• The pleasant smell of wet soil indicates

    From ScienceDaily@1:317/3 to All on Tue Apr 5 22:30:38 2022
    The pleasant smell of wet soil indicates danger to bacteria-eating
    worms, researchers find
    The chemical compound geosmin's powerful taste warns predators to keep
    away from certain microbes

    Date:
    April 5, 2022
    Source:
    Concordia University
    Summary:
    Researchers have found that geosmin is made by certain kinds of
    bacteria that are known toxin producers. This acts as a warning to
    C. elegans, a common type of worm, that the bacteria they are about
    to graze on is poisonous. The chemical is an aposematic signal that
    triggers the blind worm's sense of taste just like a caterpillar's
    bright colors or a pufferfish's spines tell a sighted predator to
    stay away.



    FULL STORY ==========================================================================
    The smell of geosmin is unmistakable: it's the odour that permeates the
    air after a summer rain squall or fills your nose while gardening. It's
    the smell of wet soil -- an earthy, almost comforting scent.


    ==========================================================================
    But as a new study just published in the journal Applied and Environmental Microbiology points out, that smell also has a particular purpose. It is
    made by certain kinds of bacteria that are known toxin producers. This
    acts as a warning to C. elegans, a common type of worm, that the
    bacteria they are about to graze on is poisonous. The chemical is an
    aposematic signal that triggers the blind worm's sense of taste just
    like a caterpillar's bright colours or a pufferfish's spines tell a
    sighted predator to stay away.

    Just a few millimetres long, nematodes like C. elegans are tiny but
    found all over the Earth, including Antarctica. Nematodes are also the
    most abundant animal on Earth, accounting for about four-fifths of the
    global animal population. Researchers often use C. elegans as a model
    organism in their studies because their biological systems are less
    complex but similar to those of humans.

    "Through our study, we found that geosmin in Streptomyces coelicolor,
    a bacteria that is toxic to C. elegans, does not appear to have any role
    other than as a signal," says Brandon Findlay, associate professor in
    the Department of Chemistry and Biochemistry and the paper's supervising author. "It doesn't help the cells grow, eat or divide. It doesn't ward
    off predators directly. It just seems to be there as a warning." He
    says he is unaware of any other bacteria-produced chemicals that act in
    that fashion.

    The study was led by Liana Zaroubi (MSc 21), one of Findlay's students
    who is now pursuing her PhD at Simon Fraser University.

    A scent of danger Zaroubi acknowledges that it took her some time to
    arrive at the idea that geosmin was aposematic.



    ==========================================================================
    "It was definitely not obvious," she says. "I eliminated many hypotheses
    before finding that geosmin acted as a warning signal. However, each
    ruled-out experiment revealed important clues that helped elucidate the
    mystery that is geosmin. We followed the science and I believe that
    was key to this discovery." The researchers used several strains of
    C. elegansto test their hypothesis.

    First, they observed the movement and behaviour of worms on agar plates
    where geosmin was present but bacteria was absent. In this instance, the
    worms reacted adversely to the presence of the compound, moving rapidly
    with frequent changes in direction. However, mutant nematodes without
    the chemosensory ASE neuron, which is dedicated to taste, were observed
    to behave normally. Geosmin itself appeared to be non-toxic to C. elegans.

    A separate experiment was designed that included Streptomyces coelicolorbacteria. The researchers observed the worms avoiding their
    prey when they could taste the presence of geosmin. But those without
    the ASE neurons devoured the toxic bacteria, with predictably fatal consequences for both predator and prey.

    A taste of evolution Geosmin is a very pungent compound, detectable by
    humans at five parts per trillion. While many find its odour pleasant,
    it is also a common bacteria- created contaminant in human drinking
    water that can cause water to taste like dirt.

    The extent of geosmin's biological uses is still not completely
    understood.

    However, the researchers believe the compound offers insight into how
    bacteria and their predators interact and how complex behaviours like
    toxin avoidance evolve.

    Along with Zaroubi and Findlay, PhD student Imge Ozugergin, Karina
    Mastronardi (PhD 21), PhD candidate Anic Imfeld, Chris Law at the Centre
    for Microscopy and Cellular Imaging, professor Yves Ge'linas from the Department of Chemistry and Biochemistry and associate professor Alisa
    Piekny from the Department of Biology contributed to the study.


    ========================================================================== Story Source: Materials provided by Concordia_University. Original written
    by Patrick Lejtenyi. Note: Content may be edited for style and length.


    ========================================================================== Journal Reference:
    1. Liana Zaroubi, Imge Ozugergin, Karina Mastronardi, Anic Imfeld,
    Chris
    Law, Yves Ge'linas, Alisa Piekny, Brandon L. Findlay. The Ubiquitous
    Soil Terpene Geosmin Acts as a Warning Chemical. Applied and
    Environmental Microbiology, 2022; DOI: 10.1128/aem.00093-22 ==========================================================================

    Link to news story: https://www.sciencedaily.com/releases/2022/04/220405143530.htm

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