Elevation of three subspecies of Pectobacterium carotovorum to species level:: Pectobacterium atrosepticum sp nov., Pectobacterium betavasculorum sp nov and Pectobacterium wasabiae sp nov.

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 1526(T) = LMG 2386(T) = NCPPB 549(T) =ICMP 1526(T)), Pectobacterium betavasculorum sp. nov. (type strain CFBP 2122(T) = LMG 2464(T) = NCPPB 2795(T) =ICMP 4226(T)) and Pectobacterium wasabiae sp. nov. (type strain CFBP 3304(T) = LMG 8404(T) = NCPPB 3701(T) =ICMP 9121(T)). Only two subspecies are maintained within P. carotovorum, subsp. carotovorum (type strain CFBP 2046(T) = LMG 2404(T) = NCPPB 312(T) = ICMP 5702(T)) and subsp. odoriferum (type strain CFBP 1878(T) = LMG 5863(T) =NCPPB 3839(T) = ICMP 11553(T)), for which discriminating tests are available.