Exopolysaccharide production by the epipelic diatom Cylindrotheca closterium: effects of nutrient conditions

During the stationary phase of a batch culture of the epipelic diatom Cylin drotheca closterium, accumulation of exopolysaccharides and intracellular c arbohydrates was observed. When nitrogen was added to the culture in the st ationary phase, growth was resumed and the accumulation of exopolysaccharid es was delayed. This indicated that nitrogen depletion caused cessation of growth, and stimulated exopolysaccharide accumulation. Exopolysaccharide ac cumulation was also stimulated when cells were either resuspended in medium lacking N or P, or when they were inoculated in medium with low concentrat ions of N or P. Growth was not immediately affected by low N or P concentra tions. S depletion only resulted in exopolysaccharide accumulation when gro wth was affected. Si or Fe depletion did not stimulate exopolysaccharide ac cumulation, even when growth rates were lowered. Apparently, stimulation of exopolysaccharide accumulation is dependent on the type of nutrient deplet ion. Intracellular storage carbohydrates did not accumulate when cells were incubated at low N or P concentrations. Cells grown with ammonium as nitro gen source produced more carbohydrates (both extracellular and intracellula r) than cells grown with nitrate as nitrogen source, indicating that both e xopolysaccharides and intracellular carbohydrates accumulated as a result o f overflow metabolism. (C) 2000 Elsevier Science B.V. All rights reserved.