The acid−base and Zn sorption properties of three bacteria, Cupriavidus metallidurans CH34, Pseudomonas putida ATCC12633, and Escherichia coli K12DH5α, were investigated through an original combination of extended X-ray absorption fine structure (EXAFS) spectroscopy and equilibrium titration studies. Acid−base titration curves of the three strains were fitted with a model accounting for three conceptual reactive sites:  an acidic (carboxyl and/or phosphodiester), a neutral (phosphomonoester), and a basic (amine and/or hydroxyl) group. Calculated proton and Zn equilibrium constants and site densities compare with literature data. The nature of Zn binding sites was studied by EXAFS spectroscopy. Phosphoester, carboxyl, and unexpectedly sulfhydryl ligands were identified. Their proportions depended on Zn loading and bacterial strain and were consistent with the titration results. These findings were compared to the structure and site density of the major cell wall components. It appeared that the cumulated theoretical site density of these structures (<2 Zn nm-2) was much lower than the total site density of the investigated strains (16−56 Zn nm-2). These results suggest a dominant role of extracellular polymeric substances in Zn retention processes, although Zn binding to inner cell components cannot be excluded.

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Submerged aquatic plants are ecosystem engineers that are able to modify their habitat. However, 15 the role of patch size in the engineering capacity of aquatic plants has not yet been fully 16 investigated, while it could be essential for elucidating the consequences of plant presence. Our 17 objectives were to investigate the effects of patch size on plant-flow-sediment interactions in lotic 18 ecosystems and to determine whether these effects differed according to environmental 19 characteristics. 20We performed in situ measurements of velocity and grain size along natural patches of increasing 21 length (L) at two sites presenting different flow and sediment characteristics. Our results 22 ManuscriptClick here to access/download;Manuscript;Licci_et_al.docx indicated that a minimum patch size was needed to induce in-patch reduction of the time 23 averaged velocity component in the flow direction (i.e. streamwise velocity) and fine sediment 24 accumulation. Streamwise velocity decreased linearly with L independently of the site conditions. 25The sediment texture was instead dependent on site conditions: for the site characterized by 26 higher velocity and coarser sediment, the sediment grain size exponentially decreased with L, 27 reaching a minimum value at L ≥ 1.0 m, while for the site characterized by lower velocity and 28 finer sediment, it reached a minimum value already at L > 0.3 m. This study demonstrated that a 29 minimal patch size is required to trigger the ecosystem engineering capacity of aquatic plant 30 patches in lotic environments and that this capacity increases with patch length. Small patches 31 induce little to no modification of the physical habitat, with possible negative feedbacks for 32 plants. With increasing patch size, the habitat modifications induced by plants become more 33 important, potentially triggering positive feedbacks for plants. 34 35 ecosystems. These primary producers contribute to the functioning of the ecosystem, regulating 38 nutrient cycles, increasing habitat heterogeneity and serving as shelter and habitat for other 39 organisms (Carpenter and Lodge 1986; Cornacchia et al. 2019). As ecosystem engineers (sensu 40 Jones et al.1994), they play an essential role in aquatic ecosystems: rooted submerged plants 41 modify flow conditions and sedimentation patterns (Sand-Jensen 1998; Sand-Jensen and 42 Pedersen 1999), and some species are able to release oxygen into the substrate through their 43 roots, influencing the availability of nutrients and microbial activity and hence biogeochemical 44 processes in the substrate (Caffrey and Kemp 1992; Sand-Jensen et al. 1982; Soana and Bartoli 45 2013). In streams, aquatic plants commonly form mono-specific patches (Sand-Jensen and 47 Madsen 1992). The formation of patches is due to clonal growth, occurring mainly in the 48 downstream direction (Puijalon et al. 2008; Sand-Jensen and Madsen 1992). In addition to light 49 and nutrient availability, patch expansion also depends on flow conditions and sediment 50 characteristics, as...

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International audienceInfiltration basins are increasingly used in urban areas for flood protection, groundwater recharge and storm water disposal. However, their operation is often affected by clogging, leading to degraded infiltration. The aim of this work was to evaluate the respective influences of sediment deposition and biofilm biomass on the deterioration of hydraulic performances in two infiltration basins used for groundwater recharge. Samples were collected by coring in the two basins. Grain size distribution (with and without organic matter), bacterial and algal biomasses, and microbial activity were measured at three depths from the soil surface (0-1cm, 2-3cm and 10-14cm). In parallel, in situ single-ring infiltration tests were performed before and after removal of the top layer (0-1cm). The results showed considerably reduced permeability due to clogging of the top sedimentary layer in the two basins. The highest reduction of permeability was measured in the basin colonized by the largest algal biomass. The proportions of fine mineral particles (<63 mu m) were comparable in the two basins and could not explain their differences in saturated hydraulic conductivities. In addition, the relationships between biological and hydraulic parameters highlighted a threshold effect of algal biomass on the structure of the pore network, possibly explaining the decrease in infiltration. This original link between hydraulic and microbial characteristics suggests that algal biofilm growth had a major impact on the hydraulic performance of the infiltration basins. Copyright (c) 2013 John Wiley & Sons, Ltd