Whole genome sequences of two Salmonella Dublin strains harbour viaA, viaB and ompB loci of the Vi antigen

Here we report the genome sequence of two Salmonella enterica serovar Dublin, 03EB8736SAL and 03EB8994SAL, isolated from raw milk cheese and filter of milk respectively. Analysis of draft genomes of the two isolates reveals the presence of viaA, viaB and ompB loci of the Vi capsular polysaccharide antigen (Vi antigen)

Halogenase Genes in Nonribosomal Peptide Synthetase Gene Clusters of Microcystis (Cyanobacteria): Sporadic Distribution and Evolution

Cyanobacteria of the genus Microcystis are known to produce secondary metabolites of large structural diversity by nonribosomal peptide synthetase (NRPS) pathways. For a number of such compounds, halogenated congeners have been reported along with nonhalogenated ones. In the present study, chlorinated cyanopeptolin- and/or aeruginosin-type peptides were detected by mass spectrometry in 17 out of 28 axenic strains of Microcystis. In these strains, a halogenase gene was identified between 2 genes coding for NRPS modules in respective gene clusters, whereas it was consistently absent when the strains produced only nonchlorinated corresponding congeners. Nucleotide sequences were obtained for 12 complete halogenase genes and 14 intermodule regions of gene clusters lacking a halogenase gene or containing only fragments of it. When a halogenase gene was found absent, a specific, identical excision pattern was observed for both synthetase gene clusters in most strains. A phylogenetic analysis including other bacterial halogenases showed that the NRPS-related halogenases of Microcystis form a monophyletic group divided into 2 subgroups, corresponding to either the cyanopeptolin or the aeruginosin peptide synthetases. The distribution of these peptide synthetase gene clusters, among the tested Microcystis strains, was found in relative agreement with their phylogeny reconstructed from 16S–23S rDNA intergenic spacer sequences, whereas the distribution of the associated halogenase genes appears to be sporadic. The presented data suggest that in cyanobacteria these prevalent halogenase genes originated from an ancient horizontal gene transfer followed by duplication in the cyanobacterial lineage. We propose an evolutionary scenario implying repeated gene losses to explain the distribution of halogenase genes in 2 NRPS gene clusters that subsequently defines the seemingly erratic production of halogenated and nonhalogenated aeruginosins and cyanopeptolins among Microcystis strains

Lack of Phylogeographic Structure in the Freshwater Cyanobacterium Microcystis aeruginosa Suggests Global Dispersal

Background : Free-living microorganisms have long been assumed to have ubiquitous distributions with little biogeographic signature because they typically exhibit high dispersal potential and large population sizes. However, molecular data provide contrasting results and it is far from clear to what extent dispersal limitation determines geographic structuring of microbial populations. We aimed to determine biogeographical patterns of the bloom-forming freshwater cyanobacterium Microcystis aeruginosa. Being widely distributed on a global scale but patchily on a regional scale, this prokaryote is an ideal model organism to study microbial dispersal and biogeography. Methodology/Principal Findings : The phylogeography of M. aeruginosa was studied based on a dataset of 311 rDNA internal transcribed spacer (ITS) sequences sampled from six continents. Richness of ITS sequences was high (239 ITS types were detected). Genetic divergence among ITS types averaged 4% (maximum pairwise divergence was 13%). Preliminary analyses revealed nearly completely unresolved phylogenetic relationships and a lack of genetic structure among all sequences due to extensive homoplasy at multiple hypervariable sites. After correcting for this, still no clear phylogeographic structure was detected, and no pattern of isolation by distance was found on a global scale. Concomitantly, genetic differentiation among continents was marginal, whereas variation within continents was high and was mostly shared with all other continents. Similarly, no genetic structure across climate zones was detected. Conclusions/Significance : The high overall diversity and wide global distribution of common ITS types in combination with the lack of phylogeographic structure suggest that intercontinental dispersal of M. aeruginosa ITS types is not rare, and that this species might have a truly cosmopolitan distribution

