The almost complete 16S rDNA sequences of twenty nine plant-associated strains, representing species of the genera Erwinia, Pantoea and Enterobacter were determined and compared with those of other members of the Enterobacteriaceae. The species of the genus Erwinia may be divided into three phylogenetic groups. Cluster I represents the true erwinias and comprises E. amylovora, E. mallotivora, E. persicinus, E. psidii, E. rhapontici and E. tracheiphila. We propose to unite the species of cluster II, E. carotovora subsp. atroseptica, E. carotovora subsp. betavasculorum, E. carotovora subsp. carotovora, E. carotovora subsp. odorifera, E. carotovora subsp. wasabiae, E. cacticida, E. chrysanthemi and E. cypripedii in the genus Pectobacterium respectively as P. carotovorum subsp. atrosepticum comb. nov., P. carotovorum subsp. betavasculorum comb. nov., P. carotovorum subsp. carotovorum comb. nov., P. carotovorum subsp. odoriferum comb. nov., P. carotovorum subsp. wasabiae comb. nov., P. cacticidum comb. nov., P. chrysanthemi and P. cypripedii. The species E. alni, E. nigrifluens, E. paradisiaca, E. quercina, E. rubrifaciens and E. salicis, comprising cluster III, are being classified into a new genus Brenneria gen. nov. respectively as B. alni comb. nov., B. nigrifluens comb. nov., B. paradisiaca comb. nov., B. quercina comb. nov., B. rubrifaciens comb. nov. and B. salicis comb. nov. The species of the genus Pantoea, included in this study, form a monophyletic unit (cluster IV), closely related with Erwinia, whereas the three phytopathogenic species of the genus Enterobacter are scattered among the genera Citrobacter and Klebsiella.

The Pectobacteriumcarotovorum species corresponds to a complex, including two subspecies with validly published names, two proposed subspecies and two new species, Pectobacterium polaris and Pectobacterium aquaticum. Recent studies suggested that this complex needed revision. We examined the taxonomic status of 144 Pectobacterium strains isolated from a wide range of plant species, various geographical origins and waterways. Sequences of the leuS, dnaX and recA housekeeping genes clustered 114 of these Pectobacterium strains together within a not yet described clade. We sequenced eight strains of this clade and analysed them together with the 102 Pectobacterium genomes available in the NCBI database. Phylogenetic analysis, average nucleotide identity calculation and in silico DNA-DNA hybridization allowed us to differentiate seven clades. This led us to propose the elevation of Pectobacterium carotovorumsubsp. odoriferum to species level as Pectobacteriumodoriferum sp. nov. (type strain CFBP 1878T=LMG 5863T=NCPPB 3839T=ICMP 11533T), the proposal of Pectobacteriumactinidiae sp. nov. (type strain KKH3=LMG 26003 T=KCTC 23131T) and Pectobacteriumbrasiliense sp. nov. (type strain CFBP 6617T= LMG 21371T=NCPPB 4609T), to emend the description of Pectobacterium carotovorum (type strain CFBP 2046T=LMG 2404T=NCPPB 312T=ICMP 5702T), and to propose a novel species, Pectobacterium versatile sp. nov (type strain CFBP6051T= NCPPB 3387T=ICMP 9168T) which includes the strains previously described as 'Candidatus Pectobacterium maceratum'. Phenotypic analysis performed using Biolog GENIII plates on eight strains of P. versatile sp. nov. and related strains completed our analysis.

A collection of 42 strains belonging to the five subspecies of Pectobacterium carotovorum (subspecies atrosepticum, betavasculorum, carotovorum, odoriferum and wasabiae) and 11 reference and type strains of biovars of Pectobacterium chrysanthemi, Pectobacterium cacticidum and Brenneria paradisiaca were studied by DNA-DNA hybridization, numerical taxonomy of 120 phenotypic characteristics, serology and new phylogenetic analysis of previously reported sequences from a database of aligned 16S rDNA sequences. The P. carotovorum subspecies formed a clade according to neighbour-joining methods, but they formed two paraphyletic clusters according to maximum-likelihood and maximum-parsimony. However, phylogenetic analysis of 16S rDNA sequences alone is not sufficient to justify generic differentiation and therefore, it is proposed to retain the P. carotovorum subspecies in the genus Pectobacterium. The strains of P. carotovorum were distributed in four genomospecies: genomospecies 1, harbouring all strains of subsp. atrosepticum, genomospecies 2, including the strains of subsp. betavasculorum isolated from sugar beet, sunflower, potato, hyacinth and artichoke, genomospecies 3, clustering all strains of subsp. wasabiae isolated from wasabi in Japan, and genomospecies 4, gathering together strains of subsp. carotovorum and strains of subsp. odoriferum. Four strains of P. carotovorum subsp. carotovorum remained unclustered. Biochemical criteria, deduced from a numerical taxonomy study of phenotypic characteristics and serological reactions, allowed discrimination of strains belonging to the four genomospecies. Thus, it is proposed that three genomospecies be elevated to species level as Pectobacterium atrosepticum sp. nov. (type strain CFBP 1526T =LMG 2386T =NCPPB 549T =ICMP 1526T), Pectobacterium betavasculorum sp. nov. (type strain CFBP 2122T =LMG 2464T =NCPPB 2795T =ICMP 4226T) and Pectobacterium wasabiae sp. nov. (type strain CFBP 3304T =LMG 8404T =NCPPB 3701T =ICMP 9121T). Only two subspecies are maintained within P. carotovorum, subsp. carotovorum (type strain CFBP 2046T =LMG 2404T =NCPPB 312T =ICMP 5702T) and subsp. odoriferum (type strain CFBP 1878T =LMG 5863T =NCPPB 3839T = ICMP 11553T), for which discriminating tests are available.