Nitrogen is a limited resource for many organisms. In particular, Dendroctonus (Coleoptera: Scolytinae) bark beetles feed on pine cambium and phloem, a nitrogen poor substrate. Dendroctonus valens is a bark beetle widely distributed in pine forests. In this work entire adults and larvae of D. valens collected from infected trees were able of acetylene reduction, an assay to indirectly measure the molecular nitrogen fixation. On other hand, the bacterial community, the nitrogen-fixing bacteria and relevant nitrogen cycle genes were detected in Dendroctonus gut. Thus metagenomic DNA and bacterial cultures were obtained and nifH, nifD y amoA genes were amplified by PCR. The bacterial community of the D. valens gut was restricted to Acinetobacter sp., Rahnella aquatilis, Serratia sp., Enterobacter sp., Pantoea sp., Stenotrophomonas maltophilia and actinobacteria members, species or genera that previously have been reported as symbiotic bacteria of the digestive tract of several insects. Particularly, R. aquatilis, Pantoea sp. and S. maltophilia were able to grow in media without nitrogen source, but no nitrogen fixing was detected in vitro. Basically, no differences in the total gut bacterial community among the gut sections, sexes, and insects from different localities were observed by DGGE analysis. Finally, genes implied in nitrogen fixation were detected in gut metagenomic DNA, although no amplification was obtained from isolated bacteria DNA. Evidently, bark beetles bacterial community maintains active nitrogen fixing bacteria that introduce an additional assimilable nitrogen source to insect diet.