0.006 to 0.01 micrograms per liter in water.[1] Geosmin, along with the irregular monoterpene 2-methylisoborneol, together account for the majority of biologically-caused taste and odor outbreaks in drinking water worldwide and in farmed fish.[1][2] Geosmin is also responsible for the earthy taste of beetroots and a contributor to the strong scent, known as petrichor, that occurs when rain falls after a spell of dry weather or when soil is disturbed.[3]

Geosmin
Geosmin
Names
Preferred IUPAC name
(4S,4aS,8aR)-4,8a-Dimethyloctahydronaphthalen-4a(2H)-ol
Other names
(4S,4aS,8aR)-4,8a-Dimethyl-1,2,3,4,5,6,7,8-octahydronaphthalen-4a-ol; 4,8a-Dimethyl-decahydronaphthalen-4a-ol; Octahydro-4,8a-dimethyl-4a(2H)-naphthalenol
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.039.294 Edit this at Wikidata
UNII
  • 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 checkY
    Key: JLPUXFOGCDVKGO-TUAOUCFPSA-N checkY
  • 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
  • O[C@]12[C@H](CCC[C@]2(CCCC1)C)C
Properties
C12H22O
Molar mass 182.307 g·mol−1
Melting point 78 to 82 °C (172 to 180 °F; 351 to 355 K)
Boiling point 270 to 271 °C (518 to 520 °F; 543 to 544 K)
Hazards
Flash point 104 °C (219 °F; 377 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

In chemical terms, geosmin is a bicyclic alcohol with formula C12H22O, a derivative of decalin. It is produced from the universal sesquiterpene precursor farnesyl pyrophosphate (also known as farnesyl diphosphate), in a two-step Mg2+-dependent reaction.[4] Its name is derived from the Ancient Greek words geō- (γεω-), meaning "earth", and osmḗ (ὀσμή), meaning "smell". The word was coined in 1965 by the American biochemist Nancy N. Gerber (1929–1985) and the French-American biologist Hubert A. Lechevalier (1926–2015).[5][6]

Production

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Geosmin is produced as a secondary metabolite by various blue-green algae (cyanobacteria), filamentous bacteria in the class Actinomyces, other prokaryotes, and various eukaryotes. The main genera in the cyanobacteria that have been shown to produce geosmin include Anabaena, Phormidium, and Planktothrix, while the main genus in the Actinomyces that produces geosmin is Streptomyces.[1][7][8][9] In beetroots, geosmin is produced endogenously, not by environmental nor endophytic microbes, suggesting beets possess separate or acquired means of geosmin biosynthesis.[10] 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.[5]

In 2006, geosmin was biosynthesized by a bifunctional Streptomyces coelicolor enzyme.[11][12] A single enzyme, geosmin synthase, converts farnesyl diphosphate to geosmin in a two-step reaction.

Not all blue-green algae produce geosmin. Identification of species that might produce geosmin is traditionally done through microscopic identification of algae as geosmin producers, a technique that is labor-intensive and requires specialized knowledge. Recent advances in molecular biology have enabled identification of a geosmin synthase gene, geoA, which is present in cyanobacterial species that produce geosmin, but is not present in other cyanobacterial species.[13] Amplification of this gene from water samples using real-time PCR may permit predictions of taste and odor events caused by cyanobacteria in fresh water.

Effects

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The human olfactory system is extremely sensitive to geosmin and is able to detect it at concentrations as low as anywhere from 0.4 parts per billion[14] to 5 parts per trillion.[15] It is proposed that this extreme sensitivity to geosmin evolved in humans or their ancestors to aid them in their search for scarce water, but this is not conclusive.[16] Similarly, many insects possess a sensitivity to geosmin such that it may act as an attractant, signaling the presence of microbial prey, or as a repellant, where its presence may coincide with that of toxin-producing microbes.[16] Geosmin is also implicated in the migratory patterns of eels, where its higher concentration in freshwater systems guides the fish from the ocean into estuaries and rivers.[17] Geosmin is also likely involved in raccoon predation of turtle nests, where burrowing disturbs the soil and ejects the chemical and other volatile indicators into the air.[18]

Geosmin is responsible for the muddy smell in many commercially important freshwater fish such as carp, catfish, and tilapia.[19][2][20] Geosmin combines with 2-methylisoborneol, which concentrates in the fatty skin and dark muscle tissues. It breaks down in acid conditions; hence, vinegar and other acidic ingredients are used in fish recipes to reduce the muddy flavor.[21] Taste and odor compounds including geosmin lead to an unpleasant taste of drinking water which is perceived by consumers as an indication of poor water quality.[22] Despite its negative effects on the taste and odor of fish and drinking water, geosmin is nontoxic to humans.[23]

This compound is reported to be an issue for saltwater fish farmed in recirculating aquaculture systems, such as Atlantic salmon,[24][citation needed] but there are also studies that show that the presence in seawater is significantly lower than that found in freshwater which is why many people consider freshwater fish to taste muddy compared to marine fish. These systems rely on biological filtration using cultured microbial communities to process the nitrogenous waste from the fish (ammonia) into less harmful compounds (nitrite and nitrate) that can be tolerated at higher concentrations. However, geosmin-producing bacteria can also grow in these systems, and often require fish to be transferred to an additional "finishing" or "purge" system where they are not fed for several days prior to harvest to remove off-flavor compounds and empty the intestinal tract.[citation needed] This process is also known as depuration.

