Ranieri Urbani

Abundance and chemical characterization of extracellular carbohydrates released by the marine diatom Cylindrotheca fusiformis under N- and P-limitation

The effect of P- and N-depletion on the production and molecular-level composition of extracellular carbohydrates released by the diatom Cylindrotheca fusiformis was examined in axenic batch cultures. Inorganic phosphorus depletion caused a higher release of organic carbon per cell compared to nutrient-replete and nitrogen-limited conditions. Gas-chromatographic analysis of the monosaccharide composition of the dissolved fraction showed galactose to be the major component of the exopolymers (33 – 42%). In the P-limited treatment, an increase of galactose content and a decrease of glucose was found, while the composition of the remaining saccharides was almost unaffected. The results point out the relevance of phosphorus limitation not only in causing an increase in total exopolysaccharide production, but also in affecting the neutral aldose composition of the dissolved carbohydrates released by C. fusiformis, with heteropolysaccharides being more abundant than glucan. The overall sugar composition of the exopolymers released under the most severe P-depletion was similar to that of natural mucilage samples collected in the Northern Adriatic Sea during the Summer 2000 event of massive aggregation.

Macromolecular and solution properties of Cepacian: the exopolysaccharide produced by a strain of Burkholderia cepacia isolated from a cystic fibrosis patient

Light scattering and viscosity measurements were carried out on the previously chemically characterised exopolysaccharide produced by a strain of Burkholderia cepacia isolated from a cystic fibrosis patient. The same exopolysaccharide was also produced by other clinical strains in different laboratories. Therefore, the name Cepacian is now proposed for this exopolysaccharide. Experiments performed as a function of the ionic strength on the native polymer revealed a change in the overall shape of the polymer at low ionic strength. This behaviour was absent in the de-acetylated sample. Potentiometric titrations and light scattering experiments carried out on the acidic form of the native polymer revealed the formation of macromolecular aggregates with a stoichiometry n and 2n stabilised by interactions involving the uronic acid residues.

Physicochemical properties of the exocellular polysaccharide from Cyanospira capsulata

This paper reports on the chemical structure and on some physicochemical properties of a new exopolysaccharide, CC-EPS, secreted by a filamentous nitrogen-fixing cyanobacterium, Cyanospira capsulata. Solution properties of CC-EPS were studied with the aim of characterizing the conformational state of the polysaccharide in water and in aqueous salt solution, in view of the peculiar rheological properties. Because the molecule has two different uronic acid residues, a variation of pH and/or ionic strength was considered to be the best perturbation to disclose any possible ordered structures. We found no evidence for a cooperative conformational transition from the change of the chiro-optical properties or from the smooth increase of pKa as a function of the degree of ionization, alpha, of the polyacid. The same conclusion was drawn from the study of the temperature dependence and ionic strength dependence (in the range up to 0.1 M NaCl) of solution properties. The data suggest that the solution conformation of CC-EPS is a random coil with a chain flexibility comparable to that of alginate.

Enthalpy relaxation and glass transition behaviour of sucrose by static and dynamic DSC

Abstract The relaxation process of the sucrose in the glassy state and its glass transition are studied by differential scanning calorimetry in both the conventional and the dynamic mode. The data on the kinetics of glassy relaxation are experimentally evaluated by measuring the enthalpy relaxation peaks as a function of the ageing times at three different ageing temperatures, namely 45, 55 and 60°C. It is shown that the ageing process is a complex phenomenon with a rather large distribution of relaxation times. The value of the breath of the distribution of relaxation processes, β, is 0.32 and it is in the lower range of the distributions commonly observed. The dynamic components of the heat capacity ( C ′ p and C ″ p ) have been obtained from the experiments carried out at different frequency of temperature modulation ( ν =8.3−83 mHz). These components are unaffected by the ageing process and therefore are more reliable for the correct T g determination. The activation energies for the relaxation process and for the glass transition process are also evaluated.

