Characterization of Pseudomonas solanacearum Tn5 Mutants Deficient in Extracellular Polysaccharide. Timothy P. Denny. Department of Plant Pathology, University of Georgia, Athens 30602 U.S.A.. Felister W. Makini, and Stevens M. Brumbley. Department of Plant Pathology, University of Georgia, Athens 30602 U.S.A.. MPMI 1:215-223. Accepted 13 June 1988. Copyright 1988 The American Phytopathological Society.

Pseudomonas solanacearum produces copious amounts of extracellular polysaccharide (EPS) that may be largely responsible for the wilt symptoms typical of infections by this phytopathogenic bacterium. To test this hypothesis, we generated multiple Tn5 mutants of strains 82N and AW1 that were either impaired in production of EPS (EPSⁱ) or were EPS^- in culture, and tested them for a variety of cultural traits, for virulence on tomato, and for EPS production in planta. The Tn5 mutants were compared with the virulent parental strains and their pleiotropic, spontaneous EPS^- mutants that do not wilt tomato. Southern blot analysis confirmed that each mutant contained only one Tn5 insertion, and transformation with genomic DNA from each Tn5 mutant demonstrated that each Tn5 insertion was linked to the EPS deficiency. The mutants of strain 82N varied in the amount of EPS they produced in culture and in their ability to wilt tomato plants. The mutants, however, appeared to be pleiotropic, which precluded making conclusions regarding the involvement of EPS in symptom expression. Four EPSⁱ mutants of strain AW1 could not be differentiated in culture from the parental strain except by their lack of EPS. Three of these mutants retained their ability to wilt tomato plants, but also produced almost wild-type levels of EPS in planta. The fourth EPSⁱ mutant of AW1 produced little EPS in tomato and was reduced in its ability to cause wilt symptoms. One Tn5 mutant of AW1, which was EPS^- in culture and in planta, mimicked the pleiotropic, spontaneous EPS^- mutant in every way, including the inability to wilt tomato plants. The results from the EPSⁱ mutants of strain AW1 support the hypothesis that EPS production by this pathogen has a significant role in pathogenesis.