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Applied and Environmental Microbiology, December 2007, p. 7597-7604, Vol. 73, No. 23
0099-2240/07/$08.00+0     doi:10.1128/AEM.01046-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Chromosomal and Symbiotic Relationships of Rhizobia Nodulating Medicago truncatula and M. laciniata{triangledown}

Peter van Berkum,1* Yazid Badri,2 Patrick Elia,1 Mohammed Elarbi Aouani,2 and Bertrand D. Eardly3

Soybean Genomics and Improvement Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Maryland 20705,1 Laboratoire Interactions Légumineuses Microorganismes, Centre de Biotechnologie, Technopole de Borj Cédria (CBBC), BP 901, Hammam-Lif 2050, Tunisia,2 Penn State Berks College, P.O. Box 7009, Reading, Pennsylvania 196103

Received 10 May 2007/ Accepted 26 September 2007

Multilocus sequence typing (MLST) is a sequence-based method used to characterize bacterial genomes. This method was used to examine the genetic structure of Medicago-nodulating rhizobia at the Amra site, which is located in an arid region of Tunisia. Here the annual medics Medicago laciniata and M. truncatula are part of the natural flora. The goal of this study was to identify whether distinct chromosomal groups of rhizobia nodulate M. laciniata because of its restricted requirement for specific rhizobia. The MLST analysis involved determination of sequence variation in 10 chromosomal loci of 74 isolates each of M. laciniata and M. truncatula. M. truncatula was used as a control trap host, because unlike M. laciniata, it has relatively unrestricted rhizobial requirements. Allelic diversity among the plasmid nodC alleles in the isolates was also determined. The 148 isolates were placed into 26 chromosomal sequence types (STs), only 3 of which had been identified previously. The rhizobia of M. laciniata were shown to be part of the general Medicago-nodulating population in the soil because 99.95% of the isolates had chromosomal genotypes similar to those recovered from M. truncatula. However, the isolates recovered from M. laciniata were less diverse than those recovered from M. truncatula, and they also harbored an unusual nodC allele. This could perhaps be best explained by horizontal transfer of the different nodC alleles among members of the Medicago-nodulating rhizobial population at the field site. Evidence indicating a history of lateral transfer of rhizobial symbiotic genes across distinct chromosomal backgrounds is provided.

* Corresponding author. Mailing address: Soybean Genomics and Improvement Laboratory, HH-4, Bldg. 010, BARC-West, USDA, ARS, 10300 Baltimore Blvd., Beltsville, MD 20705. Phone: (301) 504-7280. Fax: (301) 713-0308. E-mail: peter.vanberkum{at}ars.usda.gov

{triangledown} Published ahead of print on 5 October 2007.

Applied and Environmental Microbiology, December 2007, p. 7597-7604, Vol. 73, No. 23
0099-2240/07/$08.00+0     doi:10.1128/AEM.01046-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Rangin, C., Brunel, B., Cleyet-Marel, J.-C., Perrineau, M.-M., Bena, G. (2008). Effects of Medicago truncatula Genetic Diversity, Rhizobial Competition, and Strain Effectiveness on the Diversity of a Natural Sinorhizobium Species Community. Appl. Environ. Microbiol. 74: 5653-5661 [Abstract] [Full Text]  


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