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Thermophilic microbes are present everywhere around us and their only known natural biotope is far away and most usually associated with geothermal energy. To answer this paradox, we explore the hypothesis that the phyllosphere (surface of leaves), due to its exposition to the sun, could well be a thermophilic habitat for microbes and thus a source of thermophilic microbes growing around 50°C – 60°C. To support this hypothesis, we reviewed the heat sources on earth and associated microbial habitats, as well as the difficult identification of thermophilic microbes. We further present an experiment to show the presence and activity of thermophilic bacteria in the phyllosphere. Leaves were collected from eleven tree species from five locations on three continents belonging to three different biomes. On fresh leaves, 16S rDNA sequencing reveals the presence of 0.2 to 7% of clearly identified thermophilic bacteria. Moreover, after incubation at 55°C under aerobic and anaerobic conditions, 16S rDNA sequencing reveals the presence of 4 to 99% of clearly identified thermophilic bacteria. The accumulation of observations provides coherence to our hypothesis and allows the emergence of a new vision of leaves as a thermophilic biotope. We then propose a life cycle of microbes belonging to the thermophilic biotope associated with leaf surfaces.

International audience; Intensive microalgae cultivation systems such as High Rate Algal Ponds (HRAPs) constitute a promising way to remove macropollutants from urban wastewater. However, two sanitary issues are associated with this treatment process: the presence of pathogens that have to be inactivated and the potential aerosolisation of a high concentration of microalgae that could affect human health. Concerning pathogenic bacteria, factors affecting their inactivation in HRAPs are still not well characterized. Two pilot scale HRAPs operating under different climates (Oceanic and Mediterranean) were monitored to evaluate their capacity to remove fecal indicator bacteria (FIB) and genera containing opportunistic pathogens. Traditional plating techniques, qPCR and Illumina sequencing were combined to determine bacterial concentrations. In both HRAPs, average log10 reduction values ranged between 1 and 2 Log for FIB. The clarification of wastewater and microalgal blooming induced a sharp decrease of the FIB and of genera containing opportunistic species (Acinetobacter, Aeromonas, Arcobacter, Streptococcus). At this time, important removal was recorded for culturable FIB (4.4 and 3 Log respectively, for thermotolerant coliforms and fecal streptococci), but not noticed when using qPCR. Differences between cultural and molecular results may be due to the presence of cells in a Viable But Non-Culturable State. After the blooming period, oxygen was the main factor affecting E. coli concentration, indicating that photooxidation may play a major role in the inactivation of this bacteria in HRAPs. At the air water interface of these open water treatment processes, bioaerosols are emitted that could represent a health problem. In dedicated lab-scale instrumented aerosolisation tanks (1 m3), the capacities of microalgae from natural consortia to become airborne were compared. Is was shown that cells of Chlorella are more prone to be aerosolised that cells of Scenedesmus-like species. The effect of water temperature, biomass concentration and the presence of surfactant on aerosolisation was evaluated.

International audience; Microalgae can be grown with wastewater in order to reduce the production cost, and recycle nitrogen and phosphorus from waste. Indeed, microalgal systems show great potential for extensive nutrient removal in wastewater treatment. High Rate Algal Ponds (HRAPs) however contain other organisms whose impact can be strong on the process dynamics. This work quantifies the role played by detritivores and algivores through a modelling approach. We present a model, in the framework of Activated Sludge Model, intended to describe the interaction between microalgae, zooplankton, and bacteria. The model is calibrated and tested with experimental data from a HARP fed with a WWTP. We show first that detritivores can have a positive role while they clarify the medium and provide light access to the algae stimulating micro-algae growth. The interaction microalgae/zoo-plankton is, however, much more complicated and grazing maintains a pressure on microalgae, and reduces the removal process efficiency.

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We recently showed that IL-13 or peroxisome proliferator activated receptor gamma (PPARgamma) ligands attenuate Candida albicans colonization of the gastrointestinal tract. Here, using a macrophage-specific Dectin-1 deficient mice model, we demonstrate that Dectin-1 is essential to control fungal gastrointestinal infection by PPARgamma ligands. We also show that the phagocytosis of yeast and the release of reactive oxygen intermediates in response to Candida albicans challenge are impaired in macrophages from Dectin-1 deficient mice treated with PPARgamma ligands or IL-13. Although the Mannose Receptor is not sufficient to trigger antifungal functions during the alternative activation of macrophages, our data establish the involvement of the Mannose Receptor in the initial recognition of non-opsonized Candida albicans by macrophages. We also demonstrate for the first time that the modulation of Dectin-1 expression by IL-13 involves the PPARgamma signaling pathway. These findings are consistent with a crucial role for PPARgamma in the alternative activation of macrophages by Th2 cytokines. Altogether these data suggest that PPARgamma ligands may be of therapeutic value in esophageal and gastrointestinal candidiasis in patients severely immunocompromised or with metabolic diseases in whom the prevalence of candidiasis is considerable.