Symbiotic efficiency with Enterolobium contortisiliquum, adaptability, and functional genes of Bradyrhizobium strains isolated from soils with high Fe and Mn content

Symbiotic association between leguminous trees and nodulating N 2 -fixing bacteria plays an important role in the process of recovery of degraded areas by mining activities. However, a fundamental condition for success in symbiosis is the use of efficient strains adapted to edaphic and climatic conditions. Besides, there is a need for studies that focus on genes that explain this adaptive capacity. The aim of this study was to evaluate the efficiency and adaptive capacity of Bradyrhizobium strains, originating from iron (Fe) mining areas, in symbiosis with Enterolobium contortisiliquum . Symbiotic efficiency of 39 strains was evaluated in a greenhouse under axenic conditions in comparison with controls without inoculation or inoculation with the strain efficient for the species. After that, 12 strains selected from among the 39 were tested in soil coming from an iron-mining area and compared with the same controls used previously. Four strains were selected based on the trials with soil for the study of genomic DNA. Plants inoculated with the strains selected for genomic DNA sequencing showed high symbiotic efficiency with Enterolobium contortisiliquum and adaptation to the soil both under axenic and soil conditions. Genomic DNA analysis showed the presence of pin5, acdS , sodA , bfr , gshB , and gor , reported in the literature as genes related to tolerance to high Fe and Mn contents, as well as the genes nod C and nif H, related to the symbiosis and N 2 - fixation.