Physical characterization and diel dynamics of different fractions of extracellular polysaccharides in an axenic culture of a benthic diatom

Abstract

The excretion of extracellular polymeric substances (EPS) by an axenic culture of the benthic diatom Cylindrotheca closterium was investigated. Two sequential extraction steps proved to be sufficient to remove the bulk of the EPS present. Soluble EPS was recovered by a simple centrifugation step and represented a fraction that was not or was only loosely associated with diatom cells. For the extraction of bound EPS, different procedures were compared. The best results were obtained using distilled water as extraction solvent (1 h, 30 mC). The sugars that were recovered using this procedure were typically associated with aggregates of diatoms. In addition to the distinct differences in localization of the different types of EPS, their temporal dynamics differed in relation to the light-dark cycle. Soluble EPS were continuously released into the medium at a rate of 1n6 pg cell −" day −" . In contrast, the production of bound EPS was highly light-dependent. In the dark, this bound EPS rapidly disappeared, probably as the result of its utilization by the diatoms.

The carbohydrates of Phaeocystis and their degradation in the microbial food web

“…The change in colony shape and appearance at the end of Phaeocystis blooms (e.g., Verity et al 1988;Rousseau et al 1994) is therefore not reflected in the aldose composition of the mucopolysaccharides. This is different from the situation reported in diatoms, where upon nutrient limitation, the benthic diatom Cylindrotheca closterium excretes a separate extracellular polysaccharide with a different monosaccharide composition compared to optimal growth conditions (De Brouwer et al 2002;Underwood et al 2004). Phaeocystis acts as a secretory cell; mucopolysaccharides are excreted in a way similar to animal cells and vascular plants in which the regulated export of cellular products takes place via exocytosis.…”

Use of Fluorophore-Conjugated Lectins To Study Cell-Cell Interactions in Model Marine Biofilms

“…Two factors that are more general but very important are the ways in which field samples are processed and the subsequent EPS extraction method that is used. It is now recognized that lyophilization of diatom cells compromises their cell membranes (15,17,33,41); thus, extracts made from such cells may contain intracellular, as well as extracellular, components of the cells. A comprehensive inventory of diatom polymers was prepared for Pinnularia viridis by Chiovitti et al (8).…”

“…In the first place, it is very difficult to compare work on extracellular polymers (extracellular polymeric substances [EPS]) extracted from field samples (3,15,26,30,36,38,43,46) with work on EPS extracted from axenic cultures in the laboratory (14,17,33,34,43,44). Nutritional status is important in regulating EPS (34), and the nutritional status of field samples is usually unknown at the spatial resolution influencing the cell.…”

“…Thus, the time of day at which field samples are taken is also important. It is recognized that diatoms synthesize more than one type of EPS (3,16,33,37,41,44) and that the different types can have different roles (16,17,32). Many workers regard the EPS as being wholly carbohydrate.…”

“…Nutritional status is important in regulating EPS (34), and the nutritional status of field samples is usually unknown at the spatial resolution influencing the cell. Similarly, the light regimen under which the diatom cells are grown influences radically both the synthesis and the accumulation of EPS (17,30). Thus, the time of day at which field samples are taken is also important.…”