Characterization of a Ubiquitous Plasmid in Erwinia amylovora. Jacqueline Laurent,. Pathologie Végétale, 16 rue Cl.-Bernard, F-75231 Paris Cedex 05, France. Marie-Anne Barny, Alain Kotoujansky, Philippe Dufriche, and Joel L. Vanneste. Pathologie Végétale, 16 rue Cl.-Bernard, F-75231 Paris Cedex 05, France.. MPMI 2:160-164. Accepted 22 February 1989. Copyright 1989 The American Phytopathological Society.

An approximately 30-kb plasmid was present in each of 66 strains of Erwinia amylovora isolated from various hosts and areas. These plasmids from different strains proved identical to pEA28, the unique plasmid from the virulent E. amylovora strain CFBP1430. The physical map of pEA28 was established by using six restriction enzymes. To determine a possible role in pathogenicity for this plasmid, CFBP1430 was cured of pEA28: The plasmid was first labeled by a Mu-derivative transposable element and was subsequently evicted in the presence of a fragment containing putative genes for plasmid incompatibility. A function necessary for thiamine independent growth was assigned to pEA28. When the cured strain was inoculated into sensitive hosts, delayed appearance and reduced severity of symptoms were observed.