Observations on the growth of Dictyostelium discoideum in axenic medium: evidence for an extracellular growth inhibitor synthesized by stationary phase cells.

By analysing the growth kinetics of Dictyostelium discoideum amoebae in varying combinations of the components of the nutrient medium HL-5 (Cocucci & Sussman, 1970), we have demonstrated that Dictyostelium amoebae enter stationary phase when they deplete the medium of one or more nutrient components. However, if the medium of a stationary phase culture is supplemented with any of the initial components of HL-5 medium and even when supplemented with all components of HL-5 medium, it does not support the growth of freshly inoculated cells, indicating that stationary phase cultures produce a potent growth inhibitor. The possible function of this inhibitor is discussed.