Symbiotic efficiency in Vigna unguiculata and Mimosa bimucronata and genetic characterization of Bradyrhizobium and Paraburkholderia strains originating from soils of the Quadrilátero Ferrífero

Abstract

Nitrogen (N) has notable importance within ecosystems. In general, this element is inaccessible to most organisms, being used by bacterial species, known as diazotrophs. The process of biological nitrogen fixation (BNF) can occur through symbiosis between legumes and rhizobia and represents a clean and economical source of N, as it can reduce possible environmental impacts caused by the use of fertilizers and production costs by partial or total of these fertilizers. Therefore, identifying the bacteria present in soils and their ability to promote plant growth is the first step towards selecting species with potential for use as leguminous inoculants and also towards the development of strategies aimed at improving the management and recovery of degraded areas. Several strains of diazotrophs were isolated from soils of different phytophysiognomies of the Iron Quadrangle using Vigna unguiculata as a bait plant, among which strains of the genera Bradyrhizobium and Paraburkholderia stood out. Iron Quadrangle of Minas Gerais of the genera Bradyrhizobium (23) and Paraburkholderia (46), regarding their efficiency in promoting growth and nodularity respectively Vigna unguiculata and Mimosa bimucronata; (2) Verify the positioning of the strains under study in relation to the type species already described based on partial sequences of the 16S rRNA gene and genome sequencing of representative strains of groups obtained by partial sequences of the 16S rRNA gene; (3) Identify possible new species among the analyzed strains. Initially, experiments were implemented in a greenhouse, inoculating the strains in plants of Mimosa bimucronata and Vigna unguiculata. Subsequently, the chlorophyll content present in the leaves of the plants and the parameters of symbiotic efficiency and nodulation were evaluated. Phylogenetic trees were built using the partial sequences of the 16S rRNA gene of the type species of each genus and strains under study. Then, the genomic DNA sequencing of representative strains of phylogenetic groups obtained by partial sequences of the 16S rRNA gene that indicated possibly new species was carried out, and the Average Nucleotide Identity (ANI) calculated, for comparison of the genome of the strains analyzed with the genome of the species already described. Most of the Bradyrhizobium strains were efficient on Vigna unguiculata and some of them represent new species. Regarding the Paraburkholderia strains, most were able to nodulate Mimosa bimucronata plants, and the UFLA 03-690 strain stood out for presenting the best results.