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Applied and Environmental Microbiology, September 2008, p. 5653-5661, Vol. 74, No. 18
0099-2240/08/$08.00+0     doi:10.1128/AEM.01107-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Effects of Medicago truncatula Genetic Diversity, Rhizobial Competition, and Strain Effectiveness on the Diversity of a Natural Sinorhizobium Species Community{triangledown}

Cécile Rangin,1,5* Brigitte Brunel,2 Jean-Claude Cleyet-Marel,3 Marie-Mathilde Perrineau,4 and Gilles Béna1

IRD, UMR 113, Laboratoire des Symbioses Tropicales et Méditerranéennes, Campus International de Baillarguet TA A-82/J, F-34398 Montpellier Cedex 5, France,1 Montpellier SupAgro, UMR 113, Laboratoire des Symbioses Tropicales et Méditerranéennes, Campus International de Baillarguet TA A-82/J, F-34398 Montpellier Cedex 5, France,2 INRA, USC1242, Laboratoire des Symbioses Tropicales et Méditerranéennes, Campus International de Baillarguet TA A-82/J, F-34398 Montpellier Cedex 5, France,3 CIRAD, UMR 113, Laboratoire des Symbioses Tropicales et Méditerranéennes, Campus International de Baillarguet TA A-82/J, F-34398 Montpellier Cedex 5, France,4 Université Montpellier II, UMR 113, Laboratoire des Symbioses Tropicales et Méditerranéennes, Campus International de Baillarguet TA A-82/J, F-34398 Montpellier Cedex 5, France5

Received 16 May 2008/ Accepted 14 July 2008

We investigated the genetic diversity and symbiotic efficiency of 223 Sinorhizobium sp. isolates sampled from a single Mediterranean soil and trapped with four Medicago truncatula lines. DNA molecular polymorphism was estimated by capillary electrophoresis-single-stranded conformation polymorphism and restriction fragment length polymorphism on five loci (IGSNOD, typA, virB11, avhB11, and the 16S rRNA gene). More than 90% of the rhizobia isolated belonged to the Sinorhizobium medicae species (others belonged to Sinorhizobium meliloti), with different proportions of the two species among the four M. truncatula lines. The S. meliloti population was more diverse than that of S. medicae, and significant genetic differentiation among bacterial populations was detected. Single inoculations performed in tubes with each bacterial genotype and each plant line showed significant bacterium-plant line interactions for nodulation and N2 fixation levels. Competition experiments within each species highlighted either strong or weak competition among genotypes within S. medicae and S. meliloti, respectively. Interspecies competition experiments showed S. meliloti to be more competitive than S. medicae for nodulation. Although not highly divergent at a nucleotide level, isolates collected from this single soil sample displayed wide polymorphism for both nodulation and N2 fixation. Each M. truncatula line might influence Sinorhizobium soil population diversity differently via its symbiotic preferences. Our data suggested that the two species did not evolve similarly, with S. meliloti showing polymorphism and variable selective pressures and S. medicae showing traces of a recent demographic expansion. Strain effectiveness might have played a role in the species and genotype proportions, but in conjunction with strain adaptation to environmental factors.

* Corresponding author. Mailing address: IRD, UMR 113, Laboratoire des Symbioses Tropicales et Méditerranéennes, Campus International de Baillarguet TA A-82/J, F-34398 Montpellier Cedex 5, France. Phone: (33) 4 67 59 38 01. Fax: (33) 4 67 59 38 02. E-mail: rangin{at}mpl.ird.fr

{triangledown} Published ahead of print on 25 July 2008.

Applied and Environmental Microbiology, September 2008, p. 5653-5661, Vol. 74, No. 18
0099-2240/08/$08.00+0     doi:10.1128/AEM.01107-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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