Inhibition and Stimulation of Growth of Pythium by Streptomycin

Streptomycin inhibits the growth of some Oomycetes; for a review of the several possible modes of action of streptomycin in this group of fungi see Gottlieb and Shaw (3). As with many growth factors (hormones, antibiotics), the exact mechanism by which streptomycin influences the organism is only partially understood (4). In this context of uncertainty, the study of the growth of an isolate of Pythium aphanidermvaturm (Eds.) Fitzp. that is either inhibited, stimulated or not affected by streptomycin depending on environmental factors, will enlarge the picture of growth-regulating substances in fungi. Pythium irregulare Buis. and two different isolates of P. aphanidermatlum (No. 1 and 2) were used in this study. They were grown on a basal medium of Machlis solution (6) (containing 1lo glucose, 0.005M (NH4)2HPO4), with Na2SO4 H40 substituted for methionine) (1). The media consisted of either this basal medium alone, the basal medium amended with streptomycin sulfate (Nutritional Biochemicals Corp.) or these media amended with 0.015M glycine. The fungi were grown in 150 ml of these solutions in 250-ml flasks at 22 and 28 C for varying periods of time. Growth was determined by removing the mycelium from the liquid and weighing it after it had dried at 65 C for 24 h.