Cobalamin and other corrinoids are essential cofactors for many organisms. The majority of microbes with corrinoid-dependent enzymes do not produce corrinoidsde novo, and instead must acquire corrinoids produced by other organisms in their environment. However, the profile of corrinoids produced in corrinoid-dependent microbial communities, as well as the exchange and modification of corrinoids among community members have not been well studied. In this study, we applied a newly developed liquid chromatography tandem mass spectrometry-based corrinoid detection method to examine relationships among corrinoids, their lower ligand bases and specific microbial groups in microbial communities containingDehalococcoides mccartyithat has an obligate requirement for benzimidazole-containing corrinoids for trichloroethene respiration. We found thatp-cresolylcobamide ([p-Cre]Cba) and cobalamin were the most abundant corrinoids in the communities. It suggests that members of the familyVeillonellaceaeare associated with the production of [p-Cre]Cba. The decrease of supernatant-associated [p-Cre]Cba and the increase of biomass-associated cobalamin were correlated with the growth ofD. mccartyiby dechlorination. This supports the hypothesis thatD. mccartyiis capable of fulfilling its corrinoid requirements in a community through corrinoid remodelling, in this case, by importing extracellular [p-Cre]Cba and 5,6-dimethylbenzimidazole (DMB) (the lower ligand of cobalamin), to produce cobalamin as a cofactor for dechlorination. This study also highlights the role of DMB, the lower ligand produced in all of the studied communities, in corrinoid remodelling. These findings provide novel insights on roles played by different phylogenetic groups in corrinoid production and corrinoid exchange within microbial communities. This study may also have implications for optimizing chlorinated solvent bioremediation.