Rouf, M. A. (Washington State University, Pullman) and J. L. Stokes. Isolation and identification of the sudanophilic granules of Sphaerotilus natans. J. Bacteriol. 83:343-347. 1962.-The characteristic and prominent sudanophilic granules in five strains of Sphaerotilus natans were shown to be composed of poly-beta-hydroxybutyric acid by the method of isolation, melting point determinations, and infrared absorption spectrum analyses. The polymer may account for 11.0 to 22.5% of the dry weight of the cells. It accumulates during active growth of S. natans and decreases sharply in amount after maximal growth. It accumulates to an equal extent in cultures with and without sheaths.