Species belonging to the genusRahnellaare dominant members of the core gut bacteriome ofDendroctonus-bark beetles, a group of insects that includes the most destructive agents of pine forest in North and Central America, and Eurasia. From 300 isolates recovered from the gut of these beetles, 10 were selected to describe an ecotype ofRahnella contaminans. The polyphasic approach conducted with these isolates included phenotypic characteristics, fatty acid analysis, 16S rRNA gene, multilocus sequence analyses (gyrB,rpoB,infB,andatpDgenes), and complete genome sequencing of two isolates, ChDrAdgB13 and JaDmexAd06, representative of the studied set. Phenotypic characterization, chemotaxonomic analysis, phylogenetic analyses of the 16S rRNA gene, and multilocus sequence analysis showed that these isolates belonged toRahnella contaminans. The G + C content of the genome of ChDrAdgB13 (52.8%) and JaDmexAd06 (52.9%) was similar to those from otherRahnellaspecies. The ANI between ChdrAdgB13 and JaDmexAd06 andRahnellaspecies includingR. contaminans, varied from 84.02 to 99.18%. The phylogenomic analysis showed that both strains integrated a consistent and well-defined cluster, together withR. contaminans. A noteworthy observation is the presence of peritrichous flagella and fimbriae in the strains ChDrAdgB13 and JaDmexAd06. Thein silicoanalysis of genes encoding the flagellar system of these strains andRahnellaspecies showed the presence offlag-1 primary system encoding peritrichous flagella, as well as fimbriae genes from the families type 1, α, β and σ mainly encoding chaperone/usher fimbriae and other uncharacterized families. All this evidence indicates that isolates from the gut ofDendroctonus-bark beetles are an ecotype ofR. contaminans, which is dominant and persistent in all developmental stages of these bark beetles and one of the main members of their core gut bacteriome.