Department of Plant Protection Biology, Swedish University of Agricultural Sciences, Alnarp, Sweden.
Department of Molecular Microbiology, John Innes Centre, Norwich Research Park, Norwich, UK.
Nat Microbiol. 2020 Jun;5(6):821-829. doi: 10.1038/s41564-020-0697-x. Epub 2020 Apr 6.
Volatile compounds emitted by bacteria are often sensed by other organisms as odours, but their ecological roles are poorly understood. Well-known examples are the soil-smelling terpenoids geosmin and 2-methylisoborneol (2-MIB), which humans and various animals sense at extremely low concentrations. The conservation of geosmin biosynthesis genes among virtually all species of Streptomyces bacteria (and genes for the biosynthesis of 2-MIB in about 50%), suggests that the volatiles provide a selective advantage for these soil microbes. We show, in the present study, that these volatiles mediate interactions of apparent mutual benefit between streptomycetes and springtails (Collembola). In field experiments, springtails were attracted to odours emitted by Streptomyces colonies. Geosmin and 2-MIB in these odours induce electrophysiological responses in the antennae of the model springtail Folsomia candida, which is also attracted to both compounds. Moreover, the genes for geosmin and 2-MIB synthases are under the direct control of sporulation-specific transcription factors, constraining emission of the odorants to sporulating colonies. F. candida feeds on the Streptomyces colonies and disseminates spores both via faecal pellets and through adherence to its hydrophobic cuticle. The results indicate that geosmin and 2-MIB production is an integral part of the sporulation process, completing the Streptomyces life cycle by facilitating dispersal of spores by soil arthropods.
细菌挥发的化合物通常被其他生物体感知为气味，但它们的生态作用还不太清楚。众所周知的例子是土壤气味萜类化合物土臭素和 2-甲基异莰醇（2-MIB），人类和各种动物都能在极低的浓度下感知到它们。几乎所有链霉菌（约 50%的链霉菌能合成 2-MIB）物种都保留了土臭素生物合成基因，这表明这些挥发性物质为这些土壤微生物提供了选择性优势。在本研究中，我们表明这些挥发物介导了链霉菌和弹尾目（跳虫）之间明显互利的相互作用。在田间实验中，跳虫被链霉菌菌落散发的气味吸引。这些气味中的土臭素和 2-MIB 会在模式跳虫 Folsomia candida 的触角中引起电生理反应，而该化合物也会吸引 F. candida。此外，土臭素和 2-MIB 合成酶的基因受到孢子形成特异性转录因子的直接控制，限制了气味物质的排放到正在形成孢子的菌落。F. candida 以链霉菌菌落为食，并通过粪便颗粒和通过附着在其疏水性表皮上，传播孢子。结果表明，土臭素和 2-MIB 的产生是孢子形成过程的一个组成部分，通过促进土壤节肢动物传播孢子来完成链霉菌的生命周期。
