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An Autoinhibitory Substance Produced by Platydorina caudata Kofoid ¹

^a Department of Botany, University of Kentucky, Lexington, Kentucky 40506

An inhibitory substance was obtained from culture filtrates of Platydorina caudata Kofoid, (a colonial, green flagellate), in which death of the culture had occurred. The cessation of growth occurs before, and is seemingly independent of, medium depletion. The substance can be detected as early as the 15th day, and by the 25th day growth is completely suppressed. A bioassay method for quantitating the activity of the substance was devised. The substance is heat-labile, nondialyzable, acid-labile, and apparently specific for Platydorina. The substance resists short periods of freezing and bacterial contamination. Preliminary results suggest that trypsin destroys activity of the substance.

¹ This investigation is a portion of a dissertation submitted to the graduate school of Indiana University in partial fulfillment of the requirements for the degree of Doctor of Philosophy.