Nutritional and related biological studies on the free-living soil amoeba Hartamannelta rhysodes

at 25-30 ' in a buffered physiological salt solution containing 1 % (w/v) proteose peptone and a suitable additional carbon source. Optimal growth and maximum cyst formation were obtained aerobically under constant agitation in vessels coated with silicone. The addition of a thickening agent did not improve growth. No cysts were formed at low oxygen tensions. This may reflect a fundamental metabolic block in cyst formation. Growth curves were obtained with a variety of carbon sources: glucose, maltose and mannose supported optimal growth; lactose supported unusual growth which resembled diauxie. By testing for reducing sugars, no utiliza-tion of glucose was detected. A specific chemical test for glucose revealed that glucose was utilized during growth and by resting suspensions. Through the use of uniformly labelled 14C glucose, it was possible to demonstrate that glucose was assimilated and also used as an energy source during growth. The osmotic concentra-tion required for optimal growth was in itself not optimal when the total osmotic pressure was kept constant and the concentration of utilizable carbon sources was decreased