Vibrio pectenicida sp. nov., a pathogen of scallop (Pecten maximus) larvae.

Five strains were isolated from moribund scallop (Pecten maximus) larvae over 5 years (1990-1995) during outbreaks of disease in a hatchery (Argenton, Brittany, France). Their pathogenic activity on scallop larvae was previously demonstrated by experimental exposure. The phenotypic and genotypic features of the strains were identical. The G + C content of the strains was in the range 39-41 mol%. DNA-DNA hybridization showed a minimum of 73% intragroup relatedness. Phylogenetic analysis of small-subunit rRNA sequences confirmed that these strains should be affiliated within the family Vibrionaceae and that they are closely related to Vibrio tapetis and Vibrio splendidus. Phenotypic and genotypic analyses revealed that the isolates were distinct from these two vibrios and so constitute a new species in the genus Vibrio. They utilized only a limited number of organic substrates as sole carbon sources, including betaine and rhamnose, but did not utilize glucose and fructose. In addition, their responses were negative for indole, acetoin, decarboxylase and dihydrolase production. The name Vibrio pectenicida is proposed for the new species; strain A365 is the type strain (= CIP 105190T).

Roseobacter gallaeciensis sp. nov., a new marine bacterium isolated from rearings and collectors of the scallop Pecten maximus.

Four bacterial strains were isolated from larval cultures and collectors of the scallop Pecten maximus. They showed a high level of intragroup genomic relatedness (84-95%) as determined by DNA-DNA hybridization. The cells were Gram-negative, strictly aerobic, motile, ovoid rods. They grew at temperatures from 15 to 37 degrees C and from pH 7.0 to 10, but did not grow in the absence of NaCl and required growth factors. They had the ability to use a wide variety of compounds as sole carbon source: D-mannose, D-galactose, D-fructose, D-glucose, D-xylose, melibiose, trehalose, maltose, cellobiose, sucrose, mesoerythritol, D-mannitol, glycerol, D-sorbitol, meso-inositol, succinate, propionate, butyrate, gamma-aminobutyrate, DL-hydroxybutyrate, 2-ketoglutarate, pyruvate, fumarate, glycine, L-alpha-alanine, beta-alanine, L-glutamate, L-arginine, L-lysine, L-ornithine and L-proline. They exhibited oxidase and catalase activities but no denitrification activity. The isolates did not contain bacteriochlorophyll a. The G + C content ranged from 57.6 to 58 mol%. Phylogenetic analyses of the 16S rRNA sequence revealed that these isolates belong to the genus Roseobacter. On the basis of quantitative hybridization data, it is proposed that these isolates should be placed in a new species, Roseobacter gallaeciensis. The type strain is Roseobacter gallaeciensis BS107T (= CIP 105210T).

Desulfurobacterium thermolithotrophum gen. nov., sp. nov., a novel autotrophic, sulphur-reducing bacterium isolated from a deep-sea hydrothermal vent.

A thermophilic, anaerobic, strictly autotrophic, sulphur-reducing bacterium, designated BSAT (T = type strain), was isolated from a deep-sea hydrothermal chimney sample collected at the mid-Atlantic ridge. Gram-negative cells occurred singly or in pairs as small highly motile rods. Spores were not observed. The temperature range for growth was 40 to 75 degrees C, with an optimum at 70 degrees C. The pH range for growth at 70 degrees C was from 4.4 to 7.5, with an optimum around 6.0. The sea salt concentration range for growth was 15-70 gI(-1) with an optimum at 35 gI(-1). Elemental sulphur, thiosulphate and sulphite were reduced to hydrogen sulphide. Sulphate and cystine were not reduced. The G+C content of the genomic DNA was 35 mol%. Phylogenetic analyses of the 16S rRNA gene indicated that the strain was a member of the domain Bacteria and formed a branch that was almost equidistant from members of the orders Aquificales and Thermotogales. The new organism possesses phenotypic and phylogenetic traits that do not allow its classification as a member of any previously described genus; therefore, it is proposed that this isolate should be described as a member of a novel species of a new genus, Desulfurobacterium gen. nov., of which Desulfurobacterium thermolithotrophum sp. nov. is the type species. The type strain is BSAT (= DMS 11699T).