Geosmin remediation in drinking water

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According to municipal water treatment facilities, geosmin cannot be removed from water using standard treatment processes.[25] Treating for geosmin requires additional treatment,[26] which may not be available to all municipal water suppliers. Activated carbon filters may be able to help somewhat, but few studies have been completed to address this issue.[27]

See also

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  • Dimethyl sulfide – One of the molecules responsible for the odour of the sea
  • Petrichor – Earthy smell when rain falls on dry soil

References

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  1. ^ a b c Jüttner, Friedrich; Watson, Susan B. (July 2007). "Biochemical and Ecological Control of Geosmin and 2-methylisoborneol in Source Waters". Applied and Environmental Microbiology. 73 (14): 4395–4706. Bibcode:2007ApEnM..73.4395J. doi:10.1128/AEM.02250-06. PMC 1932821. PMID 17400777. S2CID 1954489.
  2. ^ a b Lovell, R. T.; Lelana, I. Y.; Boyd, C. E.; Armstrong, M. S. (May 1986). "Geosmin and Musty-Muddy Flavors in Pond-Raised Channel Catfish". Transactions of the American Fisheries Society. 115 (3): 485–489. Bibcode:1986TrAFS.115..485L. doi:10.1577/1548-8659(1986)115<485:gamfip>2.0.co;2. ISSN 0002-8487.
  3. ^ "The earth's perfume". Protein Spotlight (35). June 2003.
  4. ^ Watson, W.; Juttner, F. (2019). Taste and Odour in Source and Drinking Water: Causes, Controls, and Consequences. IWA Publishing. ISBN 9781780406657.
  5. ^ a b Gerber, N. N.; Lechevalier, H. A. (November 1965). "Geosmin, an earthly-smelling substance isolated from actinomycetes". Applied Microbiology. 13 (6): 935–938. doi:10.1128/am.13.6.935-938.1965. PMC 1058374. PMID 5866039.
  6. ^ "geosmin". Merriam-Webster Dictionary. 22 May 2023.
  7. ^ Izaguirre, G.; Taylor, W. D. (2004). "A guide to geosmin- and MIB-producing cyanobacteria in the United States". Water Science and Technology. 49 (9): 19–24. doi:10.2166/wst.2004.0524. PMID 15237602.
  8. ^ Zaitlin, B.; Watson, S. B. (2006). "Actinomycetes in relation to taste and odour in drinking water: Myths, tenets and truths". Water Research. 40 (9): 1741–1753. Bibcode:2006WatRe..40.1741Z. doi:10.1016/j.watres.2006.02.024. PMID 16600325.
  9. ^ Suurnäkki, S.; Gómez Sáez, G. V.; Rantala-Ylinen, A.; Jokela, J.; Fewer, D. P.; Sivonen, K. (2015). "Identification of geosmin and 2-methylisoborneol in cyanobacteria and molecular detection methods for the producers of these compounds". Water Research. 68 (1): 56–66. Bibcode:2015WatRe..68...56S. doi:10.1016/j.watres.2014.09.037. PMID 25462716.
  10. ^ Hanson, Solveig J; Dawson, Julie C; Goldman, Irwin L (2021-09-29). "Beta vulgaris ssp. vulgaris chromosome 8 shows significant association with geosmin concentration in table beet". G3: Genes, Genomes, Genetics. 11 (12). doi:10.1093/g3journal/jkab344. ISSN 2160-1836. PMC 8664477. PMID 34586384.
  11. ^ Jiang, J.; He, X.; Cane, D. E. (2006). "Geosmin biosynthesis. Streptomyces coelicolor germacradienol/germacrene D synthase converts farnesyl diphosphate to geosmin". Journal of the American Chemical Society. 128 (25): 8128–8129. doi:10.1021/ja062669x. PMID 16787064.
  12. ^ Jiang, J.; He, X.; Cane, D. E. (2007). "Biosynthesis of the earthy odorant geosmin by a bifunctional Streptomyces coelicolor enzyme". Nature Chemical Biology. 3 (11): 711–715. doi:10.1038/nchembio.2007.29. PMC 3013058. PMID 17873868.
