The master chemists known asStreptomyces bacteria have turned a compoundrich with the tangy odor of moist soil into a hitchhiking scam.

This group of bacteria, the inspirationfor streptomycin and other antibiotics, can release a strong, earthy whiff of whatscalled geosmin. Its not just an everyday scent for them. Some bacterial genes thatregulate spore-making also can trigger geosmin production, an internationalresearch team reports April 6 in NatureMicrobiology. When bacteria start making spores, geosmin wafts into thesoil and attracts hungry little arthropods called springtails. They feast onthe bacteria, inadvertently picking up spores that hitchhike to new territory, says Klas Flrdh, a microbiologist atLund University in Sweden.

Geosmin floats off manyenvironmental microbes, including virtually all Streptomyces. People as well as many other animals can detect lowconcentrations of it. For instance, the common Drosophila lab fruit fly dedicates a circuit in its sensory wiringjust to detecting geosmin, which the flies find repellant. That kind of disgustmight help animals avoid microbially contaminated food. Various springtails,however, flock to the smell.

Springtails aboundin soil (SN: 1/19/14). The springpart of their name comes from a prong latched against the body that snaps looseto smack the ground in a crisis, bouncing the springtail up and away fromdanger.

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Scuttling specks ofspringtails showed up in unusual numbers when coauthor Paul Becher set out bitsof Streptomyces bacteria formingspores under shrubbery at the Swedish University of Agricultural Sciences inAlnarp. A springtail can smell the bacterial geosmin, Becher, Flrdh andcolleagues say after testing the antenna sensitivity of a pale, all-female kindpopular in labs, Folsomia candida.

Genetics linked the alluringgeosmin odor to the bacterial phase of making spores. During that phase, a Streptomyces usual thready networkstarts pushing up spore-making structures. Like skyscrapers, says Flrdh witha microbiologists sense of tall. Lab F.candida springtails readily grazed on these micro skyscrapers, and tests confirmedthat spores from the bacteria stuck to the springtail bodies. Spores can alsospread from fecal pellets.

The idea of feasting springtailsthat disperse bacterial spores echoes what scientists already know about thelittle arthropods eating fungi and giving a lift to their spores, even some thatare dangerous to other arthropods, says microbiologist Valeria Agamennone, whowasnt involved in the new research. (She did her dissertation on springtailsbefore joining the Netherlands Organization for Applied Scientific Research inZeist.) Springtails, she says, may share a long and intimate history withbacteria. She and colleagues have even found some penicillin-making genes that couldhave originated in bacteria but now mingle with springtail genes.

The new work on bacterial luresmakes a delightful paper, says Keith Chater, who worked extensively on Streptomyces at the John Innes Center inNorwich, England, before retiring. In along-ago chat with a journalist, Chater off-handedly mused that geosmin frommoisture-loving bacteria might let camels sniff their way to water in a desert.The idea took on a life of its own, he laments after seeing it repeated moredefinitively than he meant it. As a bacterial geneticist, he never testedcamels. At least now, a somewhat similar geosmin-sniffing tale has turned upwith actual data.

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Earthy funk lures tiny creatures to eat and spread bacterial spores - Science News

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