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Journal of Bacteriology, March 2007, p. 2510-2520, Vol. 189, No. 6
0021-9193/07/$08.00+0     doi:10.1128/JB.01803-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Sinorhizobium meliloti SyrA Mediates the Transcriptional Regulation of Genes Involved in Lipopolysaccharide Sulfation and Exopolysaccharide Biosynthesis{triangledown}

David H. Keating*

Department of Microbiology and Immunology, Loyola University Chicago, Maywood, Illinois 60153

Received 29 November 2006/ Accepted 26 December 2006

Sinorhizobium meliloti is a gram-negative soil bacterium found either in free-living form or as a nitrogen-fixing endosymbiont of leguminous plants such as Medicago sativa (alfalfa). S. meliloti synthesizes an unusual sulfate-modified form of lipopolysaccharide (LPS). A recent study reported the identification of a gene, lpsS, which encodes an LPS sulfotransferase activity in S. meliloti. Mutants bearing a disrupted version of lpsS exhibit an altered symbiosis, in that they elicit more nodules than wild type. However, under free-living conditions, the lpsS mutant displayed no change in LPS sulfation. These data suggest that the expression of lpsS is differentially regulated, such that it is transcriptionally repressed during free-living conditions but upregulated during symbiosis. Here, I show that the expression of lpsS is upregulated in strains that constitutively express the symbiotic regulator SyrA. SyrA is a small protein that lacks an apparent DNA binding domain and is predicted to be located in the cytoplasmic membrane yet is sufficient to upregulate lpsS transcription. Furthermore, SyrA can mediate the transcriptional upregulation of exo genes involved in the biosynthesis of the symbiotic exopolysaccharide succinoglycan. The SyrA-mediated transcriptional upregulation of lpsS and exo transcription is blocked in mutants harboring a mutation in chvI, which encodes the response regulator of a conserved two-component system. Thus, SyrA likely acts indirectly to promote transcriptional upregulation of lpsS and exo genes through a mechanism that requires the ExoS/ChvI two-component system.

* Mailing address: Department of Microbiology and Immunology, Loyola University Chicago, Building 105, 2160 S. First Avenue, Maywood, IL 60153. Phone: (708) 216-9472. Fax: (708) 216-9574. E-mail: dkeati1{at}lumc.edu.

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

Journal of Bacteriology, March 2007, p. 2510-2520, Vol. 189, No. 6
0021-9193/07/$08.00+0     doi:10.1128/JB.01803-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Mitrophanov, A. Y., Groisman, E. A. (2008). Signal integration in bacterial two-component regulatory systems. Genes Dev. 22: 2601-2611 [Abstract] [Full Text]  


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