Female accessory reproductive glands of Paederus fuscipes serve as a reservoir of symbiotic pederin-producing bacteria.

Paederus fuscipes, an ecologically and medically important species, is known for its blistering toxin pederin in hemolymph. Evidence demonstrates that the toxin is synthesized by the uncultured symbiotic pederin-producing bacteria (PPB) in P. fuscipes, but the biological characteristics of PPB within the beetle host remain poorly characterized. Here, we investigated PPB abundance variations in P. fuscipes across different factors (sexes, life stages, habitats, and organs), along with their colonization sites and metabolic potentials. The findings revealed that the PPB abundance in female P. fuscipes at the level of individuals and tissues exhibited stable colonization patterns, independent of habitat and time changes. Notably, PPB dominated the bacterial community in females (relative abundance ≥66.08 %) and nearly occupied reproductive organs (relative abundance ≥96.31 %). Moreover, our results indicated that PPB were predominantly enriched in the accessory glands of female reproductive organs, which could serve as a reservoir for PPB proliferation. Although PPB were not cultured in this study, metagenomic binning yielded the draft genome of PPB (CheckM completeness = 85.14 %, contamination = 0), in which genes related to pederin biosynthesis were identified. Phylogenetic analyses revealed that PPB formed a sister clade to Pseudomonas aeruginosa rather than nesting within the P. aeruginosa lineage. Metabolic module prediction analysis revealed specific deficiencies in PPB's energy metabolism and amino acid biosynthesis pathways, suggesting limited free-living potential for PPB. Collectively, this study provides insights into PPB biological characteristics within their beetle host and paves the way for biotechnological exploitation related to pederin production.