Zoogloea ramigera, a gram-negative bacterium found in activated sludge, formed volutin granules when excess orthophosphate was added to a phosphate-starved culture. These volutin granules were stainable by hydrogen sulfide after lead acetate treatment and extractable by N-perchloric acid but were not adsorbed by activated charcoal. They appeared to consist of inorganic polyphosphate. Optimum granule formation in the arginine broth required 10 g of glucose, 3 mg of phosphate, and 1 to 20 mg of magnesium per liter of medium. At an Mg2+ concentration of 1 mg/liter, very large granules appeared which often appeared to fill the cell. An excess of glucose, orthophosphate, or magnesium reduced granule formation. In the absence of sulfate, moderate granulation occurred in arginine broth before the addition of excess orthophosphate; granulation did not increase after the addition of phosphate.
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