Virulence, multiple infections and regulation of symbiotic population in the Wolbachia-Asobara tabida symbiosis.

The density and regulation of microbial populations are important factors in the success of symbiotic associations. High bacterial density may improve transmission to the next generation, but excessive replication could turn out to be costly to the host and result in higher virulence. Moreover, differences in virulence may also depend on the diversity of symbionts. Using the maternally transmitted symbiont Wolbachia, we investigated how bacterial density and diversity are regulated and influence virulence in host insects subject to multiple infection. The model we used was the wasp Asobara tabida that naturally harbors three different Wolbachia strains, of which two are facultative and induce cytoplasmic incompatibility, whereas the third is necessary for the host to achieve oogenesis. Using insect lines infected with different subsets of Wolbachia strains, we show that: (i) some traits of A. tabida are negatively affected by Wolbachia; (ii) the physiological cost increases with the number of co-infecting strains, which also corresponds to an increase in the total bacterial density; and (iii) the densities of the two facultative Wolbachia strains are independent of one another, whereas the obligatory strain is less abundant when it is alone, suggesting that there is some positive interaction with the other strains.

mtDNA polymorphisms in five French groups: importance of regional sampling.

According to classical markers, France has been reported to be regionally heterogeneous. Here, we propose to test the homogeneity of the French mitochondrial gene pool by analysing D-Loop and coding regions polymorphisms in 210 individuals stemming from five regions. The data set obtained was also used to test the ability of mitochondrial DNA to detect well historically established admixtures (admixtures between British/Irish people and native Breton people in our case). For these purposes, the sampling procedure was subject to special care, concerning the individuals' geographical origin and maternal pedigree. The mtDNA analysis revealed some regional specificities in haplogroup distribution, which is discussed in terms of successive settlements of France. Statistical analyses were conducted to investigate mtDNA diversity and structure within and between British, Irish and French groups. They tended to show affinities between Morbihan region and Britain plus Ireland. Furthermore, genetic evidences were in line with the fact that Morbihan region results from an admixture event, agreeing with historical evidences of successive migrations from Britain and Ireland into Brittany. These results also tended to outline the fact that two geographically very adjacent samples (Morbihan and Finistère), sharing a cultural and linguistic area, can present a distinct genetic pattern. Although mtDNA analyses were able to identify a historically reported admixture event, we point out here the high influence of the sampling procedure and representativeness over the migrations hypothesis. We also underline the importance of regional sampling for studies on the spread and/or origin of specific European haplogroups (here U5a1a and U8).

Multicenter quality control for the detection of hepatitis C virus RNA in seminal plasma specimens.

The discrepant results available in the literature about the presence of hepatitis C virus (HCV) RNA in seminal plasma of men chronically infected by this agent are related, at least in part, to the molecular techniques used and particularly to the wide range of protocols dedicated to RNA extraction. In order to evaluate these protocols and to standardize the method of detection of HCV RNA in this fluid, a panel of coded specimens was tested blindly in 12 French laboratories; it included 14 seminal plasma specimens and four water controls spiked with HCV RNA ranging from 10 to 20000 IU/ml and two HCV-negative seminal plasma specimens. The extraction step was performed according to methods using either silica beads (NucliSens [Organon Teknika S.A., Fresnes, France]; RNA viral kit [Qiagen, Courtaboeuf, France]) or guanidinium thiocyanate (Amplicor HCV assay; Roche Diagnostics, Meylan, France), preceded or not by a centrifugation of the seminal plasma. For the amplification step, all the laboratories performed the same reverse transcription-PCR technique (Amplicor HCV Cobas assay). The percentage of correct results ranged from 53.3 to 100, the poorest results being obtained when no centrifugation step preceded the Amplicor extraction protocol. The rate of correct results was significantly higher in laboratories using a preliminary centrifugation of the specimen (P = 0.034 by chi-square test). By contrast, the overall number of correct results was not correlated to the initial volume of sample used for the test. These results allowed us to validate standardized techniques adapted to the performance of this test on a routine basis, especially in men infected with HCV and involved in programs of medically assisted reproduction.