Between but not within species variation in the distribution of fitness effects

New mutations provide the raw material for evolution and adaptation. The distribution of fitness effects (DFE) describes the spectrum of effects of new mutations that can occur along a genome, and is therefore of vital interest in evolutionary biology. Recent work has uncovered striking similarities in the DFE between closely related species, prompting us to ask whether there is variation in the DFE among populations of the same species, or among species with different degrees of divergence, i.e., whether there is variation in the DFE at different levels of evolution. Using exome capture data from six tree species sampled across Europe we characterised the DFE for multiple species, and for each species, multiple populations, and investigated the factors potentially influencing the DFE, such as demography, population divergence and genetic background. We find statistical support for there being variation in the DFE at the species level, even among relatively closely related species. However, we find very little difference at the population level, suggesting that differences in the DFE are primarily driven by deep features of species biology, and that evolutionarily recent events, such as demographic changes and local adaptation, have little impact

Aluminum Methyl and Chloro Complexes Bearing Monoanionic Aminephenolate Ligands: Synthesis, Characterization, and Use in Polymerizations

A series of aluminum methyl and chloride complexes bearing 2(N-piperazinyl-N′-methyl)-2-methylene-4-R′-6-R-phenolate or 2(N-morpholinyl)-2-methylene-4-R′-6-R-phenolate ([ONER1,R2]-) {[R1 = tBu, R2 = Me, E = NMe (L1); R1= R2 = tBu, E = NMe (L2); R1 = R2 = tBu, E = O (L3)} ligands were synthesized and characterized through elemental analysis, 1H, 13C{1H}, and 27Al NMR spectroscopy, and X-ray crystallography. Reactions of AlMe3 with two equivalents of L1H-L3H gave {[ONER1,R2]2AlMe} (1–3), while reaction of Et2AlCl with two equivalents of L1H and L3H afforded {[ONER1,R2]2AlCl} (4 and 5) as monometallic complexes. The catalytic activity of complexes 1–3 toward ring-opening polymerization (ROP) of ε-caprolactone was assessed. These complexes are more active than analogous Zn complexes for this reaction but less active than the Zn analogues for ROP of rac-lactide. Characteristics of the polymer as well as polymerization kinetics and mechanism were studied. Polymer end-group analyses were achieved using 1H NMR spectroscopy and MALDI-TOF MS. Eyring analyses were performed, and the activation energies for the reactions were determined, which were significantly lower for 1 and 2 compared with 3. This could be for several reasons: (1) the methylamine (NMe) group of 1 and 2, which is a stronger base than the ether (O) group of 3, might activate the incoming monomer via noncovalent interactions, and/or (2) the ether group is able to temporarily coordinate to the metal center and blocks the vacant coordination site toward incoming monomer, while the amine cannot do this. Preliminary studies using 4 and 5 toward copolymerization of cyclohexene oxide with carbon dioxide have been performed. 4 was inactive and 5 afforded polyether carbonate (66.7% epoxide conversion, polymer contains 54.0% carbonate linkages)

CRISPR is an optimal target for the design of specific PCR assays for salmonella enterica serotypes Typhi and Paratyphi A

International audienceBACKGROUND:Serotype-specific PCR assays targeting Salmonella enterica serotypes Typhi and Paratyphi A, the causal agents of typhoid and paratyphoid fevers, are required to accelerate formal diagnosis and to overcome the lack of typing sera and, in some situations, the need for culture. However, the sensitivity and specificity of such assays must be demonstrated on large collections of strains representative of the targeted serotypes and all other bacterial populations producing similar clinical symptoms.METHODOLOGY:Using a new family of repeated DNA sequences, CRISPR (clustered regularly interspaced short palindromic repeats), as a serotype-specific target, we developed a conventional multiplex PCR assay for the detection and differentiation of serotypes Typhi and Paratyphi A from cultured isolates. We also developed EvaGreen-based real-time singleplex PCR assays with the same two sets of primers.PRINCIPAL FINDINGS:We achieved 100% sensitivity and specificity for each protocol after validation of the assays on 188 serotype Typhi and 74 serotype Paratyphi A strains from diverse genetic groups, geographic origins and time periods and on 70 strains of bacteria frequently encountered in bloodstream infections, including 29 other Salmonella serotypes and 42 strains from 38 other bacterial species.CONCLUSIONS:The performance and convenience of our serotype-specific PCR assays should facilitate the rapid and accurate identification of these two major serotypes in a large range of clinical and public health laboratories with access to PCR technology. These assays were developed for use with DNA from cultured isolates, but with modifications to the assay, the CRISPR targets could be used in the development of assays for use with clinical and other samples