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Applied and Environmental Microbiology, June 2007, p. 3779-3786, Vol. 73, No. 12
0099-2240/07/$08.00+0     doi:10.1128/AEM.02999-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Using the Ralstonia solanacearum Tat Secretome To Identify Bacterial Wilt Virulence Factors{triangledown} ,{dagger}

Enid T. González,{ddagger} Darby G. Brown,§ Jill K. Swanson, and Caitilyn Allen*

Department of Plant Pathology, University of Wisconsin, Madison, Wisconsin

Received 28 December 2006/ Accepted 11 April 2007

To identify secreted virulence factors involved in bacterial wilt disease caused by the phytopathogen Ralstonia solanacearum, we mutated tatC, a key component of the twin-arginine translocation (Tat) secretion system. The R. solanacearum tatC mutation was pleiotropic; its phenotypes included defects in cell division, nitrate utilization, polygalacturonase activity, membrane stability, and growth in plant tissue. Bioinformatic analysis of the R. solanacearum strain GMI1000 genome predicted that this pathogen secretes 70 proteins via the Tat system. The R. solanacearum tatC strain was severely attenuated in its ability to cause disease, killing just over 50% of tomato plants in a naturalistic soil soak assay where the wild-type parent killed 100% of the plants. This result suggested that elements of the Tat secretome may be novel bacterial wilt virulence factors. To identify contributors to R. solanacearum virulence, we cloned and mutated three genes whose products are predicted to be secreted by the Tat system: RSp1521, encoding a predicted AcvB-like protein, and two genes, RSc1651 and RSp1575, that were identified as upregulated in planta by an in vivo expression technology screen. The RSc1651 mutant had wild-type virulence on tomato plants. However, mutants lacking either RSp1521, which appears to be involved in acid tolerance, or RSp1575, which encodes a possible amino acid binding protein, were significantly reduced in virulence on tomato plants. Additional bacterial wilt virulence factors may be found in the Tat secretome.

* Corresponding author. Mailing address: Department of Plant Pathology, University of Wisconsin, 1630 Linden Drive, Madison, WI 53706. Phone: (608) 262-9578. Fax: (608) 263-2626. E-mail: cza{at}plantpath.wisc.edu

{triangledown} Published ahead of print on 27 April 2007.

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

{ddagger} Present address: United States Department of Agriculture-Agricultural Research Service, Crops Pathology and Genetics Research Unit, Department of Plant Pathology, University of California, Davis, CA 95616.

§ Present address: University of Auckland, School of Biological Sciences, Private Bag 92019, Auckland 1020, New Zealand.

Applied and Environmental Microbiology, June 2007, p. 3779-3786, Vol. 73, No. 12
0099-2240/07/$08.00+0     doi:10.1128/AEM.02999-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.





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