A comprehensive DNA-DNA hybridization study was performed by using 183 strains of the genus Xanthomonus. This genus was shown to comprise 20 DNA homology groups which are considered genomic species. Four groups corresponded to the previously described species Xanthomonas albilineans, Xanthomonas fiagariae, Xanthomonas oryzae, and Xanthomonas populi. The previously described species Xanthomonas campestris was heterogeneous and was divided into 16 DNA homology groups. One of these groups exhibited a high level of DNA homology with Xanthomonas axonopodis. The 62 pathovars represented in this study were. allocated to appropriate species. Our results, together with previous taxonomic data, supported a comprehensive revision of the classification of the genus Xanthomonas. The species X. albilineans, X. jiagarke, X. oryme, and X. populi are not affected. The type species of the genus,X. campestris (Pammell895) Dowson 1939, is emended to include only the pathovars obtained from crucifers (i.e., X. campestris pv. aberrans, X. campestris pv. armoraciae, X. campestris pv. barbareae, X. campestris pv. campestris, X. campestris pv. incanae, and X. campestris pv. raphani). vesicatoria. Differentiating characteristics were determined for the new species on the basis of metabolic activity on a range of carbon substrates by using the Biolog GN microplate system. X. axonopodisIn the past, the taxonomy of bacteria has been dominated by a phenetic approach, and many classification systems have been and still are based on what were thought to be important phenotypic properties. The taxonomy of the genus Xanthomonas has followed this tendency in that a single phenotypic feature, host specificity, has determined the classification of the genus. Since the first report of a xanthomonad (55) until 1974, it was common practice to define a plant-pathogenic xanthomonad isolated from a new host plant as a new Xanthomonas species. The unreasonable number of nomenspecies resulting from this practice was drastically reduced by Dye and Lelliott (19), who justified their reclassification by referring to the impossibility of differentiating nomenspecies by any feature other than host specificity (10,17). Later, names of former nomenspecies were preserved in a special-purpose classification (18) as Xanthomonas campestris pathovar names.The original classification of the genus Xanthomonas, in which all of the phytopathological variants of X campestris were recognized as separate species, was not sound taxonomically. With the exception of the ambiguous feature of host specificity, few biochemical and phenotypic characteristics were used to differentiate the species. In the last few years, * Corresponding author. Mailing address: Laboratorium voor Microbiologie, Universiteit Gent, Ledeganckstraat 35, B-9000 Ghent, Belgium.workers have provided evidence that the current classification, in whichX. campestris contains more than 140 pathovars, is not a reflection of genomic relationships. The first DNA hybridization experiments performed with Xanthomonas...

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We analyzed the usefulness of rpoA, recA, and pyrH gene sequences for the identification of vibrios. We sequenced fragments of these loci from a collection of 208 representative strains, including 192 well-documented Vibrionaceae strains and 16 presumptive Vibrio isolates associated with coral bleaching. In order to determine the intraspecies variation among the three loci, we included several representative strains per species. The phylogenetic trees constructed with the different genetic loci were roughly in agreement with former polyphasic taxonomic studies, including the 16S rRNA-based phylogeny of vibrios. The families Vibrionaceae, Photobacteriaceae, Enterovibrionaceae, and Salinivibrionaceae were all differentiated on the basis of each genetic locus. Each species clearly formed separated clusters with at least 98, 94, and 94% rpoA, recA, and pyrH gene sequence similarity, respectively. The genus Vibrio was heterogeneous and polyphyletic, with Vibrio fischeri, V. logei, and V. wodanis grouping closer to the Photobacterium genus. V. halioticoli-, V. harveyi-, V. splendidus-, and V. tubiashii-related species formed groups within the genus Vibrio. Overall, the three genetic loci were more discriminatory among species than were 16S rRNA sequences. In some cases, e.g., within the V. splendidus and V. tubiashii group, rpoA gene sequences were slightly less discriminatory than recA and pyrH sequences. In these cases, the combination of several loci will yield the most robust identification. We can conclude that strains of the same species will have at least 98, 94, and 94% rpoA, recA, and pyrH gene sequence similarity, respectively.Vibrios are gram-negative, usually motile rods, are mesophilic and chemoorganotrophic, and have a facultatively fermentative metabolism (5). They are generally able to grow on marine agar and on the selective medium thiosulfate-citratebile salt-sucrose agar and are mostly oxidase positive. Vibrios belong to the Gammaproteobacteria according to 16S rRNA gene sequence analysis. These bacteria are found abundantly in aquatic habitats and in association with eukaryotes. Associations established by vibrios range from mutualistic, e.g., Vibrio fischeri-bobtail squid (26), to pathogenic, e.g., V. cholerae-humans (45). Probiotic Vibrio strains for fish and shellfish have also been documented (44).The current family Vibrionaceae comprises the genera Enterovibrio (2 species), Grimontia (1 species), Photobacterium (7 species), Salinivibrio (1 species), and Vibrio (64 species). The novel species Photobacterium rosenbergii and Enterovibrio coralii have recently been proposed to encompass isolates associated with coral bleaching (41). Several new Vibrio species, mainly in the phylogenetic neighborhood of V. harveyi, V. halioticoli, V. splendidus, V. tubiashii, and V. fluvialis, have been described in the last few years, with V. neonatus, V. ezurae (28), and V. ponticus (22) being the most recent ones. V. harveyi, V. splendidus, and V. tubiashii are frequently associated with disease in different spe...

