Ketalization of 2-heptanone to prolong its activity as mite repellant for the protection of honey bees

Biosynthesis of 2-Heptanone, a Volatile Organic Compound with a Protective Role against Honey Bee Pathogens, by Hive Associated Bacteria

Beehives are populated by bacterial species with a protective role against honey bee pathogens thanks to the production of bioactive metabolites. These compounds are largely unexploited despite their high potential interest for pest management. This study evaluated the capability of bacterial species associated with honey bees to produce 2-heptanone, a volatile organic compound with anesthetic properties of the parasitic mite Varroa destructor. The production of this compound was quantified by SPME-GC-MS in a culture filtrate of nine bacterial strains isolated from the surface of honey bees, and the biosynthetic potential was evaluated in bacterial species associated with apiaries by searching for protein homologs putatively involved in its biosynthesis by using biocomputational tools. The findings pointed out that 2-heptanone was produced by Acetobacteraceae bacterium, Bacillus thuringiensis and Apilactobacillus kunkeei isolates in concentrations between 1.5 and 2.6 ng/mL and that its production was strain-specific. Putative methylketone synthase homologs were found in Bacillus, Gilliamella, Acetobacteraceae, Bartonella and Lactobacillaceae, and the protein sequence results were distributed in nine Sequence Similarity Network (SSN) clusters. These preliminary results support the hypothesis that 2-heptanone may act as a mediator of microbial relationships in hives and provide contributions to assess the role and biosynthetic potential of 2-heptanone in apiaries.

Honey bee-associated bacteria as producers of bioactive compounds for protecting hives. A biosynthetic gene-based approach

Honey bee-associated bacteria are a source of natural compounds of interest for controlling hive decline which is threatening bee health globally. Genes involved in the biosynthesis of a series of extracellular compounds released by bacteria living on the external surface of honey bees were investigated. A biosynthetic gene-based approach was adopted by developing a battery of primers to target the genes involved in the biosynthesis of four groups of bioactive compounds (pyrrolizidine alkaloids, surfactin, 2-heptanone and helveticin J). The primers were tested on 51 bacterial isolates belonging to Bacillus thuringiensis, Acetobacteraceae bacterium, Bifidobacterium asteroides and Apilactobacillus kunkeei. The developed primers led to species-specific detection and characterization of the functional genes involved in the production of three out of four groups of compounds selected for this study. The findings suggest that microbial populations inhabiting apiaries harbor genes involved in the biosynthesis of metabolites linked to the reduction of important honey bee pathogens such as Varroa destructor, Paenibacillus larvae and Nosema ceranae. The gene-based approach adopted for evaluating the biosynthetic potential of bioactive compounds in hives is promising for investigating further compounds for low input control strategies of bee enemies.