  13. ^ Kutovaya, O.; Watson, S. (2014). "Development and application of a molecular assay to detect and monitor geosmin-producing cyanobacteria and actinomycetes in the Great Lakes". Journal of Great Lakes Research. 40 (2): 404–414. Bibcode:2014JGLR...40..404K. doi:10.1016/j.jglr.2014.03.016.
  14. ^ Polak, E.H.; Provasi, J. (1992). "Odor sensitivity to geosmin enantiomers". Chemical Senses. 17: 23–26. doi:10.1093/chemse/17.1.23.
  15. ^ "Geosmin". American Chemical Society. Retrieved 2024-10-15.
  16. ^ a b Garbeva, Paolina; Avalos, Mariana; Ulanova, Dana; van Wezel, Gilles P.; Dickschat, Jeroen S. (Sep 2023). "Volatile sensation: The chemical ecology of the earthy odorant geosmin". Environmental Microbiology. 25 (9): 1565–1574. doi:10.1111/1462-2920.16381. hdl:1887/3719502. ISSN 1462-2912. PMID 36999338.
  17. ^ Tosi, Laura; Sola, Carla (1993-01-12). "Role of Geosmin, a Typical Inland Water Odour, in Guiding Glass Eel Anguilla anguilla (L.) Migration". Ethology. 95 (3): 177–185. doi:10.1111/j.1439-0310.1993.tb00468.x. ISSN 0179-1613.
  18. ^ Edmunds, Sarah E.; Kasparov, Christine N.; Yoon, Jae Byeok; Kanonik, Alexandra K.; Burke, Russell L. (2018). "Twelve Years Later: Reassessing Visual and Olfactory Cues Raccoons Use to Find Diamondback Terrapin Nests". Journal of Herpetology. 52 (3): 307–312. doi:10.1670/17-029. ISSN 0022-1511.
  19. ^ Vallod, D.; Cravedi, J. P.; Hillenweck, A.; Robin, J. (April 2007). "Analysis of the off-flavor risk in carp production in ponds in Dombes and Forez (France)". Aquaculture International. 15 (3–4): 287–298. Bibcode:2007AqInt..15..287V. doi:10.1007/s10499-007-9080-7. ISSN 0967-6120. S2CID 6669343.
  20. ^ Yamprayoon, Jirawan; Noomhorm, Athapol (2000). "Geosmin and Off-Flavor in Nile Tilapia (Oreochromis niloticus)". Journal of Aquatic Food Product Technology. 9 (2): 29–41. Bibcode:2000JAFPT...9b..29Y. doi:10.1300/J030v09n02_04. ISSN 1049-8850. S2CID 85598428.
  21. ^ Winkler, L. (2012). Westwood Lake Chronicles. Lawrence Winkler. ISBN 9780991694105.
  22. ^ Bristow, R. L.; Young, I. S.; Pemberton, A.; Williams, J.; Maher, S. (2019). "An extensive review of the extraction techniques and detection methods for the taste and odour compound geosmin (trans-1,10-dimethyl-trans-9-decalol) in water". Trends in Analytical Chemistry. 110: 233–248. doi:10.1016/j.trac.2018.10.032.
  23. ^ Mochida, Kyo (2009). "Evaluation of the Cytotoxicity of Geosmin and 2-Methylisoborneol Using Cultured Human, Monkey, and Dog Cells". Biocontrol Science. 14 (1): 35–38. doi:10.4265/bio.14.35. PMID 19344097.
  24. ^ Burr, Gary S.; Wolters, William R.; Schrader, Kevin K.; Summerfelt, Steven T. (2012-09-01). "Impact of depuration of earthy-musty off-flavors on fillet quality of Atlantic salmon, Salmo salar, cultured in a recirculating aquaculture system". Aquacultural Engineering. 50: 28–36. Bibcode:2012AqEng..50...28B. doi:10.1016/j.aquaeng.2012.03.002. ISSN 0144-8609.
  25. ^ Bruce, Darlene; Westerhoff, Paul; Brawley-Chesworth, Alice (2002-06-01). "Removal of 2-methylisoborneol and geosmin in surface water treatment plants in Arizona". Journal of Water Supply: Research and Technology-Aqua. 51 (4): 183–198. doi:10.2166/aqua.2002.0016. ISSN 0003-7214.
  26. ^ Elhadi, S. L. N.; Huck, P. M.; Slawson, R. M. (2004). "Removal of geosmin and 2-methylisoborneol by biological filtration". Water Science and Technology. 49 (9): 273–280. doi:10.2166/wst.2004.0586. ISSN 0273-1223. PMID 15237635.
  27. ^ Kim, Keug Tae (27 February 2021). "Geosmin and 2-MIB Removal by Full-Scale Drinking water Treatment Processes in the Republic of Korea". Water. 13 (5): 628. doi:10.3390/w13050628 – via mdpi.com.

Further reading

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