Measurement of acid polysaccharides in marine and freshwater samples using alcian blue
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Extracellular polymeric substances (EPS), including transparent exopolymer particles (TEP), play an important role in ocean biogeochemistry. This paper describes a simple method for measuring acid polysaccharides (APS), which are the major components of TEP and other EPS. APS were stained and precipitated with alcian blue, the precipitate was retained on a 0.2 m pore size filter and the absorbance of the filtrate was measured at 610 nm using a spectrophotometer. The color of the filtrate was inversely proportional to the amount of APS in the sample. This relationship was linear and was calibrated using gum xanthan or alginic acid as a standard. Salts interfered with the assay; therefore samples from marine environments were dialysed (1000 Da molecular weight cut-off [MWCO]) before addition of alcian blue. The assay was applied to whole water samples to a give a total concentration of APS (particulate plus dissolved) in freshwater ponds, and cultures of marine protists and seawater from the continental shelf of the northern Gulf of Mexico. The assay was effective in measuring dissolved extracellular APS after removal of particulates by filtration, although in marine samples APS molecules smaller than the MWCO of the dialysis tubing (1000 Da) were not measured. The new method has potential in studies on the biogeochemistry of particulate and dissolved APS, including TEP and its precursors. 2007, by the American Society of Limnology and Oceanography. Inc.