Secondary Metabolites Produced by Honey Bee-Associated Bacteria for Apiary Health: Potential Activity of Platynecine
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Secondary Metabolites Produced by Honey Bee‑Associated Bacteria for Apiary Health: Potential Activity of Platynecine L. M. Manici1,2 · M. L. Saccà1 · M. Lodesani1 Received: 19 March 2020 / Accepted: 28 July 2020 © Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Secondary metabolites of bacteria associated with honey bees were evaluated as part of an investigation on their potentiality for apiary health. Low molecular weight compounds released into culture filtrates by the four bacterial isolates taken from surface of healthy honey bees were analyzed using time-of-flight mass spectrometry. Only one low molecular weight compound was found in the culture filtrate of each isolate. Bacillus thuringiensis, Bifidobacterium asteroides and Acetobacteraceae bacterium, released into culture filtrates platynecine, a pyrrolizidine alkaloid of plant origin, which, until now, had never been reported as produced by bacteria. Lactobacillus kunkeei produced a 3,5-dinitropyridine, of unknown biological action never associated so far to bacteria. The highest relative concentration of platynecine was detected in B. thuringiensis (100%), B. asteroides and A. bacterium showed a concentration above 50% and below 25% that concentration. An in vitro assay on the potential for controlling the parasitic mite Varroa destructor by the culture filtrates of the three platynecineproducing bacteria was performed. Varroa mite mortality was proportional to the platynecine relative concentration into culture filtrate. Although miticidal activity of B. thuringiensis might be associated to other toxic proteins produced by this species, B. asteroides toxicity toward V. destructor along with the other findings of this study support the hypothesis that platynecine plays a direct or an indirect role in controlling varroa. Findings of this study suggest that secondary metabolites released by honey bee-associated bacteria represent a source of natural compounds to be considered in the challenge for counteracting the colony decline.
Introduction Honey bee (Apis mellifera, Apidae) is a managed wildlife species representing a key natural resource for its pollination work in a variety of ecosystems, both wild and agricultural, as well as for honey and wax production. Overall the global number of colonies has increased by 45% since 1961; in the mid-1980s, however, long-term declines and annual losses began in honey bee colonies throughout Europe and the U.S. Colony losses accounted for 25% at the beginning rising to 60% in around 2010 [1, 2]. This decline has multiple causes an increasing use of pesticides, changed environmental and socio-economic factors, a series of endemic and new
* L. M. Manici [email protected] 1
Council for Agricultural Research and Economics (CREA), Research Center for Agriculture and Environment, Via di Corticella 133, 40128 Bologna, Italy
CREA-AA, via di Corticella 133, Bologna, Italy
2
diseases threatening honey bees along with alien parasites are the main causes [3]. One of the most
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