ABSTRACT: Extracellular polymers of Phaeocystis globosa and P. antarctica were characterized by elemental analysis, X-ray photoelectron spectroscopy (XPS), and matrix-assisted laser desorption ionization-time of flight-massspectrometry (MALDI-TOF-MS) analysis. The 2 species were grown in axenic and bacterized cultures to examine the effect of bacterial degradation on the composition of the extracellular polymers. The C:N ratios for extracellular polymers from P. globosaand P. antarctica grown under these conditions were lower (9) than in previous reports (>12). P. antarctica polymer C:N was significantly lower than that of P. globosa. Contrary to expectations, the polymer C:N frombacterized cultures was slightly lower than from axenic cultures. XPS analysis indicated that the polymers are carbohydrate-rich, and MALDI-TOF-MS analysis showed that the nitrogen was not proteinaceous, but probably originated from low molecular weightcompounds such as amino sugars. The low C:N ratios suggest that extracellular polymers may directly provide a substrate for bacteria and heterotrophic protists without the need for other sources of nitrogen.