Aims To evaluate the occurrence, the characterization and identity of nodulating bacteria in symbiosis with Mimosa spp. in the ultramafic massif of Barro Alto, Goiás state, Brazil. Methods Nodules from field grown M. somnians and M. claussenii were sampled for bacteria isolation and in situ detection using microscopy. Isolates were characterized for their nodulation capacity on M. pudica and common bean, and their tolerance to Ni in culture medium. Bacteria were also partially identified by their 16S rRNA gene sequences. In addition, recA , gyrB , nodC and nifH genes from five representative isolates were sequenced for phylogenetic studies . Results In situ detection indicated the exclusive presence of Paraburkholderia sp. within the nodules. This identification was confirmed for most of the isolates by the analysis of their 16S rRNA gene sequences. All isolates identified as Paraburkholderia sp. were able to effectively nodulate M. pudica , but those tested in common bean produced ineffective nodules. Inoculation tests showed that these bacteria improved M. pudica growth in the absence of nitrogen. None of the isolates showed Ni tolerance. The concatenated 16S rRNA, recA and gyrB , and the nodC and nifH genes sequences demonstrated that the five selected isolates were closely related to P. atlantica . Conclusions This is the first report of Paraburkholderia present in nodules from Mimosa plants naturally growing in ultramafic soils. These results suggest that this symbiosis may be a factor to be considered as part of programs to restore ultramafic soils in Barro Alto areas degraded by mining activity.