The phylogenetic relationships of the type strains of 16 Erwinia species were investigated by performing a comparative analysis of the sequences of the 16s rRNA genes of these organisms. The sequence data were analyzed by the neighbor-joining method, and each branch was supported by moderate bootstrap values. The phylogenetic tree and sequence analyses confirmed that the genus Erwinia is composed of species that exhibit considerable heterogeneity and form four clades that are intermixed with members of other genera, such as Escherichia coli, Klebsiella pneumoniae, and Serratia marcescens. Cluster I includes the type strains of Envinia herbicola, Erwinia milletiae, Erwinia ananas, Erwinia uredovora, and Erwinia stewartii and corresponds to Dye's herbicola group. Cluster I1 consists of Erwinia persicinus, Erwinia rhapontici, Erwinia amylovora, and Erwinia cypripedii. Cluster I11 consists of Erwinia carotovora subspecies and Erwinia chrysanthemi and is characterized by the production of pectate lyases and cellulases. Envinia salicis, Erwinia rubrifaciens, and Erwinia nigrijluens form the cluster that is most distantly related to other Erwinia species. The data from the sequence analyses are discussed in the context of biochemical and DNA-DNA hybridization data.The genus Erwinia was proposed by Winslow et al. (51) for gram-negative, non-spore-forming, peritrichous, fermentative, rod-shaped bacteria, and it belongs to the family Enterobacteriaceae. This genus was proposed for plant-associated bacteria that are pathogens, saprophytes, and epiphytes.Although the heterogeneous taxonomic structure of the genus Erwinia has been discussed by using phenotypic data (13, 15-19, 31, 22, 35, 42, 44) and genotypic data (3, 6-10), the taxonomic position of this genus remains problematic (5, 32, 40, 41). Previously, Dye (15-18) classified the members of the genus Erwinia into four natural clusters. The carotovora group is characterized by soft-rot-causing and biochemically active species. Although some authors (10, 45) have proposed that this group should be designated the genus Pectobacterium and differentiated from other Erwinia species on the basis of distinct pathogenic and biochemical properties and this view was partially supported by DNA-DNA hybridization studies (9, lo), it has not been generally accepted. The amylovora group consists of pathogens that cause dry necrosis or wilt in their specific host plants, and the taxonomic position of this group as a true Erwinia group has rarely been questioned. Furthermore, Dye (15) considered members of this group subspecies (or varieties) of Erwinia amylovora. However, each species belonging to the amylovora group forms a distinct phenon, as shown in the numerical analyses of Verdonck et al. (44) and Mergaert et al. (35). In addition, DNA-DNA hybridization studies (3, 6, 7, 23, 37) indicated that Erwinia amylovora had low levels of relatedness to other species of the amylovora group, as well as other Erwinia species, and the DNA-DNA relatedness values for Erwinia salicis, Erw...
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