Production rates and metabolism of short-chain fatty acids in the colon and whole body using stable isotopes

Short-chain fatty acids (SCFA; mainly acetate, propionate and butyrate) are largely produced in non-ruminants during the colonic bacterial fermentation of non-digestible carbohydrates. These intestinal exogenous SCFA pass in part through the splanchnic bed and reach the peripheral bloodstream, mixing with the endogenous circulating SCFA. The whole-body turnover of SCFA is thus composed of an endogenous peripheral turnover and an exogenous production that depends on dietary intake of non-digestible carbohydrates. In the present work methods were developed for determining the SCFA turnover in animals and in human subjects using stable isotopes. The original studies performed to determine endogenous and exogenous metabolism of SCFA in animals and in human subjects are summarised. Using intravenous infusion of 13C-labelled SCFA the whole-body turnover of acetate, propionate and butyrate was assessed in rats in a fasted state. The endogenous turnover of acetate and its oxidation were determined in healthy human subjects in the post-absorptive state, using intravenous infusion of[l-13C]acetate. Intragastric tracer infusions were performed to evaluate the splanchnic first-pass retention of acetate in adults. Finally, an original model was developed in healthy human subjects using intravenous infusion of[l-13C]acetate to determine in vivo the true colonic acetate production after ingestion of a non-digestible disaccharide. These present studies using stable isotopes provide the basis for a novel strategy to evaluate in vivo, in human subjects, the production of SCFA in the large intestin

Short-term responses and resistance of soil microbial community structure to elevated CO2 and N addition in grassland mesocosms

Nitrogen (N) addition is known to affect soil microbial communities, but the interactive effects of N addition with otherdrivers of global change remain unclear. The impacts of multiple global changes on the structure of microbial communities may be mediated by specific microbial groups with different life-history strategies. Here, we investigated the combined effects of elevated CO2 and N addition on soil microbial communities using PLFA profiling in a short-term grassland mesocosm experiment. We also examined the linkages between the relative abundance of r- and K-strategist microorganisms and resistance of the microbial community structure to experimental treatments. N addition had a significant effect on microbial community structure, likely driven by concurrent increases in plant biomass and in soil labile C and N. In contrast, microbial community structure did not change under elevated CO2 or show significant CO2 × N interactions. Resistance of soil microbial community structure decreased with increasing fungal/bacterial ratio, but showed a positive relationship with the Gram-positive/Gram-negative bacterial ratio. Our findings suggest that the Grampositive/ Gram-negative bacteria ratio may be a useful indicator of microbial community resistance and that K-strategist abundance may play a role in the short-term stability of microbial communities under global change

Habitat constraints on the functional significance of soil microbial communities

Habitat constraints on the functional significance of soil microbial communities. EGU 2017, European Geophysical Union General Assembly 201

Pavement Design for Curved Road Sections: Fatigue Performance of Interfaces and Longitudinal Top-down Cracking in Multilayered Pavements

International audienceThis paper focuses on damage processes other than the main one observed and studied in pavement design. Previous research has targeted the experimental fatigue performance of tack coats. The French Pavement Design method has been chosen herein to illustrate how interface fatigue performance can lead to improved design, especially when pavements are subjected to repeated horizontal loadings. In a curved pavement section, longitudinal top-down cracking is observed, and this damage process may also be taken into account during the design approach. A 3D finite element model has been derived to assess pavement lifetime. In conclusion, it is proposed to include the fatigue performance of interfaces when designing pavements with horizontal loadings and thin surface layers

Experimental investigation of tack coat fatigue performance: Towards an improved lifetime assessment of pavement structure interfaces

International audienceThis paper focuses on investigating the bonding fatigue performance between two asphalt concrete (AC) layers. For purposes of this experimental campaign, a customised double shear testing device was designed. Two interface conditions have been analysed herein: with and without a tack coat. Moreover, the corresponding fatigue behaviour has been analysed at two temperatures: 10 °C and 20 °C. As expected, the absence of a tack coat leads to a decrease in bonding fatigue performance. Since fatigue tests are highly time-consuming, a method that allows predicting the conventional interface fatigue law from accelerated shear fatigue tests has been proposed. Other novel findings on interface fatigue behaviourwill also be discussed. In addition to these fatigue results, an interface failure model is proposed to evaluate the interface lifetime. Incorporating interface fatigue performance into pavement analysis proves to be a key parameter in describing in situ pavement conditions and assessing pavement durability

