Volatile sensation: The chemical ecology of the earthy odorant geosmin

Abstract

Geosmin may be the most familiar volatile compound, as it lends the earthy smell to soil. The compound is a member of the largest family of natural products, the terpenoids. The broad distribution of geosmin among bacteria in both terrestrial and aquatic environments suggests that this compound has an important ecological function, for example, as a signal (attractant or repellent) or as a protective specialized metabolite against biotic and abiotic stresses. While geosmin is part of our everyday life, scientists still do not understand the exact biological function of this omnipresent natural product. This minireview summarizes the current general observations regarding geosmin in prokaryotes and introduces new insights into its biosynthesis and regulation, as well as its biological roles in terrestrial and aquatic environments.

Enantioselective synthesis of all stereoisomers of geosmin and of biosynthetically related natural products

“…The formation of 38 is explainable by an alternative reprotonation of the neutral intermediate 4 at C1 and capture of water. Several aspects of the chemical ecology of geosmin are known, 60 e.g. geosmin is a constituent of the defence secretions of the polydesmid millipede Niponia nodulosa , 61 it repells the bacterial predator Caenorhabditis elegans and reduces its grazing on streptomycetes, 62 but attracts springtails feeding on bacteria which promotes spore dispersal.…”

Lentzea sokolovensis sp. nov., Lentzea kristufekii sp. nov. and Lentzea miocenica sp. nov., rare actinobacteria from Miocene lacustrine sediment of the Sokolov Coal Basin, Czech Republic

“…Terpenes were the most abundant type of BGCs with two clusters for geosmin (100 % homology) [48,49], being present in all strains. Geosmin is a volatile, earthy-smelling, interspecies signalling molecule [48,49] that seems to have a very important role in spore dispersion of Streptomyces species [50]. All of our strains also carry a BGC for the production of coelichelin (72 % homology) a siderophore with high affinity for iron [51]; a BGC for RiPP:Lanthipeptide class III (75 % homology), which probably codes for the synthesis of various Ery-9 molecules, as well as a BGC for ε-polyl-lysine (100 % homology), a natural antimicrobial cationic peptide [52] We found only in BCCO 10_0061 T and BCCO 10_0798 T a BGC for isorenieratene (85 % homology), which is a carotenoid and photooxidation quencher [53]; and a BGC for 2-methylisoborneol (50 % homology), which is a volatile, interspecies signalling molecule similar to and usually found with geosmin [50].…”

“…Terpenes were the most abundant type of BGCs with two clusters for geosmin (100 % homology) [ 48 49 ], being present in all strains. Geosmin is a volatile, earthy-smelling, interspecies signalling molecule [ 48 49 ] that seems to have a very important role in spore dispersion of Streptomyces species [ 50 ].…”

The biosynthesis of the odorant 2-methylisoborneol is compartmentalized inside a protein shell

“…Two of the most prevalent bacterial terpenoids are the methylated monoterpenoid 2-methylisoborneol (2-MIB) and the sesquiterpenoid geosmin, volatile odiferous compounds responsible for the earthy smell of soil and musty taste of contaminated water 2,[6][7][8] . While the exact biological function of these volatile terpenoids is unclear, roles as insect attractants for bacterial spore dispersal 9 and repellants against bacterial predators [10][11][12] have recently been suggested. 2-MIB is widely produced by soil-dwelling Actinobacteria, Myxobacteria, and fungi, as well as by Cyanobacteria 2,6-8, [13][14][15][16] .…”