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

During the stationary phase of a batch culture of the epipelic diatom Cylindrotheca closterium, accumulation of exopolysaccharides and intracellular carbohydrates was observed. When nitrogen was added to the culture in the stationary phase, growth was resumed and the accumulation of exopolysaccharides was delayed. This indicated that nitrogen depletion caused cessation of growth, and stimulated exopolysaccharide accumulation. Exopolysaccharide accumulation was also stimulated when cells were either resuspended in medium lacking N or P, or when they were inoculated in medium with low concentrations of N or P. Growth was not immediately affected by low N or P concentrations. S depletion only resulted in exopolysaccharide accumulation when growth was affected. Si or Fe depletion did not stimulate exopolysaccharide accumulation, even when growth rates were lowered. Apparently, stimulation of exopolysaccharide accumulation is dependent on the type of nutrient depletion. Intracellular storage carbohydrates did not accumulate when cells were incubated at low N or P concentrations. Cells grown with ammonium as nitrogen source produced more carbohydrates (both extracellular and intracellular) than cells grown with nitrate as nitrogen source, indicating that both exopolysaccharides and intracellular carbohydrates accumulated as a result of overflow metabolism.