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Journal of Bacteriology, October 2009, p. 5890-5900, Vol. 191, No. 19
0021-9193/09/$08.00+0     doi:10.1128/JB.00760-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

The Novel Genes emmABC Are Associated with Exopolysaccharide Production, Motility, Stress Adaptation, and Symbiosis in Sinorhizobium meliloti{triangledown} ,{dagger}

Jennifer Morris and Juan E. González*

Department of Molecular and Cell Biology, University of Texas at Dallas, Richardson, Texas 75080-0688

Received 11 June 2009/ Accepted 17 July 2009

The nitrogen-fixing symbiont Sinorhizobium meliloti senses and responds to constantly changing environmental conditions as it makes its way through the soil in search of its leguminous plant host, Medicago sativa (alfalfa). As a result, this bacterium regulates various aspects of its physiology in order to respond appropriately to stress, starvation, and competition. For example, exopolysaccharide production, which has been shown to play an important role in the ability of S. meliloti to successfully invade its host, also helps the bacterium withstand osmotic changes and other environmental stresses. In an effort to further elucidate the intricate regulation of this important cell component, we set out to identify genetic factors that may affect its production. Here we characterize novel genes that encode a small protein (EmmA) and a putative two-component system (EmmB-EmmC). A mutation in any of these genes leads to increased production of the symbiotically important exopolysaccharide succinoglycan. In addition, emm mutants display membrane-associated defects, are nonmotile, and are unable to form an optimal symbiosis with alfalfa, suggesting that these novel genes may play a greater role in the overall fitness of S. meliloti both during the free-living stage and in its association with its host.

* Corresponding author. Mailing address: RL11, 800 W. Campbell Road, University of Texas at Dallas, Richardson, TX 75080-0688. Phone: (972) 883-2526. Fax: (972) 883-2409. E-mail: jgonzal{at}utdallas.edu

{triangledown} Published ahead of print on 24 July 2009.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, October 2009, p. 5890-5900, Vol. 191, No. 19
0021-9193/09/$08.00+0     doi:10.1128/JB.00760-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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