Genetic and symbiotic characterization of nitrogen-fixing bacteria from three forest legumes

Abstract

Environmental degradation is a global problem that is closely linked to nature resource misuse, which promotes imbalance of the conditions necessary for natural recovery. In this way it is necessary that there is human intervention in the recovery of these areas. The use of biological nitrogen fixation can improve the quality of recovery projects in degraded areas, favoring the availability of atmospheric nitrogen for forest seedlings, making them more sustainable and less costly, besides generating different benefits in relation to the best establishment of the seedlings in the field. For this it is necessary to identify specific strains for each plant species and with proven efficiency. For this purpose, a study was carried out to identify strains isolated from nodules present in forest seedlings native to the southeastern region of Brazil, Machaerium nyctitans, Platypodium elegans and Ormosia arborea, which would be used to recover areas. The identification of the same was done by sequencing the housekeeping genes (atpD and gyrB) and phylogenetic comparison with sequences of the 16S rRNA gene, in addition, the authentification of these strains in the native forest species and the amplification of the symbiotic nifH gene were performed. In the authentication experiments the nodulation capacity and other morphophysiological parameters (dry mass of the plants, number of nodules, dry mass of nodules, nitrogen content and total amount of N in shoot and SPAD index) of the plants were evaluated to verify the efficiency symbiotic relationship. The phylogenetic analysis of the housekeeping genes showed the presence of new five new clades from the studied strains identified as belonging to the genera Rhizobium (3), Bradyrhizobium (2), which have a high probability of being species not yet described. Among the 21 strains studied, 17 had nodule capacity and in 12 of these it was possible to amplify the symbiotic nifH gene. Among the morphophysiological parameters evaluated, the SPAD index allows to detect a difference in the symbiotic efficiency among the treatments, which was not observed by evaluating the dry mass of the aerial part, correlating the total nitrogen values of the plants.