Characterization of root-nodulating bacteria on Retama raetam in arid Tunisian soils

The aim of this study is to investigate the diversity of Retama raetam root-nodule bacteria isolated from arid regions of Tunisia. Twelve isolates, chosen as representative for different 16S rRNA gene patterns, were characterized by 16S rRNA gene sequencing and phenotypic analysis. Isolates were assigned to Sinorhizobium, Rhizobium and Agrobacterium. Symbiotic properties of Sinorhizobium and Rhizobium isolates showed a large diversity in their capacity to infect their host plant and fix atmospheric nitrogen. Strain RK 22 identified as Rhizobium was the most effective isolate.     

Genetic diversity of rhizobial populations recovered from three Lotus species cultivated in the infra-arid Tunisian soils

Eighty-three bacterial strains isolated from root nodules of Lotus creticus, L. pusillus, and L. arabicus grown in infra-arid Tunisian soils were characterized using a polyphasic approach including phenotypic analysis, rep-PCR and PCR-RFLP analyses of the 16S rRNA gene. Phenotypically, all isolates are fast growers the majority of which grow at a pH of between 5.5 and 9. Most of the tested isolates tolerate NaCl concentrations from 1.39% to 3.48%. By rep-PCR fingerprinting, the genomic similarity varied from 30% to 98%. All tested isolates were clustered into 32 rep-PCR clusters at the similarity level of 80%. The genomic divergence of strains revealed by rep/PCR analysis appeared to be very important since a molecular polymorphism delimiting symbionts for each species of Lotus was identified. With the high-resolution of rep-PCR profiles of the isolates obtained using Pearson’s/UPGMA analysis, the isolates were resolved into 60 different profiling groups to undergo 16S ARDRA analyses. The analysis of all restriction fragments from each strain based on the UPGMA algorithm from the combined patterns showed that Lotus isolates are very diverse and that they were affiliated to Sinorhizobium, Rhizobium, and Mesorhizobium genera.     

Genetic diversity of rhizobial populations recovered from three Lotus species cultivated in the infra-arid Tunisian soils

gments from each strain based on the UPGMA algorithm from the combined patterns showed that Lotus isolates are very diverse and that they were affiliated to Sinorhizobium,Rhizobium,and Mesorhizobium genera.