Gut microbiome composition and cellulolytic bacteria associated with the carpenter bee Xylocopa frontalis

Carpenter bees of the genus Xylocopa interact extensively with woody substrates during nest construction, suggesting that associated microorganisms may contribute to the degradation of plant-derived polymers. Despite their ecological relevance, the gut microbiome and functional potential of Xylocopa species remain poorly characterized. In this study, we investigated the bacterial and fungal gut microbiome of Xylocopa frontalis using 16S rRNA and ITS amplicon sequencing, complemented by culture-dependent approaches. The gut microbiome was dominated by bacterial taxa commonly associated with bees, including Bombiscardovia, Bifidobacterium, and Frischella, whereas fungal communities were more variable and included genera such as Aspergillus and Cladosporium. Several taxa were consistently detected across samples, indicating recurrent community members; however, a consistent core microbiome was not clearly observed. We established a collection of cultivable microorganisms, including a bacterial isolate capable of utilizing cellulose as a carbon source, as demonstrated by plate assays. Phylogenetic and genomic analyses identified this isolate as Bacillus velezensis strain Xf, which harbors genes associated with cellulose and hemicellulose degradation. These findings suggest the potential for lignocellulose-related metabolism in the gut microbiome. Together, our results provide a combined culture-independent and culture-dependent characterization of the X. frontalis gut microbiome and identify microorganisms with relevant functional traits. Although based on a limited sample size, this study expands current knowledge of microbial associations in carpenter bees and establishes a foundation for future investigations into their functional roles. KEY POINTS: • Gut microbiome of Xylocopa frontalis was characterized by amplicon sequencing • Bacillus velezensis strain Xf showed cellulolytic activity in vitro • Gut-associated microbes showed genes linked to lignocellulose degradation.