Paola Sist

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.

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.

Sorption of CO2 in biocompatible polymers: experimental data and qualitative interpretation

Abstract Sorption of CO2 (at 308.3 and 320.1 K in the pressure range of 0–120 bar) in different biocompatible polymers (ethyl-cellulose, carboxy-methyl-cellulose, and poly-vinyl-pyrrolidone) has been measured by a gravimetric method. The experimental data are qualitative, interpreted in terms of Gibbs free energy of mixing: in particular, the role of enthalpic and entropic effects are taken into account.

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.

Organic aggregates formed by benthopleustophyte brown alga Acinetospora crinita (Acinetosporaceae, Ectocarpales)

This work presents the elemental, polysaccharide, and fatty acid compositions of benthic aggregates formed by the filamentous brown alga Acinetospora crinita, which are widely spread on the rocky bottoms of the Mediterranean Sea. The aggregates can be characterized as mineralized centers in which regeneration of nutrients and recycling of dissolved organic matter actively occur and favor the development of an abundant phytoplankton community. Analyses of the stable isotopes of C and N display their marine origin and could provide evidence of the processes that occur inside/outside of the aggregates. The monosaccharide compositions of Adriatic and Tyrrhenian mucilages produced by brown alga A. crinita were quite similar. In particular, the Adriatic sample compositions resembled the average composition of the Tyrrhenian high molecular weight exopolymers, and the observed differences could be ascribed to different degradation stages. The fatty acid patterns found for the aggregates were similar to those observed in the isolated A. crinita algae with variable contributions from embedded diatom species. The bacterial contribution to the fatty acid pool was quite low, most likely due to the known poor conditions for their heterotrophic growth.

Spontaneous patterning obtained by evaporation of Human Elastin-like Polypeptide solutions

The potential of producing patterned, bioactive coatings with Human Elastin-Like Polypeptides (HELPs) has been investigated. The physicochemical features of these compounds have evidenced some differences between the two recombinantly expressed products. By a device-free, simple route and avoiding the use of chemically unfriendly compounds, micropatterned surfaces with the ability to control cell behavior could be obtained. Thus, HELPs represent a very promising class of macromolecule for future applications in surface engineering.

Phase transition and particle formation of a Human Elastin-Like polypeptide

Elastin-Like Polypeptides are an interesting class of recombinant proteins that mimic elastin. Here we present some data about phase transition properties and particle formation features of the recombinantly expressed Human Elastin-Like polypeptide (HELP). This macromolecule shows a promising potential as vehicle for delivery and controlled release of active compounds.