Hybridization experiments were carried out between DNAs from more than 70 strains of Campylobacter spp. and related taxa and either 3H-labeled 23s rRNAs from reference strains belonging to Campylobacter fetus, Campylobacter concisus, Campylobacter sputorum, Campylobacter coli, and Campylobacter nitrofigilis, an unnamed Campylobacter sp. strain, and a Wolinella succinogenes strain or 3H-or 14C-labeled 23s rRNAs from 13 gram-negative reference strains. An immunotyping analysis of 130 antigens versus 34 antisera of campylobacters and related taxa was also performed. We found that all of the named campylobacters and related taxa belong to the same phylogenetic group, which we name rRNA superfamily VI and which is far removed from the gram-negative bacteria allocated to the five rRNA superfamilies sensu De Ley. There is a high degree of heterogeneity within this rRNA superfamily. Organisms belonging to rRNA superfamily VI should be reclassified in several genera. We propose that the emended genus Campylobacter should be limited to Campylo bacter fetus, Campylo bacter hy oin testinalis , Campylo bacter concisus, Campylo bacter m ucosalis , Campylobacter sputorum, Campylobacter jejuni, Campylobacter coli, Campylobacter lari, and "Campylobacter upsaliensis. " Wolinella curva and Wolinella recta are transferred to the genus Campylobacter as Campylobacter curvus comb. nov. and Campylobacter rectus comb. nov., respectively. Bacteroides gracilis and Bacteroides ureolyticus are generically misnamed and are closely related to the genus Campylobacter. Campylobacter nitrofigilis, Campylobacter cryaerophila, and an unnamed Campylobacter sp. strain constitute a new genus, for which the name Arcobacter is proposed; this genus contains two species, Arcobacter nitrofigilis comb. nov. (type species) and Arcobacter cryaerophilus comb. nov. Wolinellu succinogenes so far is the only species of the genus Wolinella. The genus Helicobacter is also emended; Campylobacter cinaedi and Campylobacter fennelliae are included in this genus as Helicobacter cinaedi comb. nov. and Helicobacter fennelliae comb. nov., respectively. The genus "Flexispira," with "Flexispira rappini" as the only species, is closely related to the genus Helicobacter. The free-living, sulfur-reducing campylobacters do not belong to any of these genera; they probably constitute a distinct genus within rRNA superfamily VI.At present, the genus Campylobacter consists of 13 welldefined species (40). Recently, two additional species, Campylobacter pylori and Campylobacter mustelae, were included in the new genus Helicobacter as Helicobacter pylori and Helicobacter mustelae, respectively (20). The clinical significance of all of these organisms was reviewed recently by Penner (40). A study of the taxonomic structure of the genus Campylobacter in which partial 16s rRNA sequence analysis was used revealed that the Campylobacter species can be divided into three major rRNA homology groups (58 It was the aim of this study to include all known campylobacters and possible relatives in...

Vibrio sp. YB1T (=ATCC BAA-450 T =LMG 20984 T ), the aetiological agent of tissue lysis of the coral Pocillopora damicornis, was characterized as a novel Vibrio species on the basis of 16S rDNA sequence, DNA-DNA hybridization data (G+C content is 45?6 mol%), AFLP and GTG 5 -PCR genomic fingerprinting patterns and phenotypic properties, including the cellular fatty acid profile. The predominant fatty acids were 16 : 0 and 18 : 1w7c. The name Vibrio coralliilyticus sp. nov. is proposed for the novel coral-pathogenic species. In addition to strain YB1 T , which was isolated from the Indian Ocean, five additional strains of V. coralliilyticus have been isolated, three from diseased P. damicornis in the Red Sea, one from diseased oyster larvae (Kent, UK) and one from bivalve larvae (Brazil). The six V. coralliilyticus strains showed high genotypic and phenotypic similarities and all were pathogenic to P. damicornis. The closest phylogenetic neighbours to V. coralliilyticus are Vibrio tubiashii, Vibrio nereis and Vibrio shilonii.