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Journal of Bacteriology, April 2009, p. 2133-2143, Vol. 191, No. 7
0021-9193/09/$08.00+0     doi:10.1128/JB.01567-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Role of Potassium Uptake Systems in Sinorhizobium meliloti Osmoadaptation and Symbiotic Performance{triangledown}

Ana Domínguez-Ferreras, Socorro Muñoz, José Olivares, María J. Soto, and Juan Sanjuán*

Departamento de Microbiología del Suelo y Sistemas Simbióticos, Estación Experimental del Zaidín, CSIC, Granada, Spain

Received 4 November 2008/ Accepted 23 January 2009

Stimulation of potassium uptake is the most rapid response to an osmotic upshock in bacteria. This cation accumulates by a number of different transport systems whose importance has not been previously addressed for rhizobia. In silico analyses reveal the presence of genes encoding four possible potassium uptake systems in the genome of Sinorhizobium meliloti 1021: Kup1, Kup2, Trk, and Kdp. The study of the relevance of these systems under a number of different growth conditions and in symbiosis showed that the integrity of Kup1 or Trk is essential for growth under laboratory conditions even in osmotically balanced media and the absence of both systems leads to a reduced infectivity and competitiveness of the bacteria in alfalfa roots. Trk is the main system involved in the accumulation of potassium after an osmotic upshift and the most important system for growth of S. meliloti under hyperosmotic conditions. The other three systems, especially Kup1, are also relevant during the osmotic adaptation of the cell, and the relative importance of the Kdp system increases at low potassium concentrations.

* Corresponding author. Mailing address: Estación Experimental del Zaidín, CSIC, Prof. Albareda 1, E-18008 Granada, Spain. Phone: 34-958-181600, ext. 259. Fax: 34-958-129600. E-mail: juan.sanjuan{at}eez.csic.es

{triangledown} Published ahead of print on 30 January 2009.

Journal of Bacteriology, April 2009, p. 2133-2143, Vol. 191, No. 7
0021-9193/09/$08.00+0     doi:10.1128/JB.01567-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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