Prevalence of Epistasis in the Evolution of Influenza A Surface Proteins

The surface proteins of human influenza A viruses experience positive selection to escape both human immunity and, more recently, antiviral drug treatments. In bacteria and viruses, immune-escape and drug-resistant phenotypes often appear through a combination of several mutations that have epistatic effects on pathogen fitness. However, the extent and structure of epistasis in influenza viral proteins have not been systematically investigated. Here, we develop a novel statistical method to detect positive epistasis between pairs of sites in a protein, based on the observed temporal patterns of sequence evolution. The method rests on the simple idea that a substitution at one site should rapidly follow a substitution at another site if the sites are positively epistatic. We apply this method to the surface proteins hemagglutinin and neuraminidase of influenza A virus subtypes H3N2 and H1N1. Compared to a non-epistatic null distribution, we detect substantial amounts of epistasis and determine the identities of putatively epistatic pairs of sites. In particular, using sequence data alone, our method identifies epistatic interactions between specific sites in neuraminidase that have recently been demonstrated, in vitro, to confer resistance to the drug oseltamivir; these epistatic interactions are responsible for widespread drug resistance among H1N1 viruses circulating today. This experimental validation demonstrates the predictive power of our method to identify epistatic sites of importance for viral adaptation and public health. We conclude that epistasis plays a large role in shaping the molecular evolution of influenza viruses. In particular, sites with , which would normally not be identified as positively selected, can facilitate viral adaptation through epistatic interactions with their partner sites. The knowledge of specific interactions among sites in influenza proteins may help us to predict the course of antigenic evolution and, consequently, to select more appropriate vaccines and drugs

Presence of metals in biomass residues after pyrolysis

In contribution to research into renewable energy, pyrolysis tests are run to develop the process of pyrolysis of biomass allowing the production of Hydrogen. Various families of combustibles (oleaginous, lignocellulosics, and seeds) have been tested at different temperatures. The pyrolysis of biomass is hampered by technical problems such as the blockage of the furnace by tars. The residues are collected and treated in a solution of chloric and nitric acid, so that the mineral part is extracted and then analysed by ICP. The first results indicate the presence ofmetals: Ni, Mg, Zn, Mn, Fe... Various proposais for the use of these residues so as to avoid pollution due to their accumulation have been put forward. These ashes can be recombined with fuels, acting as catalysts to reduce the formation of tar and increase the production of hydrogen

Evidences of modifications in the size distribution of particles during a mercury depletion event at Kuujjuarapik/Whapmagoostui, Québec (Canada)

During a field experiment at Kuujjuarapik/Whapmagoustui (55°31N, 77°75W), Québec, we have pointed out modifications in the size distribution of particles during a Mercury Depletion Event (MDE). We observed an increase of atmospheric particles concentrations in the ambient air, correlated with depletions of ozone and atmospheric mercury. These increases were followed by a change in the size particles distribution. Assuming that the divalent mercury species formed during the MDE could be adsorbed onto particles, this is likely to contribute to higher deposition fluxes of oxidised mercury on the snow pack

Atmospheric particle evolution during a nighttime atmospheric mercury depletion event in sub-Arctic at Kuujjuarapik/Whapmagoostui, Québec, Canada

International audienceDuring a field experiment at Kuujjuarapik/Whapmagoostui (55.31°N, 77.75°W), Québec, we observed increases of concentrations of particles with diameters larger than 0.3 μm in the ambient air during a nighttime atmospheric mercury depletion event (AMDE). These increases were strongly correlated with decreases of ozone and atmospheric mercury, and we also observed a change in the particle size distribution during this AMDE. Assuming that these phenomena imply either a chemical link or an association through transport, we also studied the nature of this AMDE. We hypothesize that the observed AMDE was a result of an influx of already depleted air masses and that it was not a product of local chemical reactions

Study of the origin of atmospheric mercury depletion events recorded in Ny-Ålesund, Svalbard, spring 2003

International audienceAn international campaign involving six teams was organized in Ny-Ålesund, Svalbard, in order to understand better the origin of atmospheric mercury depletion events (AMDEs). Special emphasis was given to determining the source region of the observed events and the physical and chemical processes leading to AMDEs. Five AMDEs were recorded during a one-month field experiment (10 April-10 May, 2003). The different events presented various characteristics, especially in terms of mercury species formation, atmospheric particle variations and meteorological conditions. After careful examination of each event, we postulate that two were probably due to advection of already depleted air masses and three were a product of local or regional chemistry. The roles of different surfaces (frost flowers, snow, ice aerosol in clouds) involved in heterogeneous reactions leading to AMDEs are also discussed. We speculate that ice clouds may explain the particle variations observed during the three more local events

Etudes photochimiques des interactions de composes organiques volatils en milieux heterogenes

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