The Influence of Vitamin BIZ on Growth Rate and Cell Composition of the Flagellate Ochromonas malhamensis

SUMMARY: In cultures of the flagellate Ochromonas malharnensis the rate of growth is determined by the concentration of cyanocobalamin up to a limit a t which a maximum growth rate is achieved. In organisms grown exponentially with different rate-limiting concentrations of cyanocobalamin, the amounts of protein and nucleic acids were approximately proportional to the rates at which the organisms had grown. With increasing growth rate the concentrations of riboflavin, nicotinic acid, pantothenic acid and chlorophylls increased. Carbohydrate showed little change, whereas fat and ‘free ’ amino-nitrogen diminished in concentration as the growth rate increased. In cultures of 0. malhamensis grown with limiting or near-limiting concentrations of cyanocobalamin and with increasing concentrations of chloram-phenicol, the rates of division declined asymptotically to a low value corresponding with 500 pg. chloramphenicol/ml. culture medium. Inhibition of growth caused by the antibiotic was annulled by increasing the concentration of cyanocobalamin in the culture medium. A variety of cultural and nutritional factors can influence the balance of com