Thermosipho melanesiensis sp. nov., a new thermophilic anaerobic bacterium belonging to the order Thermotogales, isolated from deep-sea hydrothermal vents in the southwestern Pacific Ocean.

A new thermophilic, anaerobic rod-shaped bacterium, strain BI429T was isolated from the gills of a deep-sea vent hydrothermal mussel, Bathymodiolus brevior, from the Lau Basin (Southwestern Pacific Ocean). Phenotypically, this isolate exhibited characteristics similar to those described for members of the order Thermotogales. This organism was identified as a member of the genus Thermosipho on the basis of the presence of the typical outer sheath-like structure (toga), its 16S rRNA sequence, and its ability to grow on carbohydrates (sucrose, starch, glucose, maltose, lactose, cellobiose, and galactose). The cells of this organism were gram negative and rod shaped and generally occurred singly or in pairs, rarely occurring as chains with a maximum of five rods. At the optimum temperature for growth (70 degrees C), optimum pH (6.5), and optimum salinity (30 g of NaCl per liter), the doubling time was 100 min. In spite of the high percentage of similarity of its 16S rRNA sequence with that of Thermosipho africanus (98.6%), the weak level of DNA-DNA reassociation with this strain (2%) and particular physiological characteristics allowed us to differentiate this new organism from the sole species of the genus Thermosipho previously described (T. africanus). On the basis of these observations, we propose that the new organism should be described as a new species, Thermosipho melanesiensis. The type strain of T. melanesiensis is BI429.

Sequence heterogeneities among 16S ribosomal RNA sequences, and their effect on phylogenetic analyses at the species level.

We have analyzed what phylogenetic signal can be derived by small subunit rRNA comparison for bacteria of different but closely related genera (enterobacteria) and for different species or strains within a single genus (Escherichia or Salmonella), and finally how similar are the ribosomal operons within a single organism (Escherichia coli). These sequences have been analyzed by neighbor-joining, maximum likelihood, and parsimony. The robustness of each topology was assessed by bootstrap. Sequences were obtained for the seven rrn operons of E. coli strain PK3. These data demonstrated differences located in three highly variable domains. Their nature and localization suggest that since the divergence of E. coli and Salmonella typhimurium, most point mutations that occurred within each gene have been propagated among the gene family by conversions involving short domains, and that homogenization by conversions may not have affected the entire sequence of each gene. We show that the differences that exist between the different operons are ignored when sequences are obtained either after cloning of a single operon or directly from polymerase chain reaction (PCR) products. Direct sequencing of PCR products produces a mean sequence in which mutations present in the most variable domains become hidden. Cloning a single operon results in a sequence that differs from that of the other operons and of the mean sequence by several point mutations. For identification of unknown bacteria at the species level or below, a mean sequence or the sequence of a single nonidentified operon should therefore be avoided. Taking into account the seven operons and therefore mutations that accumulate in the most variable domains would perhaps increase tree resolution. However, if gene conversions that homogenize the rRNA multigene family are rare events, some nodes in phylogenetic trees will reflect these recombination events and these trees may therefore be gene trees rather than organismal trees.

[Acute granulomatous appendicitis. (Contribution to preventive appendectomy in acute ileitis)]. / L'appendicite acuta granulomatosa. (Contributo all'appendicectomia profilattica nell'ileita acuta).

Starting with one case of acute granulomatous appendicitis of their own observation, the authors review the scant literature on the subject (only 23 published cases to date) and advocate systematic appendicectomy in all isolated appendicular localizations of Crohn's disease. On the grounds that no post-appendicectomy fistulization has ever been reported in such patients, the authors recommend prophylactic appendicectomy also in the far more frequent cases of acute ileitis, to forestall the possibility of evolution into chronic Crohn's disease and the risk of missing a nongranulomatous acute appendicitis appearing with the same clinical symptoms.