Permanent draft genome sequence of Bradyrhizobium vignae, strain ISRA 400, an elite nitrogen-fixing bacterium, isolated from the groundnut growing area in Senegal.

A new Bradyrhizobium vignae strain called ISRA400 was isolated from groundnut (Arachis hypogaea L.) root nodules obtained by trapping the bacteria from soil samples collected in the Senegalese groundnut basin. In this study, we present the draft genome sequence of this strain ISRA400, which spans approximatively 7.9 Mbp and exhibits a G+C content of 63.4%. The genome analysis revealed the presence of 48 tRNA genes and one rRNA operon (16S, 23S, and 5S). The nodulation test revealed that this strain ISRA400 significantly improves the nodulation parameters and chlorophyll content of the Arachis hypogaea variety Fleur11. These findings suggest the potential of Bradyrhizobium vignae strain ISRA400 as an effective symbiotic partner for improving the growth and productivity of groundnut crop.

Development of an Illumina-based analysis method to study bradyrhizobial population structure-case study on nitrogen-fixing rhizobia associating with cowpea or peanut.

Bradyrhizobia are Gram-negative soil bacteria that regroup a growing number of species. They are widespread in nature and recovered from various biomes that may be explained by a high genetic diversity in this genus. Among the numerous metabolic properties they can harbor, the nitrogen fixation resulting from the association with plants among which important crop legumes (soya bean, peanut, cowpea …) is of great interest, notably in a context of sustainable development. Metabarcoding is widely applied to study biodiversity from complex microbial communities. Here, we demonstrate that using a new species-specific and highly polymorphic 16S-23S rRNA intergenic spacer barcode, we could rapidly estimate the diversity of bradyrhizobial populations that associate with cowpea and peanut plants, two crop legumes of major interest in Senegal. Application of the method on indigenous bradyrhizobia associated with peanut and cowpea grown in soils collected in the center of the peanut basin shows that Bradyrhizobium vignae is a dominant symbiont. We also showed that the two plant species associate with distinct community profiles and that strains introduced by inoculation significantly modified the population structure with these two plants suggesting that application of elite strains as inoculants may well ensure optimized symbiotic performance. This approach may further be used to study the diversity of bradyrhizobia from contrasting agro-eco-climatic zones, to test whether the plant genotype influences the association outputs as well as to estimate the competitiveness for nodule occupancy and the fate of elite strains inoculated in the field.Key points• An amplicon sequencing approach targeting the Bradyrhizobium genus was developed.• Diversity of cowpea and peanut bradyrhizobia from cultivated soils was identified.• The method is well suited to test the competitiveness of defined Bradyrhizobium inoculants.