The different nutritional properties of several Desulfovibrio desulfuricans strains suggest that either the strains are misclassified or there is a high degree of phenotypic diversity within the genus Desulfovibrio. The obligately anaerobic, dissimilatory, sulfate-reducing bacteria utilize sulfate as their terminal electron acceptor and derive their energy for growth from the oxidation of organic compounds and hydrogen gas (27). Among the genera of sulfate-reducing bacteria, perhaps the most thoroughly studied species are classified in the genus Desulfovibrio. The Desulfovibrio species which have been characterized are nutritionally similar; they are readily enriched with lactate or hydrogen and utilize only a few other substrates (38). Diagnostically, Desulfovibrio species test positive (with some exceptions) for the sulfite reductase desulfoviridin and contain the unique tetraheme cytochrome C3 (27). These observations have contributed to the notion that although the sulfate-reducing bacteria are ecologically very significant, they comprise a small and nutritionally limited group. However, recent isolations and descriptions of new genera have dispelled this view (38). At present, more than 10 genera of sulfate-reducing eubacteria (one of which is affiliated with gram-positive bacteria) and an extremely thermophilic sulfate-reducing archaebacterium have been described (36, 39).While the nutritional versatility and phylogenetic diversity of the sulfate-reducing bacteria have been established, questions of relatedness among species of the genus Desulfovibrio remain unanswered. Postgate has stated that the "taxonomic picture" of the genus is "imperfect" (27

A novel Gram-stain-negative strain, designated ZYY5T, was isolated from rice roots. Results of 16S rRNA gene analysis indicated that strain ZYY5T was a member of the genus Dickeya , with a highest similarity to Dickeya zeae DSM 18068T (98.5%). The major fatty acids were summed feature 3 (C16:1 ω7c and/or C16:1 ω6c), C16:0 and summed feature 8 (C18:1 ω7c and/or C18:1 ω6c). Multi-locus sequence analysis using five concatenated genes (16S rRNA, atpD, infB, recA and gyrB) and phylogenomic analysis based on 2940 core gene sequences showed that strain ZYY5T formed a robust cluster with strains EC1, ZJU1202, DZ2Q, NCPPB 3531 and CSL RW192, while separated from the other strains of D. zeae . The orthologous average nucleotide identity (ANI) and digital DNA–DNAhybridization (dDDH) values among these six strains ranged from 96.8–99.9% and 73.7–99.8%, which supported that they were belonged to the same species. However, strain ZYY5T shared 58.4 of dDDH and 94.5% of ANI values with type strain D. zeae DSM 18068T, which were lower than the proposed species boundary cut-off for dDDH and ANI. The genomic analysis revealed that strain ZYY5T contained virulence-associated genes, which is same as the phylogenetic-related strains of the genus Dickeya . Based on the results of the polyphasic approaches, we propose that strain ZYY5T represents a novel species in the genus Dickeya , for which the name Dickeya oryzae sp. nov. (=JCM 33020 T=ACCC 61554 T) is proposed. Strains EC1, ZJU1202, DZ2Q, NCPPB 3531 and CSL RW192 should also be classified in the same genomospecies of D. oryzae same as ZYY5T.