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Genetic Analysis of a Pathogenic Erwinia sp. Isolated from Pear in Japan

Four Erwinia strains, originally isolated in Japan from pear trees with bacterial shoot blight symptoms, were analyzed to determine their genetic relationship with Erwinia amylovora and E. pyrifoliae. When genomes were characterized with amplified fragment length polymorphism markers and by comparative groEL sequence analysis, the Japanese Erwinia sp. and South Korean E. pyrifoliae strains were placed in the same group, which was phylogenetically distinct from a group of 15 strains of E. amylovora. Sequencing of the 29,593-bp plasmid pEJ30 from Erwinia strain Ejp556 revealed that this plasmid was nearly identical to plasmid pEP36 from E. pyrifoliae and was closely related to the nontransferable ubiquitous plasmid pEA29 from E. amylovora. Twenty-one presumptive genes and their order in pEP36 were highly conserved in pEJ30; however, transposon Tn5394, which was present in pEP36, was not found in pEJ30. Short-sequence DNA repeats were conserved between pEJ30 and pEP36, and were different from short-sequence repeats in pEA29. Despite base-pair mismatches, primer pairs used in pEA29 polymerase chain reaction assays for E. amylovora amplified plasmid DNA from the Japanese Erwinia Ejp556 and Ejp562. Like E. pyrifoliae and a few strains of E. amylovora, Japanese Erwinia Ejp617 contained plasmids related to E. pyrifoliae ColE1-related plasmid pEP2.6. Based on these genetic analyses, we conclude that the Erwinia pathogen of pear in Japan is closely related to E. pyrifoliae and that both of these pathogens are demonstrably distinct from E. amylovora.