24 - Distribution spatiale journalière du corégone lors d'un bloom de Planktothrix rubescens : une voie directe d'accumulation de microcystine

National audienceDepuis les années 90, le lac du Bourget connaît des efflorescences de la cyanobactérie Planktothrix rubescens. Cette espèce est capable de produire une hépatotoxine, la microcystine. Dans de nombreux milieux, lors d’épisodes de blooms, cette toxine est retrouvée dans divers organes de nombreuses espèces de poissons, induisant des dommages physiologiques notables et des mortalités parfois importantes en cas de sénescence du bloom. Toutefois, les données sur l'exposition des poissons à cette toxine en milieu naturel sont peu nombreuses. La comparaison de la distribution spatiale de P. rubescens et des espèces piscicoles exploitées sur le lac (Perches et Corégones) est donc nécessaire pour déterminer si les poissons évitent ou se concentrent dans les zones touchées par les cyanobactéries. De Juin à Novembre 2009, les distributions spatiales diurnes de P. rubescens et des corégones (Coregonus lavaretus) ont été suivies à l’aide d’une sonde BBE et d’un échosondeur. Ainsi, les distributions verticales et horizontales ont été comparées pour toutes les dates d’échantillonnages. Les résultats montrent que les abondances de P. rubescens ont été maximales entre la fin du mois de juillet et le début du mois de Septembre. Durant cette période, P. rubescens se stratifie verticalement dans la colonne d’eau avec un maximum d’abondance situé entre 14 et 22 mètres en fonction des stations d’échantillonnages. A l’échelle horizontale, la distribution de P .rubescens est hétérogène sur l’ensemble du lac. Les données sur la distribution du corégone indiquent que pendant la journée, cette espèce est présente dans la couche d’eau située entre 15 et 30 mètres, couche d’eau où était également présent le pic de P. rubescens. De plus, le corégone ne semble ni éviter, ni au contraire être plus présent dans les zones de fortes abondances en P. rubescens. Les efflorescences de P. rubescens, aux concentrations observées, n’exercent donc pas de pression sur le schéma de répartition spatiale du corégone Par ailleurs, des filaments de P. rubescens ont été trouvés dans les contenus stomacaux de plusieurs corégones capturés par la pêche professionnelle et des toxines ont été mesurées dans divers organes. Ces derniers résultats indiquent qu’en raison du contact direct entre les poissons et les algues, la toxine peut facilement être accumulée dans le corégone par cette ingestion directe de filaments de P. rubescens, et donc conduire à des risques physiologiques pour cette espèce

Bacillus cereus-induced food-borne outbreaks in France, 2007 to 2014: epidemiology and genetic characterisation

The aim of this study was to identify and characterise Bacillus cereus from a unique national collection of 564 strains associated with 140 strong-evidence food-borne outbreaks (FBOs) occurring in France during 2007 to 2014. Starchy food and vegetables were the most frequent food vehicles identified; 747 of 911 human cases occurred in institutional catering contexts. Incubation period was significantly shorter for emetic strains compared with diarrhoeal strains A sub-panel of 149 strains strictly associated to 74 FBOs and selected on Coliphage M13-PCR pattern, was studied for detection of the genes encoding cereulide, diarrhoeic toxins (Nhe, Hbl, CytK1 and CytK2) and haemolysin (HlyII), as well as panC phylogenetic classification. This clustered the strains into 12 genetic signatures (GSs) highlighting the virulence potential of each strain. GS1 (nhe genes only) and GS2 (nhe, hbl and cytK2), were the most prevalent GS and may have a large impact on human health as they were present in 28% and 31% of FBOs, respectively. Our study provides a convenient molecular scheme for characterisation of B. cereus strains responsible for FBOs in order to improve the monitoring and investigation of B. cereus-induced FBOs, assess emerging clusters and diversity of strains