A comparison of the chemical characteristics of oceanic DOM and extracellular DOM produced by marine algae
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The chemical characteristics of extracellular high molecular weight (HMW) dissolved organic matter (DOM) from 3 species of marine phytoplankton were compared to HMW DOM in seawater. Thalassiosira weissflogii, Emiliania huxleyi and Phaeocystis sp., were grown in nutrient enriched seawater that had been previously ultrafiltered to remove HMW DOM. The extracellular HMW DOM produced in these cultures was isolated by ultrafiltration and characterized using nuclear magnetic resonance (NMR) spectroscopy, and molecular level analyses. All species exude DOM rich in polysaccharides, and the exudates of T. weissflogii and E. huxleyi closely resemble acyl heteropolysaccharides (APS) previously identified as major constituents of naturally occurring marine HMW DOM. Degradation of the T. weissflogii exudate alters the chemical composition of the DOM, which we attribute to differences in the reactivity of specific polysaccharides. The component within the exudate that most resembles seawater DOM has a slower degradation rate relative to the total polysaccharide fraction. Our study indicates that APS isolated from the surface ocean can have a direct algal source and that APS may accumulate in seawater as a result of its metabolic resistance.