Archives of Microbiology

, Volume 187, Issue 1, pp 79–85 | Cite as

Salt-tolerant rhizobia isolated from a Tunisian oasis that are highly effective for symbiotic N2-fixation with Phaseolus vulgaris constitute a novel biovar (bv. mediterranense) of Sinorhizobium meliloti

  • Bacem Mnasri
  • Moncef Mrabet
  • Gisèle Laguerre
  • Mohamed Elarbi Aouani
  • Ridha Mhamdi
Short Communication


Nodulation of common bean was explored in six oases in the south of Tunisia. Nineteen isolates were characterized by PCR–RFLP of 16S rDNA. Three species of rhizobia were identified, Rhizobium etli, Rhizobium gallicum and Sinorhizobium meliloti. The diversity of the symbiotic genes was then assessed by PCR–RFLP of nodC and nifH genes. The majority of the symbiotic genotypes were conserved between oases and other soils of the north of the country. Sinorhizobia isolated from bean were then compared with isolates from Medicago truncatula plants grown in the oases soils. All the nodC types except for nodC type p that was specific to common bean isolates were shared by both hosts. The four isolates with nodC type p induced N2-fixing effective nodules on common bean but did not nodulate M. truncatula and Medicago sativa. The phylogenetic analysis of nifH and nodC genes showed that these isolates carry symbiotic genes different from those previously characterized among Medicago and bean symbionts, but closely related to those of S. fredii Spanish and Tunisian isolates effective in symbiosis with common bean but unable to nodulate soybean. The creation of a novel biovar shared by S. meliloti and S. fredii, bv. mediterranense, was proposed.


Biovar mediterranense Genetic diversity Medicago Phaseolus vulgaris Rhizobia Salt tolerance 



This work was supported in part by grants from Aquarhiz project (509115).


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Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • Bacem Mnasri
    • 1
  • Moncef Mrabet
    • 1
  • Gisèle Laguerre
    • 2
  • Mohamed Elarbi Aouani
    • 1
  • Ridha Mhamdi
    • 1
  1. 1.Laboratoire Interactions Légumineuses-MicroorganismesCentre de Biotechnologie à la Technopole de Borj-CédriaHammam-lifTunisia
  2. 2.UMR Microbiologie et Géochimie des SolsINRA-Université de BourgogneDijonFrance

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