Cell lysis and release of particulate polysaccharides in extensive marine mucilage assessed by lipid biomarkers and molecular probes

Abstract

During the massive mucilage event in the northern Adriatic Sea in July 1991 samples of macroaggregate were fixed in different ways: with formaldehyde, deep frozen and freeze-dried. Conventional microscopy (light and epifluorescence) revealed different autotrophic species embedded in gelatinous matrix. Cyanobacteria and heterotrophic bacteria were also identified. Scanning confocal laser microscopy (SCLM) and fluorescent molecular probes (the lectins concanavalin A and UEA-I) showed wall-free cytoplasm and particulate polysaccharides leaking from the envelopes of broken cells in the matrix. The extensive cell lysis was supported by the observation of cyloplasm-free cytoskeletons, stained by the molecular probe phalloidin. High concentrations of triglycerides (30% of total lipids) and free fatty acids (22%) along with very low concentrations of phospholipids (2%) also indicated massive cell degradation in freeze-dried material. The mucilage observations were compared with those of a natural plankton community grown under high nutrient conditions using the same techniques. Free polysaccharides were observed as globular flocs (marine snow) during in situ enrichment experiments and intracellular polysaccharides as carbon storage materials in autotrophic organisms. No strings, filaments, layers, cell lysis or lipid classes indicating strong cell biodeterioration were observed in a 1 mo controlled experiment during an algal bloom.