First Shotgun Metagenomic Characterization of the Gut Microbiome of the Endangered Longhorn Beetle Callipogon relictus (Coleoptera: Cerambycidae)

The gut microbiome of Callipogon relictus, a rare member of the family Cerambycidae, was characterized for the first time using shotgun metagenomic sequencing. The aim of this study was to compare the taxonomic diversity and structure of the gut microbial communities in larvae and adults. Bacteria dominated the metagenomic profiles, accounting for 92.47% of the taxonomic composition in adults and 85.31% in larvae. Proteobacteria predominated in the bacterial component of both pooled profiles, accounting for 87.88% and 89.43%, respectively. The pooled adult profile had the highest relative abundances of Gammaproteobacteria and Enterobacterales, whereas the pooled larval profile had higher relative abundances of Alphaproteobacteria and Rickettsiales. In the pooled samples analyzed, 155 bacterial and 69 fungal genera were detected in the larval profile, compared with 85 and 17 genera, respectively, in the adult profile; the fungal component accounted for 10.46% of the larval profile and 0.18% of the adult profile. The two profiles shared 77 bacterial, 17 fungal, and 15 protist genera. The virus-like/retroelement sequence fraction was dominated by sequences related to Errantivirus, a member of the family Metaviridae. Because Metaviridae comprise LTR retrotransposons, this signal was interpreted as endogenous retroelement DNA rather than evidence of a free-virus gut virome. These results provide a preliminary description of a shared bacterial core accompanied by differences between the pooled profiles in lower-rank bacterial composition and in the structure of the fungal and protist components of the C. relictus microbiome.