A polyphosphate-accumulating Microlunatus phosphovorus bacterium, strain NM-1, with the abilities of accumulating polyphosphate under aerobic conditions and releasing phosphate under anaerobic conditions, was successfully immobilized in polyacrylamide gel. Strain NM-1 still exhibited the phosphate uptake and release activities after immobilization as observed in activated sludge with enhanced phosphate removal activity. Under anaerobic conditions, the immobilized cells could take up substrates by deriving energy from the hydrolysis of polyphosphate to orthophosphate. The ratio of the amount of phosphorus released to that of TOC (total organic carbon) taken up was approximately 1 g-P/g-TOC in a synthetic medium. The initial phosphate release rate varied between 10 and 30 mg-P/g-cell . h depending on the initial TOC concentration. The TOC concentration required to induce sufficient phosphate release was about 1,000 mg/l for a 12,500 mg/l immobilized cell concentration. Under aerobic conditions, the immobilized cells rapidly took up the phosphate previously released. The phosphate uptake rate was about 10-20 mg-P/g-cell . h. The optimum pH and temperature for phosphate release and uptake were 8 and 25 degrees C, respectively.