Genetic diversity and salt tolerance of Sinorhizobium populations from two Tunisian soils

Leguminous plants are promising pioneer-species for colonization of marginal areas and soils undergoing desertification. They derive part of their colonization abilities from their symbiotic interaction with nitrogen-fixing bacteria known as rhizobia. In this work, we analyzed total and culturable rhizobium communities from two Tunisian soils in close proximity to each other: one non-salty and cultivated and the other uncultivated and salty. The taxonomic diversity of the Rhizobiaceae family, evaluated by terminal restriction fragment length polymorphism (T-RFLP) on total soil DNA, revealed a high diversity of ribotypes and soil-based differentiation of the communities. We then used PCR-RFLP of the intergenic space and salt tolerance to characterize the genetic and phenotypic polymorphism of 150 Sinorhizobium isolates trapped on Medicago truncatula. In the salty soil, two different species, Sinorhizobium meliloti and Sinorhizobium medicae, were trapped; by contrast, only isolates of S. meliloti were trapped from the agricultural soil. Moreover, isolates from the salty soil were more tolerant to NaCl, and strains growing up to 1 M NaCl were found. No relationships between genotypic profiles and salt tolerance phenotypes were found.