Nitrogen-fixing Rhizobium bacteria in nodules on the roots of leguminous forest trees are an
important means of maintaining such plants in nutrient-poor tropical soils. These bacteria are
used in agroflorestry systems to recover the fertility and sustainability of degraded soils. This
study aimed to characterize 28 isolates of rhizobia isolated from petroleum residues
contaminated soils according to its phenotipic diversity and nitrogen fixation potential. The
isolates were phenotipically characterized in yeast-mannitol minimal medium supplemented
with 8 different carbon sources and the data was analysed through numerical cluster analysis,
comparing with strains belonging to the bacterial species which nodulate legume trees. At a
similarity of 69,5% most isolates formed great groups with Rhizobium, Sinorhizobium and
Burkholderia . A second grouping with 4 isolates was formed at a similarity of 70% with the
bacteria Cupriavidus taiwanensis and Azorhizobium doebereinerae. The isolate L79 presented
similarity of 95% with the bacteria Azorhizobium doebereinerae. The efficiency of selected
isolates was tested in experiments arranged in factorial randomized block design with three
replicates. Treatments consisted of 13 selected isolates and three control treatments: (1) plants
inoculated with the commercial isolates; (2) plants grown without nitrogen and non inoculated
and (3) nitrogen supplied plants. Quantitative results were analyzed by statistic software
SISVAR. The analyzed variable was shoot dry weight and nodule weight to calculate the
efficiency of the isolates. All the three legume tree presented statistical difference about shoot
and nodule dry weight. Six isolates showed higher efficiency than commercial recommend
strains to be inoculated in two species of legume trees (Mimosa caesalpinaeifolia Benth and
Albizia saman (Jacq.) Merr).
