The role of reduced sulfur species in the coalescence of polysaccharides in the Adriatic Sea

Massive mucilage events occur in the Northern Adriatic Sea presumably by cy toplasmic excretions from deteriorated diatoms. During three such events in the summer of 1991, 1997 and 1998 the presence of reduced sulfur species ( RSS) was determined in samples of macroaggregate using electrochemical meth ods (in-phase alternating current (AC) and linear sweep voltammetry). The d etected levels of sulfur, expressed as equivalent to sulfide concentrations , were about 200 nM. In the same mucilage samples, concentrations of organi c matter were determined in the range from 60 to 600 mg/l of total organic carbon (TOC). The physico-chemical properties of organic matter in the macr oaggregates correspond to those of polysaccharides of very high molecular m ass. Scanning confocal laser microscopy (SCLM) and fluorescent molecular pr obes for sugars (the lectins concanvaline A (Con-A)) showed the transformat ion of polysaccharide polymer structure resulting in the formation of very stable filaments and layers after the treatment of mucilage samples with so dium sulfide. Commercial polysaccharides of bacterial and algal origin (xan than, carrageenans types I and II, dextran-T-500) have been used to simulat e macroaggregate formation under laboratory conditions after treatment with sodium sulfide. Raman spectroscopy indicated that for all model polysaccha rides used, sulfide interaction occurred, as evidenced by visible change of the O-H stretching region in the vibration spectra of the water molecules. Our data suggest that the aggregated polysaccharides from the Adriatic Sea are: (1) structurally affected by addition of sulfide as was the case for m ost of the model polysaccharides, and (2) the stabilizing effect of sulfide on the aggregated polysaccharides is due to the formation of sulfur-organi c compounds. (C) 2000 Elsevier Science B.V. All rights reserved.