Modulation de l' expression des intégrines épithéliales par les lymphocytes des plaques de Peyer intestinales (conséquences sur les interactions entre épithélium, mésenchyme et Yersinia entéropathogènes)

PARIS7-Bibliothèque centrale (751132105) / SudocSudocFranceF

Influence of bacteria on the response of microalgae to contaminant mixtures

When microalgae are exposed to contaminants, the role of associated bacteria within the phycosphere, the microenvironment surrounding algal cells, remains largely unknown. The present study investigated the importance of algae-associated bacteria on the responses of microalgae growth to metallic and organic toxicant exposure. The effects of a polluted sediment elutriate, and of metal or pesticide mixtures at environmentally relevant concentrations (<10 μg L−1) were assessed on the growth of two microalgae strains: Isochrysis galbana, a prymnesiophyte, and Thalassiosira delicatula, a centric diatom. Both cultures were maintained as axenic or bacterized under similar conditions in batch cultures. In axenic conditions, the metal mixture addition at low concentrations alleviated limitation of growth by metals for T. delicatula relative to control, but inhibited I. galbana growth at highest concentration. In similar axenic conditions, both T. delicatula and I. galbana growth were negatively inhibited by pesticide mixture at concentrations as low as 10 ng L−1. The bacterial diversities associated with the two microalgae strains were significantly different (Bray–Curtis dissimilarity greater than 0.9) but their impact on microalgae growth was similar. The presence of bacteria reduced algal growth rate by ca. 50% compared to axenic cultures, whereas no significant effect of sediment elutriate, metal or pesticide mixtures was noticed on non-axenic algal growth rates. These results show that bacteria may have a negative effect on algal growth but can reduce pesticide toxicity or metal availability to algae

Poliovirus transcytosis through M-like cells.

During the digestive-tract phase of infection, poliovirus (PV) is found in the oropharynx and the intestine. It has been proposed that PV enters the organism by crossing M cells, which are scattered in the epithelial sheet covering lymphoid follicles of Peyer's patches. However, PV translocation through M cells has never been demonstrated. A model of M-like cells has been previously developed using monolayers of polarized Caco-2 enterocytes cocultured with lymphocytes isolated from Peyer's patches. In this model, lymphoepithelial interactions trigger the appearance of epithelial cells having morphological and functional characteristics of M cells. We have demonstrated efficient, temperature-dependent PV transcytosis in Caco-2 cell monolayers containing M-like cells. This experimental evidence is consistent with M cells serving as gateways allowing PV access to the basal face of enterocytes, the underlying immune follicle cells, and PV transport toward mesenteric lymph nodes

Impacts of chemical contamination on bacterio-phytoplankton coupling

Phytoplankton and bacterioplankton are the key components of the organic matter cycle in aquatic ecosystems, and their interactions can impact the transfer of carbon and ecosystem functioning. The aim of this work was to assess the consequences of chemical contamination on the coupling between phytoplankton and bacterioplankton in two contrasting marine coastal ecosystems: lagoon waters and offshore waters. Bacterial carbon demand was sustained by primary carbon production in the offshore situation, suggesting a tight coupling between both compartments. In contrast, in lagoon waters, due to a higher nutrient and organic matter availability, bacteria could rely on allochthonous carbon sources to sustain their carbon requirements, decreasing so the coupling between both compartments. Exposure to chemical contaminants, pesticides and metal trace elements, resulted in a significant inhibition of the metabolic activities (primary production and bacterial carbon demand) involved in the carbon cycle, especially in offshore waters during spring and fall, inducing a significant decrease of the coupling between primary producers and heterotrophs. This coupling loss was even more evident upon sediment resuspension for both ecosystems due to the important release of nutrients and organic matter. Resulting enrichment alleviated the toxic effects of contaminants as indicated by the stimulation of phytoplankton biomass and carbon production, and modified the composition of the phytoplankton community, impacting so the interactions between phytoplankton and bacterioplankton