D3453: Casting light on microbial symbioses of fireflies

Fireflies (Lampyridae) are iconic insects due to their bioluminescence, but are threatened worldwide. Despite the urgent need to understand their biology to better conserve them, it remains unclear whether fireflies harbor a stable microbiome. Potential benefits provided by microbial symbionts have never been evaluated in this insect clade. Yet, bioluminescent fireflies require precursors of key enzymatic substrates and energy supplies to fuel light emission. Bacterial symbionts could participate in such demanding tasks. Previous studies show that Mollicutes bacteria are common associates of these insects. We thus hypothesized that many firefly species partner with conserved, specialized Mollicutes, that have been domesticated by a lampyrid ancestor, and that provide benefits to firefly hosts. In a pilot study, we characterized the microbiome of 19 firefly specimens (6 species from 3 genera) using 16S rRNA amplicon sequencing and analyzed the evolution and functions encoded in 7 firefly-isolated Mollicutes genomes. We show that bacterial community profiles differ across firefly genera. Two variants from the Williamsoniiplasma genus (Mollicutes) are prevalent and abundant in common bioluminescent Lampyrinae species (Photinus pyralis and Pyractomena borealis). Firefly-associated Williamsoniiplasma have conserved the genomic ability to produce hydroquinone, a precursor of luciferin, which is the substrate of bioluminescence. Building upon these preliminary results, we intend to conduct a more comprehensive microbiome survey across firefly clades and sequence new firefly-isolated bacterial genomes. Through this research, we will infer the stability of bacterial associations in fireflies, ascertain firefly dependency upon microbial symbionts and evaluate the role such partners play in firefly biology.