Conformational features of carrabiose polymers: I. Configurational statistics of κ-carrageenan

Potential energy functions evaluating both repulsive-attractive van der Waals non-bonding interactions and electrostatic interactions have been used to evaluate the conformational energies of the repeating units of the κ-carrageenan polymers. Structural parameters have been obtained by minimization MNDO procedures (MOPAC). Energy maps have been calculated for the (1–3)α- d -galactose-4-sulphate (GS) and the (1–4)-3,6-anhydro-α- d -galactose (A) residues, taking into account the conformational freedom of the sulphate group. The configurational statistics of the random coiled κ-carageenan chain have been explored, disclosing a highly flexible character, which can mainly be ascribed to the random occurrence of two different conformers of the GS-A dimeric unit.

Polyelectrolytic effects in semi-flexible carboxylate polysaccharides. Part 2

A statistical model is presented in which an ionic polymer is taken as a linear arrangement of flexible segments (similar to the spring-bead model). This model is used to represent semi-flexible linear ionic polysaccharides in solution. The distribution of end-to-end distances is taken from Monte Carlo calculations of the amylosic chain conformation and combined with Mannings counterion condensation theory of linear polyelectrolytes. The excess thermodynamic properties are then calculated as a function of the degree of ionization and of a number of physical variables. The results show that the statistical average of thermodynamic functions taken over the conformational states is not equivalent to the thermodynamic function of the average conformation. This has important implications for the correct comparison of theoretical prediction with the experimental results.

Polymer networks produced by marine diatoms in the northern Adriatic sea.

Using high resolution molecular technique of atomic force microscopy, we address the extracellular polymer production of Adriatic diatom Cylindrotheca closterium analyzed at the single cell level and the supramolecular organization of gel phase isolated from the Northern Adriatic macroaggregates. Our results revealed that extracellular polysaccharides freshly produced by marine diatoms can self-assemble directly to form gel network characteristics of the macroscopic gel phase in the natural aquatorium. Based on the experiments performed with isolated polysaccharide fractions of C. closterium and of macroaggregates gel phase, we demonstrated that the polysaccharide self-assembly into gel network can proceed independent of any bacterial mediation or interaction with inorganic particles.

Comparison of thermal behavior of two recombinantly expressed human elastin-like polypeptides for cell culture applications.

Two synthetic genes that code for artificial proteins have been constructed that were modeled on the most regularly repeated hydrophobic domain of human tropoelastin. We compare the physicochemical properties of the recombinant products that differ in their primary structure; the alanine/lysine-rich cross-linking domains, which are highly conserved in mammalian tropoelastin, were either present or absent in the recombinant products. Both biopolymers showed thermoresponsive properties, and variations were observed that were dependent on solution conditions. Cell compatibility was assayed using the biopolymers as coating agents in culture experiments with a neuroblastoma cell line; cell adhesion and proliferation effects were evaluated. The cells were found to retain their neural differentiation potential. The data presented in our work support the usefulness of these versatile biopolymers for a variety of applications related to biotechnology and biomedicine.

Conformational features of galacturonans. II. Configurational statistics of pectic polymers.

The unperturbed dimensions of poly-alpha-D-galacturonic acid (PGA) as a function of the degree of polymerization (n) and degree of ionization (%GalA-) have been determined by molecular mechanics and Monte Carlo methods. Chain extensions appear to depend substantially on contributions arising from local redistributions of charge on charged and uncharged galacturonic acid residues. Inclusion of methyl-esterified galacturonic acid units results in increased chain extensions. Incorporation of alpha-(1-->2)-L-rhamnose units causes abrupt changes in chain propagation and a reduction in calculated chain extension.

Diatom Polysaccharides: Extracellular Production, Isolation and Molecular Characterization

This chapter aims to give an overview on the isolation procedures and techniques for macromolecular characterization of extracellular polysaccharides from laboratory cultures of selected diatom species and from native marine aggregates. The emphasis is given to the macromolecular behavior of isolated polysaccharide in solution and their propensity to aggregate and to form highly structured systems like gels. This was made possible by developing protocols and procedures for isolation/separation and application of physico-chemical techniques like laser light scattering and viscosimetry to marine and culture samples. A separate section is devoted to atomic force microscopy, the most versatile nanotechnology platform widely used in polymer biophysics and diatom nanotechnology. The first force spectra experiments conducted on isolated polysaccharide fibrils and on marine gel polysaccharide network are presented together with recently published works on high resolution imaging. Diatom exopolysaccharide force spectroscopy and interactions with nanoparticles are identified as future prospective contributing to the growing field of nanoecology and for rational design of polysaccharide gels with desired properties.