Relation of Hydrogen-Ion Concentration to Growth of Chlorella and to the Availability of Iron

Abstract

1. The rate of growth of Chlorella in highly buffered nutrient solutions is directly influenced by the H-ion concentration when the PH is less than 5.7. The acid limit for growth of this organism in the culture media tested is 3.4. 2. In solutions in which the PH is higher than 5.7, the availability of iron becomes a limiting factor for growth. 3. Certain organic compounds, especially sodium citrate, are effective in holding iron in solution in alkaline buffer mixtures of 7.4. When calcium is present, however, the iron is completely removed from such solutions by the precipitated calcium phosphate, probably as the result of adsorption. 4. Since calcium is not essential for the growth of Chlorella it can be omitted entirely from the culture solution. Iron can then be maintained in alkaline solutions in a form available for growth by the addition of sodium citrate. In such solutions maximum growth occurred at 7.5. The alkaline limit for growth has not as yet been established. 5. In unbuffered nutrient solutions, marked changes in the H-ion concentration may be brought about by the unequal absorption of ions, resulting in increased acidity, which in turn renders the iron available for growth.