Design of infrared optical absorber using silver nanorings array made by a top-down process.

This paper presents the numerical simulation and fabrication of a metasurface composed of silver nanorings with a split-ring gap. These nanostructures can exhibit optically-induced magnetic responses with unique possibilities to control absorption at optical frequencies. The absorption coefficient of the silver nanoring was optimized by performing a parametric study with Finite Difference Time Domain (FDTD) simulations. The absorption and scattering cross sections of the nanostructures are numerically calculated to assess the impact of the inner and outer radii, the thickness and the split-ring gap of one nanoring, as well as the periodicity factor for a group of four nanorings. This showed full control on resonance peaks and absorption enhancement in the near infrared spectral range. The experimental fabrication of this metasurface made of an array of silver nanorings is achieved by e-beam lithography and metallization. Optical characterizations are then carried out and compared to the numerical simulations. In contrast to usual microwave split-ring resonator metasurfaces reported in literature, the present study shows both the realization by a top-down process and modelling performed in the infrared frequency range.

Early skeletal colonization of the coral holobiont by the microboring Ulvophyceae Ostreobium sp.

Ostreobium sp. (Bryopsidales, Ulvophyceae) is a major microboring alga involved in tropical reef dissolution, with a proposed symbiotic lifestyle in living corals. However, its diversity and colonization dynamics in host's early life stages remained unknown. Here, we mapped microborer distribution and abundance in skeletons of the branching coral Pocillopora damicornis from the onset of calcification in primary polyps (7 days) to budding juvenile colonies (1 and 3 months) growing on carbonate and non-carbonate substrates pre-colonized by natural biofilms, and compared them to adult colonies (in aquarium settings). Primary polyps were surprisingly already colonized by microboring filaments and their level of invasion depended on the nature of settlement substrate and the extent of its pre-colonization by microborers. Growth of early coral recruits was unaffected even when microborers were in close vicinity to the polyp tissue. In addition to morphotype observations, chloroplast-encoded rbcL gene sequence analyses revealed nine new Ostreobium clades (OTU99%) in Pocillopora coral. Recruits and adults shared one dominant rbcL clade, undetected in larvae, but also present in aquarium seawater, carbonate and non-carbonate settlement substrates, and in corals from reef settings. Our results show a substratum-dependent colonization by Ostreobium clades, and indicate horizontal transmission of Ostreobium-coral associations.

Integration of the colicin A pore-forming domain into the cytoplasmic membrane of Escherichia coli.

The pore-forming domain of colicin A (pfColA) fused to a prokaryotic signal peptide (sp-pfColA) inserted into the inner membrane of Escherichia coli and apparently formed a functional channel, when generated in vivo. We investigated pfColA functional activity in vivo by the PhoA gene fusion approach, combined with cell fractionation and protease susceptibility experiments. Alkaline phosphatase was fused to the carboxy-terminal end of each of the ten alpha-helices of sp-pfColA to form a series of differently sized fusion proteins. We suggest that the alpha-helices anchoring pfColA in the membrane are first translocated into the periplasm. We identify two domains that anchor pfColA to the membrane in vivo: domain 1, extending from helix 1 to helix 8, which contains the voltage-responsive segment and domain 2 consisting of the hydrophobic helices 8 and 9. These two domains function independently. Fusion proteins with a mutation inactivating the voltage-responsive segment or with a domain 1 lacking helix 8 were peripherally associated with the outside of the inner membrane, and were therefore digested by proteases added to spheroplasts. In contrast, fusion proteins with a functional domain 1 were protected from proteases, suggesting as expected that most of domain 1 is inserted into the membrane or is indeed translocated to the cytoplasm during pfColA channel opening.

The C-terminal half of the colicin A pore-forming domain is active in vivo and in vitro.

The pore-forming domain of colicin A (pfColA) fused to a prokaryotic signal peptide (sp-pfColA) is transported across and inserts into the inner membrane of Escherichia coli from the periplasmic side and forms a functional channel. The soluble structure of pfColA consists of a ten-helix bundle containing a hydrophobic helical hairpin. Here, we generated a series of mutants in which an increasing number of sp-pfColA alpha-helices was deleted. These peptides were tested for their ability to form ion channels in vivo and in vitro. We found that the shortest sp-pfColA mutant protein that killed Escherichia coli was composed of the five last alpha-helices of sp-pfColA, whereas the shortest peptide that formed a channel in planar lipid bilayer membranes similar to that of intact pfColA was the protein composed of the last six alpha-helices. The peptide composed of the last five alpha-helices of pfColA generated a voltage-independent conductance in planar lipid bilayer with properties very different from that of intact pfColA. Thus, helices 1 to 4 are unnecessary for channel formation, while helix 5, or some part of it, is important but not absolutely necessary. Voltage-dependence of colicin is evidently controlled by the first four alpha-helices of pfColA.

Fluorescence energy transfer distance measurements. The hydrophobic helical hairpin of colicin A in the membrane bound state.

The ion-channel-forming C-terminal fragment of colicin A binds to negatively charged lipid vesicles and provides an example of the insertion of a soluble protein into a lipid bilayer. The soluble structure is known and consists of a ten-helix bundle containing a hydrophobic helical hairpin. In this study fluorescence resonance energy transfer spectroscopy was used to determine the position of this helical hairpin in the membrane bound state. An extrinsic probe, N'-(iodoacetyl)-N'-(5-sulpho-1-naphthyl)ethylenediamine (I-AEDANS) was attached to mutant proteins each of which bears a unique cysteine residue. Five mutants I26C (helix 1), F105C (between helices 4 and 5), G166CJ (helix 8), A169C (helix 8-9), G176C (helix 9) were used. All mutants show wild-type binding activity to phosphatidylglycerol vesicles as judged by fluorescence polarization anisotropy, emission wavelength changes and brominated lipid quenching. The three tryptophan residues were used as a compound donor to AEDANS in resonance energy transfer distance determinations. The distances obtained for the soluble form were equal to those found in the crystal structure. On adding vesicles under conditions where intermolecular transfer was avoided the indicated distances increased; I26(10.9 A) F105(3.4 A), G166(3.3 A), A169(1.9 A) and G176(2.9 A). This confirms that, in the absence of a membrane potential, helices 1 and 2 open out onto the membrane surface whilst the helical hairpin remains closely packed against the rest of the structure. The insertion of this hairpin is thus not the driving force behind colicin membrane binding.

[How has the management of mentally disabled people changed?]. / Comment l'accueil des handicapés mentaux a-t-il évolué?

Greeting the mentally disabled has largely changed with time. The first attempts to assume "idiots", as Esquirol characterized them, are due to him and his followers, among whom must be mentioned Seguin and Bourneville, whose ward in Bicêtre Hospital was unfortunately suppressed in 1920. A gap appeared then, which private actions tried to fill by founding institutions for mentally disabled children. Nothing has been planned to greet them when grown adults, probably because their life expectancy was then precarious. It is not so at the present time, and their ageing creates a great problem.