Self-assembly in solution of a reversible comb-shaped supramolecular polymer

We report a single step synthesis of a polyisobutene with a bis-urea moiety in the middle of the chain. In low polarity solvents, this polymer self-assembles by hydrogen bonding to form a combshaped polymer with a central hydrogen bonded backbone and polyisobutene arms. The comb backbone can be reversibly broken, and consequently, its length can be tuned by changing the solvent, the concentration or the temperature. Moreover, we have proved that the bulkiness of the side-chains have a strong influence on both the self-assembly pattern and the length of the backbone. Finally, the density of arms can be reduced, by simply mixing with a low molar mass bis-urea

Rapid and sensitive PCR detection of Vibrio penaeicida, the putative etiological agent of Syndrome 93 in New Caledonia

Experimental infections of Penaeus (Litopenaeus) stylirostris were performed with a Vibrio penaeicida strain (AM101) isolated in New Caledonia from Syndrome 93 diseased shrimp. Cumulative mortalities resulting from intramuscular injection or immersion of shrimp in bacterial suspensions demonstrated high virulence for this bacterial strain and suggested that V. penaeicida could be the etiological agent of Syndrome 93. The median lethal dose (LD50) for AM101 was 1.3 x 104 CFU (colony forming units) ml-1 by immersion and less than 5 CFU shrimp-1 by intramuscular challenge, with mortality outbreaks at 48 and 22 h after challenge, respectively. A polymerase chain reaction (PCR) detection assay using a primer set designed from the 16S ribosomal RNA gene of V. penaeicida was developed. It gave an expected amplicon of approximately 310 bp in ethidium bromide-stained agarose gels. The specificity of these primers was assessed with different Vibrio species. Furthermore, DNA extracted by the ChelexTM method could be used to detect fewer than 20 cultured Vibrio cells in seawater or shrimp hemolymph by this assay. It appears to be a reliable screening method for detecting V. penaeicida in shrimp and from the aquatic environment

Genetic structure at different spatial scales in the pearl oyster (Pinctada margaritifera cumingii) in French Polynesian lagoons: beware of sampling strategy and genetic patchiness

International audienceIn order to study further the genetic structure of the pearl oyster Pinctada margaritifera in French Polynesia with a special consideration for the sampling scale, we analyzed or re-analyzed sets of data based on nuclear DNA markers obtained at different spatial scales. At a large scale (several 1,000 km), the remote Marquesas Islands were confirmed to be significantly differentiated from Tuamotu-Gambier and Society archipelagos, with a marked difference however for the two main islands that are different from each other. At a medium scale (several 10 to several 100 km), overall homogeneity was observed within and between these two archipelagos, with some exceptions. This could be attributed both to large-scale larval dispersal and to human-driven spat translocations due to pearl oyster cultivation. These results contrast with those observed (1) at a small scale (less than 10 km) in a lagoon heavily impacted by translocation and cultural practices, where significant genetic differentiation was detected among three laying beds, and (2) at a micro scale where we detected an important variability of the genetic composition of young spat recruited on artificial collectors. Such patterns could result from a high variance in the number of genitors at the origin of each cohort, or from pre- or post-settlement selection on linked loci. Altogether, our data support the hypothesis that under certain conditions populations of bivalves may exhibit patterns of chaotic genetic patchiness at local scale, in line with the increasing report of such patchiness in marine benthic organisms. This underlines the importance of sampling scale that should be rigorously defined depending on the questions to be answered. Nevertheless, a survey of about 80 articles dealing with population genetics of marine invertebrates showed that only 35% of those studies disclosed details about the sampling strategy (particularly the area explored). These results emphasize the need for cautious interpretation of patterns of genetic structure at medium scale when rigorous sampling strategies are not deployed

Evaluation de la variabilité génétique de P. stylirostris disponible en Nouvelle-Calédonie

Shrimp farming has been developed in New-Caledonia thanks to the domestication of P. stylirostris which was introduced from Mexico and Panama in several times between 1970 and 1980. In over than 25 generations the genetic variability initially available was eroded (by selection and drift) which is demonstrated by four microsatellites markers in this study where five populations of New-Caledonia are compared with a Tahitian population (population with low variability but known to be genetically improvable and a priori genetically close to the New-Caledonian populations) and with a wild Equatorial! population (a priori representative of the genetic variability of the species). In the six reared populations the allelic diversity and the heterozygosity level are low (1 to 3 alleles per locus instead of 14 to 25; 10% to 20% heterozygosity instead of 90%). In addition, the Tahitian and Caledonian strains have the same alleles, which suggests (i) that the loss of alleles occured during the common history of these populations at the beginning of their domestication and (ii) that a selective breeding program could generate in New Caledonia a significant (but limited) genetic improvement equivalent to the one obtained in Tahitian experiments. Nevertheless, the very low genetic variability of the New-Caledonian domesticated populations represents a risk to be unable to adapt to an environmental change (controlled or uncontrolled). The results of the present study demonstrate, on objective data, the usefulness of introducing genetic variability in New-Caledonia, but on the condition that it is correctly managed and that all the consequences in terms of risk management are integrated by the institutions in charge of the development of the shrimp farming industry.La crevetticulture s’est développée en Nouvelle-Calédonie grâce à la domestication de P. stylirostris, espèce introduite du Mexique et du Panama via Tahiti, en plusieurs fois entre 1970 et 1980. En plus de 25 générations, la variabilité génétique initialement disponible a subi une érosion (par sélection et par dérive) que quatre marqueurs microsatellites mettent en évidence dans cette étude dans laquelle cinq populations de Nouvelle-Calédonie sont comparées à une population de Tahiti (population peu variable mais reconnue comme génétiquement améliorable, et a priori proche de celle de NC) et à une population sauvage d’Equateur (a priori représentative de la variabilité génétique de l’espèce) : dans les 6 populations d’élevage, la diversité allélique et le niveau d’hétérozygotie s’avèrent très réduits (1 à 3 allèles par locus au lieu de 14 à 25 ; 10% à 20% d’hétérozygotie au lieu de 90%). En outre, les souches Tahitiennes et Calédoniennes disposent des mêmes allèles, ce qui suggère (i) que la perte d’allèles a eu lieu lors de l’histoire commune des ces populations au début de leur domestication et (ii) qu’un programme de sélection mené en Calédonie devrait permettre d’engendrer à terme un progrès significatif mais limité, équivalent à celui réalisé à Tahiti en expérimentation. Néanmoins, la très faible variabilité génétique du cheptel calédonien l’expose au risque de ne pas être capable de s’adapter à un éventuel changement (contrôlé ou non) des conditions d’élevage. Les résultats de cette étude permettent de confirmer, sur des bases objectives, l’utilité de l’introduction de sang neuf en Calédonie, à condition qu’il soit géré convenablement sur la durée et que les responsables du développement de la filière en intègrent toutes les implications en termes de gestion du risque

Flat band and Lifshitz transition in long-range-ordered supergraphene obtained by Erbium intercalation

International audienceWe report the observation of graphene doped up to the Lifshitz transition obtained solely by the intercalation of Erbium atoms. ARPES measurements show that a wide flat band is generated around the M point of the Brillouin zone. We propose that this is the effect of an induced spin-orbit coupling. Scanning Tunneling Microscopy (STM) experiments reveal a longrange ordered hexagonal superstructure: we argue that this reflects the ordering of the intercalated Er atoms acting as impurities. This system provides a playground to study the interaction between a magnetic order and a divergent density of states at the Fermi level