INVOLVEMENT OF BACTERIAL POLYSACCHARIDES IN PLANT PATHOGENESIS

Virulence of phytopathogenic bacteria is often correlated with their ability to produce extracellular polysaccharides (EPSs). The composition and amount of lipopolysaccharide O-antigens and low molecular weight, cell-associated beta-linked glucans may also affect virulence of Gram-negative pathogens. For a few species of Agrobacterium, Clavibacter, Erwinia, Pseudomonas, and Xanthomonas sufficient biochemical and genetical data has accumulated to permit critical evaluation of possible functions of polysaccharides during pathogenesis. It is dear that EPSs are necessary for several pathogens to cause normal disease symptoms such as water-soaking and wilting. Evidence is accumulating that EPSs and cell-associated polysaccharides also promote colonization and enhance survival of some bacteria within host tissues. Further progress will require the use of thoroughly characterized polysaccharide-minus mutants, ''natural'' inoculation procedures, and careful monitoring of the fate of bacteria within plants.