Complementation analyses of Pseudomonas solanacearum extracellular polysaccharide mutants and identification of genes responsive to EpsR.

Many plant-pathogenic bacteria require extracellular polysaccharides (EPS) for successful infection. For example, mutations tht 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 transposon-tagged mutants and categorized 66EPS::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 lipopolysaccharide 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 EPS.