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Applied and Environmental Microbiology, January 2009, p. 446-453, Vol. 75, No. 2
0099-2240/09/$08.00+0     doi:10.1128/AEM.02207-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Regulatory and DNA Repair Genes Contribute to the Desiccation Resistance of Sinorhizobium meliloti Rm1021 {triangledown}

Jodi L. Humann, Hope T. Ziemkiewicz, Svetlana N. Yurgel, and Michael L. Kahn*

Institute of Biological Chemistry, Washington State University, Pullman, Washington 99164-6340

Received 24 September 2008/ Accepted 14 November 2008

Sinorhizobium meliloti can form a nitrogen-fixing symbiotic relationship with alfalfa after bacteria in the soil infect emerging root hairs of the growing plant. To be successful at this, the bacteria must be able to survive in the soil between periods of active plant growth, including when conditions are dry. The ability of S. meliloti to withstand desiccation has been known for years, but genes that contribute to this phenotype have not been identified. Transposon mutagenesis was used in combination with novel screening techniques to identify four desiccation-sensitive mutants of S. meliloti Rm1021. DNA sequencing of the transposon insertion sites identified three genes with regulatory functions (relA, rpoE2, and hpr) and a DNA repair gene (uvrC). Various phenotypes of the mutants were determined, including their behavior on several indicator media and in symbiosis. All of the mutants formed an effective symbiosis with alfalfa. To test the hypothesis that UvrC-related excision repair was important in desiccation resistance, uvrA, uvrB, and uvrC deletion mutants were also constructed. These strains were sensitive to DNA damage induced by UV light and 4-NQO and were also desiccation sensitive. These data indicate that uvr gene-mediated DNA repair and the regulation of stress-induced pathways are important for desiccation resistance.

* Corresponding author. Mailing address: P.O. Box 646340, Pullman, WA 99164-6340. Phone: (509) 335-8327. Fax: (509) 335-7643. E-mail: kahn{at}wsu.edu

{triangledown} Published ahead of print on 21 November 2008.

Applied and Environmental Microbiology, January 2009, p. 446-453, Vol. 75, No. 2
0099-2240/09/$08.00+0     doi:10.1128/AEM.02207-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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