Extracellular polysaccharide is required for wild-type virulence of Pseudomonas solanacearum.

Several Pseudomonas solanacearum strains which produced no detectable extracellular polysaccharide (EPS) in planta had been reported to remain highly virulent when tested at high inoculum concentrations (P. Xu, M. Iwata, S. Leong, and L. Sequeira, J. Bacteriol. 172:3946-3951, 1990; P. Xu, S. Leong, and L. Sequeira, J. Bacteriol. 170:617-622, 1988). Two of these mutants, KD700 and KD710, have now been molecularly and genetically mapped to the EPSI gene cluster described by Denny and Baek (Mol. Plant-Microbe Interact. 4:198-206, 1991). When a range of inoculum concentrations was used, these two mutants and all other EPS-defective mutants tested were found to be reduced in virulence to eggplants and tobacco relative to the wild-type strain. Thus, EPS consistently is required for the wild-type level of virulence in P. solanacearum.