Cloning of a Bacteriophage Polysaccharide Depolymerase Gene and Its Expression in Erwinia amylovora. John S. Hartung. Department of Botany and Plant Pathology, Michigan State University, East Lansing, Michigan 48824-1312, U.S.A.. Dennis W. Fulbright, and Edward J. Klos. Department of Botany and Plant Pathology, Michigan State University, East Lansing, Michigan 48824-1312, U.S.A.. MPMI 1:87-93. Accepted 7 January 1988. Copyright 1988 The American Phytopathological Society.

A bacteriophage gene encoding a depolymerase specific for the surface polysaccharides of Erwinia amylovora was cloned and expressed in Escherichia coli. When overlaid with a lawn of E. amylovora, an E. coli colony harboring this plasmid was surrounded by a large halo as well as a shallow depression, characteristics of the margins of plaques produced by infection of E. amylovora with this bacteriophage. Hybridization experiments confirmed the phage origin of the cloned DNA. Introduction of the cloned DNA into E. amylovora by transformation altered colony morphology. Chemical analysis showed that the cells transformed with the plasmid encoding the depolymerase produced less ethanol precipitable slime and capsular polysaccharides and that the polysaccharides were of lower molecular weight than the polysaccharides from untransformed cells or cells transformed with the vector plasmid. E. amylovora cells carrying the plasmid produced necrotic lesions in pear fruit during pathogenicity studies. However, ooze production, a classic symptom of the disease, was eliminated. This indicated that tissue death, but not the characteristic symptom of ooze production, occurred in the presence of polysaccharide depolymerase.