Complementation Analyses of Pseudomonas solanacearum Extracellular Polysaccharide Mutants and Identification of Genes Responsive to EpsR. Robin McWilliams . Department of Biology, Indiana University, Bloomington 47405, U.S.A. Matt Chapman, Katarzyna M. Kowalczuk, Diane Hersberger, Jin-hua Sun, and Chris Cheng Kao. Department of Biology, Indiana University, Bloomington 47405, U.S.A. MPMI 8:837-844. Accepted 28 July 1995. Copyright 1995 The American Phytopathological Society.

Many plant-pathogenic bacteria require extracellular polysaccharides (EPS) for successful infection. For example, mutations that prevent EPS production in the bacterial wilt pathogen, Pseudomonas solanacearum, will reduce the ability to wilt plants. While several P. solanacearum EPS genes have been identified and characterized, a systematic analysis of EPS mutants has not previously been performed. We have screened over 12,000 trans-poson-tagged mutants and categorized 66 EPS::lacZ mutants into nine complementation sets. Five of these are composed of previously characterized EPS structural and regulatory loci; four contain newly described EPS loci. One of the four novel complementation sets has been determined to be defective for both EPS and lipopolysac-charide production. We also used the EPS::lacZ mutants to examine the interaction between P. solanacearum EPS genes. Overexpression of the previously described regulator EpsR was found to down-regulate the expression of genes encoding production of the major acidic form of EPS.