PPARγ ligands switched high fat diet-induced macrophage M2b polarization toward M2a thereby improving intestinal Candida elimination.

International audienceObesity is associated with a chronic low-grade inflammation that predisposes to insulin resistance and the development of type 2 diabetes. In this metabolic context, gastrointestinal (GI) candidiasis is common. We recently demonstrated that the PPARγ ligand rosiglitazone promotes the clearance of Candida albicans through the activation of alternative M2 macrophage polarization. Here, we evaluated the impact of high fat diet (HFD)-induced obesity and the effect of rosiglitazone (PPARγ ligand) or WY14643 (PPARα ligand) both on the phenotypic M1/M2 polarization of peritoneal and cecal tissue macrophages and on the outcome of GI candidiasis. We demonstrated that the peritoneal macrophages and the cell types present in the cecal tissue from HF fed mice present a M2b polarization (TNF-α(high), IL-10(high), MR, Dectin-1). Interestingly, rosiglitazone induces a phenotypic M2b-to-M2a (TNF-α(low), IL-10(low), MR(high), Dectin-1(high)) switch of peritoneal macrophages and of the cells present in the cecal tissue. The incapacity of WY14643 to switch this polarization toward M2a state, strongly suggests the specific involvement of PPARγ in this mechanism. We showed that in insulin resistant mice, M2b polarization of macrophages present on the site of infection is associated with an increased susceptibility to GI candidiasis, whereas M2a polarization after rosiglitazone treatment favours the GI fungal elimination independently of reduced blood glucose. In conclusion, our data demonstrate a dual benefit of PPARγ ligands because they promote mucosal defence mechanisms against GI candidiasis through M2a macrophage polarization while regulating blood glucose level

PPARγ Controls Dectin-1 Expression Required for Host Antifungal Defense against Candida albicans

We recently showed that IL-13 or peroxisome proliferator activated receptor γ (PPARγ) 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 PPARγ 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 PPARγ 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 PPARγ signaling pathway. These findings are consistent with a crucial role for PPARγ in the alternative activation of macrophages by Th2 cytokines. Altogether these data suggest that PPARγ 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

An “overlooked” habitat for thermophilic bacteria: the phyllosphere

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

Spatial dynamics for two different time periods.

<p>Diamond and full line correspond to samples collected in September whereas the squares and dashed lines correspond to samples collected at the same location in November. Circles correspond to background samples. White and black symbol corresponds to total bacteria and <i>S. rectivirgula</i> respectively.</p

Predicted <i>S. rectivirgula</i> concentration in 16S rRNA gene copies.g⁻¹ of <i>Pinus halepensis</i> needles.

<p>White spots correspond to the location of sampled trees. Narrow and thick black lines correspond to altitude and background level contour lines, respectively. The cross corresponds to the location of the composting plant. The wind map shows the frequency of no wind (0 to1.5 m.s⁻¹), light wind (1.5 to 4.5 m.s⁻¹), moderate wind (4.5 to 8 m.s⁻¹) and strong wind (up to 8 m.s⁻¹) in, respectively, white, light grey, medium grey and dark grey (Meteo France, <a href="http://www.meteofrance.com/" target="_blank">http://www.meteofrance.com/</a>).</p

Predicted total bacteria concentration in 16S rRNA gene copies.g⁻¹ of <i>Pinus halepensis</i> needles.

<p>White spots correspond to the location of sampled trees. Narrow black lines correspond to altitude. The cross corresponds to the location of the composting plant. The wind map shows the frequency of no wind (0 to1.5 m.s⁻¹), light wind (1.5 to 4.5 m.s⁻¹), moderate wind (4.5 to 8 m.s⁻¹) and strong wind (up to 8 m.s⁻¹) in, respectively, white, light grey, medium grey and dark grey (Meteo France, <a href="http://www.meteofrance.com/" target="_blank">http://www.meteofrance.com/</a>).</p

Concentration of 16S rRNA gene copies of <i>S. rectivirgula</i> and total bacteria on <i>Pinus halepensis</i> needles around a composting plan.

1<p>, <i>S. rectivirgula</i>;</p>2<p>, total bacteria expressed as log [copy per gram needle].</p><p>Concentration of 16S rRNA gene copies of <i>S. rectivirgula</i> and total bacteria on <i>Pinus halepensis</i> needles around a composting plan.</p

Bioremediation of fishpond effluent and production of microalgae for an oyster farm in an innovative recirculating integrated multi-trophic aquaculture system

Integrated multi-trophic aquaculture (IMTA) systems are a promising solution for sustainable aquaculture combining nutrient recycling with increased biomass production. An innovative land-based recirculating aquaculture system (RAS) was studied in France for a 60-day experiment. It combined a European sea bass (Dicentrarchus labrax) RAS with two other production systems: high rate algal ponds (HRAP) with natural marine polyspecific algal assemblages, and oysters in separate open tanks. The objective was the assessment of: 1) the efficiency and the stability of the microalgae bioremediation of the effluent from a fish RAS in spring and summer, 2) the abundance and the diversity patterns of the microalgae biomass for consumption in the oyster compartment of the IMTA. Silicate was added every week after the beginning of the experiment for maintaining a Si:N:P molar ratio of 10:5:1 in the HRAP to encourage the growth of diatoms. The HRAP have an overall removal efficiency of 98.6 ± 0.2% for NO3-N, 98.0 ± 0.4% for NO2-N, 97.3 ± 0.7% for NH4-N and 96.1 ± 0.6% for PO4-P, with removal rates of 335.8 ± 0.8, 23.6 ± 0.2, 30.9 ± 0.2, and 22.3 ± 0.2 mg m−2 d−1, respectively. The concentration of total suspended solid (TSS) and chlorophyll a (chl a) increased during the experiment and reached maximum values on day 46 (135.3 ± 34.7 mg TSS L−1 and 0.42 ± 0.03 mg chl a L−1) after which the microalgae collapsed due to a CO2 limitation (pH ca. 10). Sequencing analysis revealed that the microalgae community was dominated by Tetraselmis sp. from day 1 to day 16 (45.7% to 73.8% relative abundance). From day 30 to day 43 the culture was dominated by diatoms, Phaeodactylum sp. (83.4% to 98.1% relative abundance). Although the stable carbon isotope signatures confirmed that the microalgae were consumed, oysters' growth was limited in the RAS-IMTA, suggesting that oysters were under stress or not fed enough

Microbial successions during wastewater treatment start-up using microalgae

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