Bacteria responsible for fishy smell

Biosynthesis of methylisoborneol decodes

An agar plate fully covered with a bacterium of the genus Streptomyces, which produces methylisoborneol © TU Braunschweig
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Sometimes it smells like fresh earth, sometimes mushy, musty and unpleasant: Methylisoborneol. The substance is sometimes found outside the earth in drinking water and food fish and is produced exclusively by bacteria. Researchers have now demonstrated for the first time how the microorganisms produce the fragrance. They report on the results of their study in the journal Angewandte Chemie.

For humans, methylisoborneol is not harmful. But almost everyone feels the smell in connection with drinking water as extremely unpleasant and deterrent. Even fresh water is considered inedible as soon as the substance is perceived in it. Even in the slightest concentration of only ten nanograms per liter, it is sniffed by our noses.

Water companies therefore remove methyl isoborneol in drinking water treatment at great expense. Also in fish, the volatile substance can accumulate, which are then considered inedible due to the typical "mud aroma". Professor Stefan Schulz from the Institute of Organic Chemistry at the Technical University of Braunschweig has developed a hypothesis for the unpleasant effect of methyl isoborneol on humans. "Obviously the smell in connection with everything we want to eat and drink scares us off so vehemently because it emits a drastic warning signal. But what sense makes this warning if the substance is harmless in itself? "Asks Schulz.

Odor as a warning signal

"Interestingly, some of the bacteria that also make methylisoborneol also produce highly toxic substances for humans. Cyanobacteria, also called blue-green algae, and found in stagnant water can produce very dangerous toxins, but you can not smell them. In the course of evolution, humans may have learned to interpret the penetrating smell as a warning sign of this danger. ", Says Schulz.

Bacteria produce the typical smell of fresh earth. In drinking water or in food fish, the same aroma has a deterrent effect on people TU Braunschweig

The food industry is therefore particularly interested in research results on methylisoborneol. On the basis of the results that the Institute of Organic Chemistry has worked out together with scientists at the Helmholtz Center for Infection Research in Braunschweig and at the University of Saarbrücken, researchers can now investigate search for the genes responsible for the synthesis of methylisoborneol, and later inhibit, for example, the corresponding production mechanisms in the bacteria involved. display

In search of the meaning of fragrances and flavors

In addition to these applications, chemists are generally interested in the biosynthesis of aromas. "We want to know exactly why bacteria produce odors, " explains Schulz. Who thinks about bacteria, if he enjoys a good cheese and a glass of red wine, if he carries out the stinking Biom ll or on walk just this earthy smell of methylisoborneol in the nose gets? All these smells and flavors are made by bacteria

But what function do they perform in nature and how have the taste and smell receptors in humans adapted to this in the course of evolution? How and why aromas are created has been poorly understood. Schulz's vision is to present a cartography of all the bacteria-produced fragrances and to explore their function in the interaction of the living beings.

(idw - Technical University Braunschweig, 19.11.2007 - DLO)