Polysaccharide Chain Features and Amorphous Matrix Morphology of Mucilage Aggregates of the Northern Adriatic Sea

Ranieri Urbani and Paola Sist

Dept. of Biochemistry, Biophysics and Macromolecular Chemistry - Univ. of Trieste

A systematic study has been undertaken to evaluate the role of the saccharidic components in the marine aggregates formation in terms of the primary structure and macromolecular properties. The mucilaginous materials appeared in the Northern Adriatic Sea during June and July 2000, 2001 and 2002 have been collected. A quantitative method for exhaustive extraction, purification and isolation of the polysaccharide fractions have been studied. Detailed chemical analysis of monosaccharides, uronic and sulphate functional groups of polysaccharides has been carried out showing that galactose is the major monosaccharide component (35-50% w/w) of fractions FA and FB which are to be considered mainly formed by extracellular polysaccharides. Mannose, xilose, rhamnose and fucose are minor components throghout the samples (5-12%). Gel permeation analysis performed in the range 104-106 of molecular weights (MW) reveals that in the fractions FA and FB two molecular weight distributions are present, one at higher (about 220,000 Da) and the second at lower MW (about 10,000 Da). Light scattering and viscometric measurements of macromolecular properties of saccharidic chains (average molecular weight, radius of gyration, second virial coefficient, viscosity) and their dependence on chemical and physical conditions commonly found in the marine environment show that polysaccharidic chains are very stiff and elongated and their conformation can be thought as a fairly rigid chain. The presence of charged groups, both uronic and sulphate, determines that polyelectrolytic behaviour which plays an important role in the aggregation processes. Morphological study of mucilage amorphous matrices have been carried out by mean of Scanning Electron Microscopy (SEM) technique showing that mucilage matrix is a tri-dimensional network of fibrillar structures formed mainly by supra-molecular structuring of polysaccharidic chains.

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