Diversity, Genomics and Symbiotic Characteristics of Sinorhizobia That Nodulate Desmanthus spp. in Northwest Argentina.

Desmanthus spp. are legumes with the ability to associate with diverse α-proteobacteria-a microsymbiont-in order to establish nitrogen-fixing root nodules. A previous investigation from our laboratory revealed that the main bacteria associated with Desmanthus paspalaceus in symbiosis in central Argentina (Province of Santa Fe) were quite diverse and belonged to the genera Rhizobium and Mesorhizobium. To achieve a more extensive view of the local microsymbionts associated with Desmanthus spp., we sampled three different sites in Jujuy and Salta, in northwest Argentina. Matrix-assisted Laser-Desorption-Ionization Time-of-Flight mass spectrometry (MALDI-TOF) typing, 16S-rDNA analysis, and genome sequencing demonstrated that the dominant root-nodule microsymbionts belonged to the genus Sinorhizobium, with some sequenced genomes related to Sinorhizobium mexicanum, Sinorhizobium chiapanecum, and Sinorhizobium psoraleae. An analysis of nodA and nodC markers indicated that, in some of the isolates, horizontal gene transfer appeared to be responsible for the lack of congruence between the phylogenies of the chromosome and of the symbiotic region. These results revealed diverse evolutionary strategies for reaching the current Desmanthus-microsymbiont diversity. What is remarkable beside their observed genetic diversity is that the tolerance profiles of these isolates to abiotic stresses (temperature, salt concentration, pH) were quite coincident with the separation of the sinorhizobia according to place of origin, suggesting possible ecoedaphic adaptations. This observation, together with the higher aerial dry-weight matter that some isolates generated in Desmanthus virgatus cv. Marc when compared to the biomass generated by the commercial strain Sinorhizobium terangae CB3126, distinguish the collected sinorhizobia as constituting valuable germplasm for evaluation in local fields to select for more efficient symbiotic pairs.

Genome sequence of Bradyrhizobium yuanmingense strain P10 130, a highly efficient nitrogen-fixing bacterium that could be used for Desmodium incanum inoculation.

Strain P10 130, an isolated Bradyrhizobium strain from Argentina which promotes the growth of the leguminous plant Desmodium incanum by different mechanisms was previously selected as the best candidate for D. incanum inoculation based on broader selective criteria. A close relationship between this strain and B. yuanmingense was determined by MALDI BioTyper identification and 16S rRNA gene phylogenetic analysis. This study aimed to analyse the genome sequence of B. yuanmingense P10 130 in order to deepen our knowledge regarding its plant growth-promoting traits and to establish its phylogenetic relationship with other species of Bradyrhizobium genus. The genome size of strain P10 130 was estimated to be 7.54 Mb that consisted of 65 contigs. Genome Average Nucleotide Identity (ANI) analysis revealed that B. yuanmingense CCBAU 10071 T was the closest strain to P10 130 with ca. 96% identity. Further analysis of the genome of B. yuanmingense P10 130 identified 20 nod/nol/NOE, 14 nif/18 fix, 5 nap/5 nor genes, which may be potentially involved in nodulation, nitrogen fixation, and denitrification process respectively. Genome sequence of B. yuanmingense P10 130 is a valuable source of information to continue the research of its potential industrial production as a biofertilizer of D. incanum.