The Atlantis Poem in the Timaeus-Critias

Plato, in the Timaeus, links the story about Atlantis with a noble tradition that Solon discovered near the Nile Delta. In the Critias, Plato refers to the idea that Solon was planning to write a poem about Atlantis and also suggests that the poem was to be based on a written record. But l’existence of a poem about Atlantis is not plausible. Plato brings out, so, the relationship between the Atlantis story and the facts of the past, between his family and the enquiry of Socrates and between the story about Atlantis and the literary production

CbpA: a novel surface exposed adhesin of clostridium difficile targeting human collagen

Clostridium difficile is the leading cause of antibiotic-associated diarrhea and pseudomembranous colitis. While toxins A and B are primarily responsible for the pathogenesis, determinants of bacterial adherence are also essential for intestinal colonization process. We focused our study on a novel member of the MSCRAMM family, named CbpA (Collagen binding protein A) for its adhesive properties towards these components of the extracellular matrix (ECM). We demonstrate that CbpA, which carries an LPXTG-like cell wall anchoring domain, is expressed on the bacterial surface of C. difficile and that the recombinant form binds at high affinity to collagen I and V (apparent KD in the order of 10-8 and 10-9 M respectively). Such evidences were confirmed by confocal microscopy studies showing the association of the protein with Type I and V collagen fibers produced in human fibroblasts and mouse intestinal tissues. However, the collagen binding activity of the wild-type C. difficile 630 strain was indistinguishable to cbpA knock-out strain. To overcome this apparent clostridial adherence redundancy, we engineered a Lactococcus lactis strain for the heterologous expression of CbpA. By this approach, we were able to demonstrate that when exposed on the surface of L. Lactis, CbpA significantly enhances the ability of the bacterium to interact with collagen and to adhere to ECM-producing cells. To prove the specificity of the interaction, we showed that the binding activity of L. lactis-CbpA strain was prevented by pre-incubating bacteria with an antiserum raised against CpbA. The results reported in this study suggest a role for CpbA in the adherence to intestinal submucosa during C. difficile colonization of the gut

CbpA: a novel surface exposed adhesin of clostridium difficile targeting human collagen

Clostridium difficile is the leading cause of antibiotic-associated diarrhea and pseudomembranous colitis. While toxins A and B are primarily responsible for the pathogenesis, determinants of bacterial adherence are also essential for intestinal colonization process. We focused our study on a novel member of the MSCRAMM family, named CbpA (Collagen binding protein A) for its adhesive properties towards these components of the extracellular matrix (ECM). We demonstrate that CbpA, which carries an LPXTG-like cell wall anchoring domain, is expressed on the bacterial surface of C. difficile and that the recombinant form binds at high affinity to collagen I and V (apparent KD in the order of 10-8 and 10-9 M respectively). Such evidences were confirmed by confocal microscopy studies showing the association of the protein with Type I and V collagen fibers produced in human fibroblasts and mouse intestinal tissues. However, the collagen binding activity of the wild-type C. difficile 630 strain was indistinguishable to cbpA knock-out strain. To overcome this apparent clostridial adherence redundancy, we engineered a Lactococcus lactis strain for the heterologous expression of CbpA. By this approach, we were able to demonstrate that when exposed on the surface of L. Lactis, CbpA significantly enhances the ability of the bacterium to interact with collagen and to adhere to ECM-producing cells. To prove the specificity of the interaction, we showed that the binding activity of L. lactis-CbpA strain was prevented by pre-incubating bacteria with an antiserum raised against CpbA. The results reported in this study suggest a role for CpbA in the adherence to intestinal submucosa during C. difficile colonization of the gut

Calixarene-based langmuir monolayers : from crystallization templates to metal organic networks

