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Journal of Bacteriology, December 2005, p. 8427-8436, Vol. 187, No. 24
0021-9193/05/$08.00+0     doi:10.1128/JB.187.24.8427-8436.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

L-Canavanine Made by Medicago sativa Interferes with Quorum Sensing in Sinorhizobium meliloti

Neela D. Keshavan,1 Puneet K. Chowdhary,2 Donovan C. Haines,2 and Juan E. González1*

Department of Molecular and Cell Biology, University of Texas at Dallas, Richardson, Texas 75083-0688,1 Department of Chemistry, University of Texas at Dallas, Richardson, Texas 75083-06882

Received 11 July 2005/ Accepted 26 September 2005

Sinorhizobium meliloti is a gram-negative soil bacterium, capable of establishing a nitrogen-fixing symbiosis with its legume host, alfalfa (Medicago sativa). Quorum sensing plays a crucial role in this symbiosis, where it influences the nodulation process and the synthesis of the symbiotically important exopolysaccharide II (EPS II). S. meliloti has three quorum-sensing systems (Sin, Tra, and Mel) that use N-acyl homoserine lactones as their quorum-sensing signal molecule. Increasing evidence indicates that certain eukaryotic hosts involved in symbiotic or pathogenic relationships with gram-negative bacteria produce quorum-sensing-interfering (QSI) compounds that can cross-communicate with the bacterial quorum-sensing system. Our studies of alfalfa seed exudates suggested the presence of multiple signal molecules capable of interfering with quorum-sensing-regulated gene expression in different bacterial strains. In this work, we choose one of these QSI molecules (SWI) for further characterization. SWI inhibited violacein production, a phenotype that is regulated by quorum sensing in Chromobacterium violaceum. In addition, this signal molecule also inhibits the expression of the S. meliloti exp genes, responsible for the production of EPS II, a quorum-sensing-regulated phenotype. We identified this molecule as L-canavanine, an arginine analog, produced in large quantities by alfalfa and other legumes.

* Corresponding author. Mailing address: Department of Molecular and Cell Biology, University of Texas at Dallas, FO 3.1, Richardson, TX 75083-0688. Phone: (972) 883-2526. Fax: (630) 604-3093. E-mail: jgonzal{at}utdallas.edu.

Journal of Bacteriology, December 2005, p. 8427-8436, Vol. 187, No. 24
0021-9193/05/$08.00+0     doi:10.1128/JB.187.24.8427-8436.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Sanchez-Contreras, M., Bauer, W. D, Gao, M., Robinson, J. B, Allan Downie, J (2007). Quorum-sensing regulation in rhizobia and its role in symbiotic interactions with legumes. Phil Trans R Soc B 362: 1149-1163 [Abstract] [Full Text]  
  • Gonzalez, J. E., Keshavan, N. D. (2006). Messing with Bacterial Quorum Sensing. Microbiol. Mol. Biol. Rev. 70: 859-875 [Abstract] [Full Text]  


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