Rates and elemental ratios of nutrient released by a bacterivorous flagellate (Spumella sp.) were examined during the exponential and stationary growth phases of the flagellate. Two types of an isolated bacterium were used as prey : one was phosphorus-rich (C: N : P molar ratio=59 : 13: 1) and the other was phosphoruspoor (C: N : P=79: 17: 1). Specific release rates by the flagellate of ammonium, dissolved inorganic and organic phosphorus (DIP and DOP) were much higher during the exponential

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... wth phase than during the stationary one. Ammonium and DIP release rates in the experiment using the P-rich bacterium (Experiment 1) were not so remarkably different from those using the P-poor bacterium (Experiment 2) during both phases. However, DOP release rates were much higher in Experiment 1 than in Experiment 2 during both phases. Ratios of ammonium released to total dissolved phosphorus released were significantly lower in Experiment 1 than those in Experiment 2 during both phases. Further, these ratios were higher than bacterial N : P ratios in both experiments. N : P ratios of nutrients released by the flagellate could have been determined by bacterial N : P ratios, but the release appeared more efficient for nitrogen than for phosphorus.