Adaptive SLAM with synthetic stereo dataset generation for real-time dense 3D reconstruction

International audienceIn robotic mapping and navigation, of prime importance today with the trend for autonomous cars, simultaneous localization and mapping (SLAM) algorithms often use stereo vision to extract 3D information of the surrounding world. Whereas the number of creative methods for stereo-based SLAM is continuously increasing, the variety of datasets is relatively poor and the size of their contents relatively small. This size issue is increasingly problematic, with the recent explosion of deep learning based approaches, several methods require an important amount of data. Those multiple techniques contribute to enhance the precision of both localization estimation and mapping estimation to a point where the accuracy of the sensors used to get the ground truth might be questioned. Finally, because today most of these technologies are embedded on on-board systems, the power consumption and real-time constraints turn to be key requirements. Our contribution is twofold: we propose an adaptive SLAM method that reduces the number of processed frame with minimum impact error, and we make available a synthetic flexible stereo dataset with absolute ground truth, which allows to run new benchmarks for visual odometry challenges. This dataset is available online at http://alastor.labri.fr/

A graph theory-based multi-scale analysis of hierarchical cascade in molecular clouds : Application to the NGC 2264 region

The spatial properties of small star-clusters suggest that they may originate from a fragmentation cascade of the cloud for which there might be traces up to a few dozen of kAU. Our goal is to investigate the multi-scale spatial structure of gas clumps, to probe the existence of a hierarchical cascade and to evaluate its possible link with star production in terms of multiplicity. From the Herschel emission maps of NGC 2264, clumps are extracted using getsf software at each of their associated spatial resolution, respectively [8.4, 13.5, 18.2, 24.9, 36.3]". Using the spatial distribution of these clumps and the class 0/I Young Stellar Object (YSO) from Spitzer data, we develop a graph-theoretic analysis to represent the multi-scale structure of the cloud as a connected network. From this network, we derive three classes of multi-scale structure in NGC 2264 depending on the number of nodes produced at the deepest level: hierarchical, linear and isolated. The structure class is strongly correlated with the column density $N_{\rm H_2}$ since the hierarchical ones dominate the regions whose N$_{\rm H_2} > 6 \times 10^{22}$cm$^{-2}$. Although the latter are in minority, they contain half of the class 0/I YSOs proving that they are highly efficient in producing stars. We define a novel statistical metric, the fractality coefficient F that measure the fractal index describing the scale-free process of the cascade. For NGC 2264, we estimate F = 1.45$\pm$0.12. However, a single fractal index fails to fully describe a scale-free process since the hierarchical cascade starts at a 13 kAU characteristic spatial scale. Our novel methodology allows us to correlate YSOs with their multi-scale gaseous environment. This hierarchical cascade that drives efficient star formation is suspected to be both hierarchical and rooted by the larger-scale gas environment up to 13 kAU

Chicory increases acetate turnover, but not propionate and butyrate peripheral turnovers in rats

Chicory roots are rich in inulin that is degraded into SCFA in the caecum and colon. Whole-body SCFA metabolism was investigated in rats during food deprivation and postprandial states. After 22h of food deprivation, sixteen rats received an IV injection of radioactive 14C-labelled SCFA. The volume of distribution and the fractional clearance rate of SCFA were 0·25-0·27 litres/kg and 5·4-5·9%/min, respectively. The half-life in the first extracellular rapidly decaying compartment was between 0·9 and 1·4min. After 22h of food deprivation, another seventeen rats received a primed continuous IV infusion of 13C-labelled SCFA for 2h. Isotope enrichment (13C) of SCFA was determined in peripheral arterial blood by MS. Peripheral acetate, propionate and butyrate turnover rates were 29, 4 and 0·3μmol/kg per min respectively. Following 4 weeks of treatment with chicory root or control diets, eighteen fed rats received a primed continuous IV infusion of 13C-labelled SCFA for 2h. Intestinal degradation of dietary chicory lowered caecal pH, enhanced caecal and colonic weights, caecal SCFA concentrations and breath H2.The diet with chicory supplementation enhanced peripheral acetate turnover by 25% (P=0·017) concomitant with an increase in plasma acetate concentration. There were no changes in propionate or butyrate turnovers. In conclusion, by setting up a multi-tracer approach to simultaneously assess the turnovers of acetate, propionate and butyrate it was demonstrated that a chronic chicory-rich diet significantly increases peripheral acetate turnover but not that of propionate or butyrate in rat