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Applied and Environmental Microbiology, March 2001, p. 1400-1403, Vol. 67, No. 3
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.3.1400-1403.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Genetic Evidence that Loss of Virulence Associated with gacS or gacA Mutations in Pseudomonas syringae B728a Does Not Result from Effects on Alginate Production

David K. Willis,1,* Jeremy J. Holmstadt,2 and Thomas G. Kinscherf2

Plant Disease Resistance Research Unit, U.S. Department of Agriculture---Agricultural Research Service,1 and Department of Plant Pathology, University of Wisconsin---Madison,2 Madison, Wisconsin 53706

Received 30 August 2000/Accepted 12 December 2000

Mutations in the global regulatory genes gacS and gacA render Pseudomonas syringae pv. syringae strain B728a completely nonpathogenic in foliar infiltration assays on bean plants. It had been previously demonstrated that gac genes regulate alginate production in Pseudomonas species, while other published work indicated that alginate is involved in the pathogenic interaction of P. syringae on bean plants. Together, these results suggested that the effects of gacS and gacA mutations on virulence in B728a might stem directly from a role in regulating alginate. In this report, we confirm a role for gac genes in both algD expression and alginate production in B728a. However, B728a mutants completely devoid of detectable alginate were as virulent as the wild-type strain in our assay. Thus, factors other than, or in addition to, a deficiency of alginate must be involved in the lack of pathogenicity observed with gacS and gacA mutants.

* Corresponding author. Mailing address: Plant Disease Resistance Research Unit, U.S. Department of Agriculture---Agricultural Research Service, University of Wisconsin, 1630 Linden Dr., Madison, WI 53706. Phone: (608) 262-5063. Fax: (608) 262-1541. E-mail: dkwillis{at}facstaff.wisc.edu.

Applied and Environmental Microbiology, March 2001, p. 1400-1403, Vol. 67, No. 3
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.3.1400-1403.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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