A dye binding assay for the quantification of soluble and cell-bound acidic polysaccharides produced by red algae

Polysaccharides produced in technical scale from red algae serve in a variety of industrial applications. Ruthenium red (RR) is a cytochemical stain which has been used to visualize these mostly acidic polysaccharides in light microscopy. The binding of RR to algal polysaccharides is highly dependent on the ionic strength of the surrounding medium. The dye is firmly bound at low ionic strength, but is released at increasing salt concentrations. These properties were exploited to develop a new method to quantify the amount of cell wall material synthesized by algal cells under different physiological conditions. Soluble or extracted polysaccharides are quantified by a dot-blot procedure with subsequent image analysis, while cell-bound polysaccharides are determined in situ by a dye-binding assay followed by photometry. In comparison to the current methods of quantification, the new assay is quick, reliable, and avoids extensive use of hazardous chemicals.