Molecular self-assembly plays a pivotal role in biological processes and living organisms can be considered as the result of the self-assembly of discrete molecular building blocks into sophisticated functional structures. Biology provides countless examples of complex and functional hierarchical self-assembled structures ranging from protein and nucleic acid biosynthesis to biological membranes self-assembly. Although Nature may produce such structures with an extreme efficieny, man-made chemical strategies to produce large covalent architectures are typically more complex and tedious. Due to the difficulty to precisely control the formation of large macromolecular architecture through covalent synthetic strategies, the self-assembly approach has been extensively exploited for the creation of supramolecular entities. Amphiphiles are compounds able to self-assemble in myriad supramolecular structures such as micelles, vesicles, nanosheets, nanorods, nanotubes and nanofibers, to name but a few. The shape of the resulting supramolecular assembly is dependent on the structure of the amphiphilic building block and type of solvent. Among all kinds of natural and synthetic amphiphiles, macrocyclic amphiphiles are of particular interest due to the possibility to conveniently control the hydrophilic/lipophilic balance of the final amphiphilic structure. The basket-like rigid conformation of calix[4]arenes, and the possibility to selectively functionalize both the upper and lower rim, make these molecules attractive building blocks for the design of amphiphilic compounds. Amphiphilic calix[4]arenes that are essentially insoluble in water self-assemble as monomolecular films at the air-water interface, forming Langmuir monolayers, where the aliphatic chains point into air while the polar functions are immerged into the subphase. Langmuir monolayers of amphiphilic calix[4]arene derivatives have been demonstrated to interact with a wide range of solutes, ranging from ions to macromolecules. In addition to this, calix[4]arene-based monolayers have been shown to induce the interfacial crystallization of inorganic and organic solids. The polar heads of the macrocycles act as recognition units for the interfacial nucleation of the to-be-crystallized molecules. Electrostatic interactions, along with geometrical complementarity between the macrocycles polar functions and the solute are the determining factors for the interfacial crystal growth. In this thesis, the ability of Langmuir monolayers of a p-carboxycalix[4]arene derivative to act as templates for the crystallization of gabapentin (GBP), an active pharmaceutical ingredient used to relieve neuropathic pain, with a control over its polymorphism is reported. The suitable chemical modification of the upper and lower rim of calix[4]arenes allows producing stable amphiphilic macrocycles able to form stable Langmuir monolayers at the air-water interface with strong affinities towards ions. The affinity of calix[4]arene-based Langmuir monolayers towards ions is mainly owing to the presence of a cavity that allows for the encapsulation of the ions, coupled with multiple polar ligating functions at the p-positions that strongly interact with the solute. In this thesis, the recognition properties of Langmuir monolayers of a series of p-carboxy- and p-aminocalix[4]arene derivatives towards strong, i.e. CuCl2, CoCl2, NiCl2 and MnCl2, and weak, i.e. HgCl2, electrolytes are reported. The effect of the inorganic compounds on the self-assembly properties of the calix[4]arene-based Langmuir monolayers is investigated by means of surface pressure-area compression isotherms, Brewster angle microscopy (BAM) and synchrotron-based X-ray diffraction techniques. Notably, it has been demonstrated that the structure of the macrocycle has a crucial effect on its interfacial organization. Upon interaction of a long chain, i.e. C12, p-carboxycalix[4]arene derivative with Cu2+ ions at the air-water interface, the corresponding calix[4]arene-based monolayer is mainly amorphous. On the other hand, Langmuir monolayers of the short chain (C3), structural analogue on aqueous Cu2+ ions subphases possess significantly large and highly ordered structures. It is assumed that the interfacial self-assembly of the long chain p-carboxycalix[4]arene derivative is mainly driven by van der Waals interactions among the aliphatic chains, which contribute to the partial disordered monolayer structure. On the contrary, the self-assembly of the short chain p-carboxycalix[4]arene derivative is driven by π-π interactions among aromatic rings of neighboring amphiphiles, which contribute to the highly ordered structure of the monomolecular film

Morphometric differences between two sympatric species of anolis (Reptilia: Squamata: Polychrotidae)

There has been a recent surge of interest in the study of evolutionary relationships between morphology and microhabitat use in lizards in general. Lizards of the genus Anolis, most notably the Caribbean species, have become a model system in this respect. Although the mechanisms of Anolis locomotion have received considerable attention, however, little is known regarding locomotor performance of species of mainland Anolis in nature, and their morphological diversity. The goal of this study was to investigate the differences in morphology between Anolis humlis and Anolis limifrons, sympatric species that exploit different structural microhabitats (arboreal vs. ground-dwelling) with different locomotion challenges. A principal components analysis was performed on morphometric data for the two species that illustrates differences between the species. A multivariate analysis of variance on selected variables suggested only three variables: manus length, tail length and forelimbs length showed significant differences with respect to microhabitat use. Lizards that occupy vertical habitats (arboreal) tend to have longer tails and longer hind limbs (included the longer fourth toe) whereas lizards in terrestrial habitats have wider and flatter bodies and head and longer forelimbs. These morphological characteristics may allow climbing lizards to keep their centre of mass close to the substrate, while in terrestrial lizards they would enhance maneuverability and support weight during level running.Fil: Tulli, María José. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación Miguel Lillo. Dirección de Zoología. Instituto de Herpetología; Argentin

S-duality and the universal isometries of instanton corrected q-map spaces

Given a conical affine special K\"{a}hler (CASK) manifold together with a compatible mutually local variation of BPS structures, one can construct a quaternionic-K\"{a}hler (QK) manifold. We call the resulting QK manifold an instanton corrected c-map space. Our main aim is to study the isometries of a subclass of instanton corrected c-map spaces associated to projective special real (PSR) manifolds with a compatible mutually local variation of BPS structures. We call the latter subclass instanton corrected q-map spaces. In the setting of Calabi-Yau compactifications of type IIB string theory, instanton corrected q-map spaces are related to the hypermultiplet moduli space metric with perturbative corrections, together with worldsheet, D(-1) and D1 instanton corrections. In the physics literature, it has been shown that the hypermultiplet metric with such corrections must have an $\mathrm{SL}(2,\mathbb{Z})$ acting by isometries, related to S-duality. We give a mathematical treatment of this result, specifying under which conditions instanton corrected q-map spaces carry an action by isometries by $\mathrm{SL}(2,\mathbb{Z})$ or some of its subgroups. We further study the universal isometries of instanton corrected q-map spaces, and compare them to the universal isometries of tree-level q-map spaces. Finally, we give an explicit example of a non-trivial instanton corrected q-map space with full $\mathrm{SL}(2,\mathbb{Z})$ acting by isometries and admitting a quotient of finite volume by a discrete group of isometries.Comment: 56 page

Proposta di un protocollo pratico per la valutazione dell'indice di condizione nei mitili (M. galloprovincialis)

The indices for the yields evaluation, as well as condition index (CI), that relate the amount of the meat with shell weight are widely used both for scientific research both for shellfish farming management, representing the main tools for the evaluation of merchantable traits in bivalve mollusks. CI values changes are due to a variety of factors, including mainly food availability and physiological status but also animal health and water temperature and salinity. Different methods are used to calculate IC value. in the mussels. The present study is intended to present a simple protocol for the CI mussels (M. galloprovincialis) evaluation able to mediate scientific rigor needs with the management needs in order to adopt an uniform procedure