Linkage disequilibrium between the four most common cystic fibrosis mutations and microsatellite haplotypes in the Celtic population of Brittany

Microsatellite haplotypes were determined for 117 chromosomes carrying the four most frequent mutations in the cystic fibrosis (CF) gene identified in the Breton population of Celtic origin, as well as for 83 normal chromosomes (noncarriers of a CF mutation). Each of the three non-ΔF508 mutations was associated with a single haplotype: 1078delT with 16-31-13, G551D with 16-7-17, and W846X with 16-32-13. Although these results suggest identity-by-descent for each mutation, recurrent mutations, although unlikely, could not be completely ruled out. The four most frequent haplotypes on normal chromosomes and the three most frequent haplotypes on ΔF508 chromosomes are the same as those found in Ireland, Spain, and Italy. This suggests that some haplotypes, associated or not with the ΔF508 mutation, were present in an ancestral population from which all four populations descended. Received: 27 November 1995 / Revised: 1 February 1996     

Challenges and ways forward in pesticide emission and toxicity characterization modeling for tropical conditions

The International Journal of Life Cycle Assessment - In tropical cropping systems, pesticides are extensively used to fight pests and ensure high crop yields. However, pesticide use also leads to...     

Correction to: Challenges and ways forward in pesticide emission and toxicity characterization modeling for tropical conditions

The International Journal of Life Cycle Assessment - © The Author(s) 2019     

Density of deer in relation to the prevalence of Borrelia burgdorferi s.1. in Ixodes ricinus nymphs in Rambouillet forest, France

The Rambouillet Forest, a Lyme disease-endemic area near Paris, France, was surveyed from September 1994 to October 1995 to determine the risk periods and zones for humans. Firstly, during the period of Ixodes ricinus activity, abundance of nymphs is greater in spring than in autumn. Secondly, we observed significant variation in nymphal abundance between zones according to the density of cervids. The polymerase chain reaction (PCR) was used to detect DNA of Borrelia burgdorferi sensu lato in 461 unfed nymphs. DNA was detected in 38 nymphs (8.2%). By genospecific PCR based on the OspA gene, we detected the three pathogenic spirochetes with occurrences of 10.3, 31.1 and 58.6 for B. burgdorferi s.s., Borrelia garinii and Borrelia afzelii, respectively, indicating that B. afzelii is probably the main Borrelia species in the Rambouillet Forest. Finally, 11.5% of positive nymphs exhibited a double infection. Infection rates of I. ricinus nymphs by B. burgdorferi s.l. were not significantly different throughout the year for a given area, indicating that the risk periods of acquiring Lyme disease are mainly linked to nymph activity and correspond to spring and autumn. Likewise infection rates of nymphs were not significantly different between zones with a high density of deer (more than 100 animals per 100 ha) and zones with lower deer density (less than 20 animals per 100 ha). In addition to the role of deer as an amplifier of tick populations, these data indicate that zones with a high density of cervids should be considered as higher risk areas. © Rapid Science Ltd. 1998     

Catalytic activity studies of some copper(II)-histidine-containing dipeptide complexes on aqueous superoxide ion dismutation

The reactivity of histidine-containing copper(II)-dipeptide complexes toward O₂^? produced by the pulse radiolysis technique was investigated. Whereas the His-X-Cu^2? complexes (X = Phe, Ala, Val, Tyr) display a relatively high superoxide dismutase (SOD) activity, that of the Ala-His-Cu²⁺ complex is very low and Val-His-Cu²⁺ as well as Phe-His-Cu²⁺ are ineffective. This difference in behavior can be explained by the fact that the Cu ion is not chelated in the same way in the different complexes, as shown by stability constant determination and other spectral studies. This allows one to conclude that in His-X-Cu²⁺, the dipeptide coordinates to the metal ion by only two nitrogens, whereas in X-His-Cu²⁺ it behaves as a tridentate ligand with three nitrogen atoms bound to the metal.     

Experimental evolution of nodule intracellular infection in legume symbionts

Soil bacteria known as rhizobia are able to establish an endosymbiosis with legumes that takes place in neoformed nodules in which intracellularly hosted bacteria fix nitrogen. Intracellular accommodation that facilitates nutrient exchange between the two partners and protects bacteria from plant defense reactions has been a major evolutionary step towards mutualism. Yet the forces that drove the selection of the late event of intracellular infection during rhizobium evolution are unknown. To address this question, we took advantage of the previous conversion of the plant pathogen Ralstonia solanacearum into a legume-nodulating bacterium that infected nodules only extracellularly. We experimentally evolved this draft rhizobium into intracellular endosymbionts using serial cycles of legume-bacterium cocultures. The three derived lineages rapidly gained intracellular infection capacity, revealing that the legume is a highly selective environment for the evolution of this trait. From genome resequencing, we identified in each lineage a mutation responsible for the extracellular–intracellular transition. All three mutations target virulence regulators, strongly suggesting that several virulence-associated functions interfere with intracellular infection. We provide evidence that the adaptive mutations were selected for their positive effect on nodulation. Moreover, we showed that inactivation of the type three secretion system of R. solanacearum that initially allowed the ancestral draft rhizobium to nodulate, was also required to permit intracellular infection, suggesting a similar checkpoint for bacterial invasion at the early nodulation/root infection and late nodule cell entry levels. We discuss our findings with respect to the spread and maintenance of intracellular infection in rhizobial lineages during evolutionary times.