The Putative Involvement of Bacterial Symbionts in Cantharidin Biogenesis: An Explorative Study in Meloidae Insects

Area of Science:

• Insect-microbial interactions
• Chemical ecology
• Microbial biosynthesis

Background:

• Insect-microbe holobionts integrate host and microbial functions, with symbionts aiding nutrition, immunity, and defense.
• Cantharidin, a toxic terpene produced by blister beetles (Coleoptera: Meloidae), possesses defensive and pharmacological properties.
• Males produce and transfer cantharidin to females during mating.

Purpose of the Study:

• To investigate the potential involvement of insect-associated bacteria in the biosynthesis of cantharidin.
• To assess the antibacterial activity of cantharidin against representative bacterial strains.
• To analyze the microbiome composition in relation to sex in cantharidin-producing blister beetles.

Main Methods:

• Antibacterial susceptibility testing of six reference bacterial strains against cantharidin.
• 16S rRNA gene sequencing (V5-V6 region) for metataxonomic profiling of insect-associated microbiomes.
• Comparative microbiome analysis between male and female blister beetles from five cantharidin-producing species.

Main Results:

• All tested bacterial strains tolerated cantharidin up to 600 µg/ml, indicating intrinsic resistance.
• Microbiomes were dominated by Pseudomonadota, with secondary contributions from Actinomycetota and Cyanobacteriota.
• While overall microbiome structure did not differ significantly between sexes, certain taxa (Staphylococcus, Cutibacterium, Enterobacteriaceae) were more abundant in males.

Conclusions:

• The intrinsic resistance of bacteria to cantharidin and sex-specific microbiome differences support the hypothesis of bacterial involvement in cantharidin biogenesis.
• Further research is warranted to elucidate the specific bacterial taxa and metabolic pathways responsible for cantharidin production.