Insights on the trafficking and retro-translocation of glycosphingolipid-binding bacterial toxins

Some bacterial toxins and viruses have evolved the capacity to bind mammalian glycosphingolipids to gain access to the cell interior, where they can co-opt the endogenous mechanisms of cellular trafficking and protein translocation machinery to cause toxicity. Cholera toxin (CT) is one of the best-studied examples, and is the virulence factor responsible for massive secretory diarrhea seen in cholera. CT enters host cells by binding to monosialotetrahexosylganglioside (GM1 gangliosides) at the plasma membrane where it is transported retrograde through the trans-Golgi network (TGN) into the endoplasmic reticulum (ER). In the ER, a portion of CT, the CT-A1 polypeptide, is unfolded and then “retro-translocated” to the cytosol by hijacking components of the ER associated degradation pathway (ERAD) for misfolded proteins. CT-A1 rapidly refolds in the cytosol, thus avoiding degradation by the proteasome and inducing toxicity. Here, we highlight recent advances in our understanding of how the bacterial AB5 toxins induce disease. We highlight the molecular mechanisms by which these toxins use glycosphingolipid to traffic within cells, with special attention to how the cell senses and sorts the lipid receptors. We also discuss several new studies that address the mechanisms of toxin unfolding in the ER and the mechanisms of CT A1-chain retro-translocation to the cytosol

Data from: Habitat selection and the value of information in heterogenous landscapes

Despite the wide usage of the term information in evolutionary ecology, there is no general treatise between fitness (i.e., density-dependent population growth) and selection of the environment sensu lato. Here we (1) initiate the building of a quantitative framework with which to examine the relationship between information use in spatially heterogeneous landscapes and density-dependent population growth, and (2) illustrate its utility by applying the framework to an existing model of breeding habitat selection. We begin by linking information, as a process of narrowing choice, to population growth/fitness. Second, we define a measure of a population’s penalty of ignorance based on the Kullback-Leibler index that combines the contributions of resource selection (i.e., biased use of breeding sites) and density-dependent depletion. Third, we quantify the extent to which environmental heterogeneity (i.e., mean and variance within a landscape) constrains sustainable population growth of unbiased agents. We call this the heterogeneity-based fitness deficit, and combine this with population simulations to quantify the independent contribution of information-use strategies to the total population growth rate. We further capitalize on this example to highlight the interactive effects of information between ecological scales when fear affects individual fitness through phenotypic plasticity. Informed breeding habitat selection moderates the demographic cost of fear commensurate with density-dependent information use. Thus, future work should attempt to differentiate between phenotypic plasticity (i.e., acute fear) and demographic responses (i.e., chronic changes in population size). We conclude with a broader discussion of information in alternative contexts, and explore some evolutionary considerations for information use. We note how competition among individuals may constrain the information state among individuals, and the implications of this constraint under environmental change

Figure 3

Simulated data for determining p* for Figure

Massol-Debarre_notebook_20141007

<p>Mathematica notebook of the analytical calculations given in the paper.</p

The evolution of the competition– dispersal trade-off affects alpha-and beta-diversity in a heterogeneous metacommunity

International audienceDifference in dispersal ability is a key driver of species coexistence in metacommunities. However, the available frameworks for interpreting species diversity patterns in natura often overlook trade-offs and evolutionary constraints associated with dispersal. Here,we build a metacommunity model accounting for dispersal evolution and a competition-dispersal trade-off. Depending on the distribution of carrying capacities among communities, species dispersal values are distributed either around a single strategy (evolutionarily stable strategy, ESS), or around distinct strategies (evolutionary branching, EB). We show that limited dispersal generates spatial aggregation of dispersal traits in ESS and EB scenarios, and that the competition-dispersal trade-off strengthens the pattern in the EB scenario. Importantly, individuals in larger (respectively (resp.) smaller) communities tend to harbour lower (resp. higher) dispersal, especially under the EB scenario.We explore how dispersal evolution affects species diversity patterns by comparing those from our model to the predictions of a neutral metacommunity model. The most marked difference is detected under EB, with distinctive values of both alpha and beta diversity (e.g. the dissimilarity in species composition between small and large communities was significantly larger than neutral predictions). We conclude that, from an empirical perspective, jointly assessing community carrying capacity with species dispersal strategies should improve our understanding of diversity patterns in metacommunities

Preregistrations

The preregistration process at PCI Ecolog

Life history and eco-evolutionary dynamics in light of the gut microbiota

The recent emergence of powerful genomic tools, such as high-throughput genomics, transcriptomics and metabolomics, combined with the study of gnotobiotic animals, have revealed overwhelming impacts of gut microbiota on the host phenotype. In addition to provide their host with metabolic functions that are not encoded in its own genome, evidence is accumulating that gut symbionts affect host traits previously thought to be solely under host genetic control, such as development and behavior. Metagenomics and metatranscriptomics studies further revealed that gut microbial communities can rapidly respond to changes in host diet or environmental conditions through changes in their structural and functional profiles, thus representing an important source of metabolic flexibility and phenotypic plasticity for the host. Hence, gut microbes appear to be an important factor affecting host ecology and evolution which is, however, not accounted for in life-history theory, or in classic population genetics, ecological and eco-evolutionary models. In this forum, we shed new light on life history and eco-evolutionary dynamics by viewing these processes through the lens of host-microbiota interactions. We follow a three-level approach. First, current knowledge on the role of gut microbiota in host physiology and behavior points out that gut symbionts can be a crucial medium of life history strategies. Second, the particularity of the microbiota is based on its multilayered structure, composed of both a core microbiota, under host genetic and immune control, and a flexible pool of microbes modulated by the environment, which differ in constraints on their maintenance and in their contribution to host adaptation. Finally, gut symbionts can drive the ecological and evolutionary dynamics of their host through effects on individual, population, community and ecosystem levels. In conclusion, we highlight some future perspectives for integrative studies to test hypotheses on life history and eco-evolutionary dynamics in light of the gut microbiota.status: publishe

orchid-pollinator data

Interactions between orchid and pollinator species. Data from the literature. Full_database: database with 243 orchid species and 773 pollinator species. Reduced_database: database with 153 orchid species (i.e. orchid species for which phylogenetic data were available) and 726 pollinator specie