The microbiome of the burying beetle Nicrophorus vespilloides as an untapped source for the screening of bioactive small molecules

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HeisePhilipp_2019_05_23.pdf (9.97 MB)

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2019

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DOI:
http://dx.doi.org/10.22029/jlupub-10472

Abstract

Nicrophorus vespilloides is a native species of burying beetles, the reproduction of which depends on small vertebrate carcasses e.g. those of small rodents. Carrion is buried is buried in the soil in order to reduce competitition with other scavenger insects. However, this behaviour unevitably increases the exposition of the carrion to a broad range of soil-borne microorganisms. Therefore, beetles of the genus Nicrophorus have evolved an efficient strategy for carcass preservation, thus to preserving the carrion as food source for its larvae.It appears, however, that the phenomenon of carcass preservation by burying beetles is one of nature s best kept secrets. A number of pioneering studies have shown that oral and anal secretions of N. vespilloides contain antimicrobial and preserving and repellent molecules. Notably, beetles of the genus Nicrophorus harbour a unique gut flora, which is applied onto the surface of the carcass in order to contribute to its preservation.This study focusses on the cultivation of bacterial isolates originating from the gut flora and the antimicrobial compounds produced by those microbes. Therefore, N. vespilloides caught in the wild as well as laboratory-hatched animals were investigated. Beetles were dissected, their gut was removed, and gut-associated microorganisms were cultivated. Pure cultures obtained by this procedure were identified by 16S rRNA gene analysis.To identify producers of antimicrobial activities, a classical screening for natural products was performed. Approximately 800 extracts were subsequently tested against a broad spectrum of taxonamically defined bacteria and fungi. In the course of this screening, a multitude of antimicrobial activities could be observed.Some isolates of the highly abundant genus Serratia displayed a broad spectrum of antimicrobial activity. A single isolate, which could be identified as Serratia marcescens, effectively inhibbite Staphylococcus aureus. This strain was selected for further detailed studies. The antibiotic activity was isolated and its structure elucidated by NMR spectroscopy. Finally, the antibiotic principle was identified as serrawettin W2. After purification, this cyclic pentadepsipeptide exhibited antimicrobial activity against further Gram-positive bacteria. Serrawettin W2, which has previously been reported as a nematode repellent, was shown to act as a nematostatic agent. The combination of these antimicribial and nematostatic bioactivities could be of importance for the ecology of burying beetles. After burying, the carcass is not only threatened by microorganisms but also by soil-borne nematodes. Consequently, a symbiosis of Nicrophorus sp. with a beneficial gut bacterium is hypothesised to positively contribute to to the preservation of the carcass, which is used for reproduction of the beetles.

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