Iron-Ion Concentration in Relation to Growth and Other Biological Processes

Studies on the growth of Chlorella sp. in culture solutions containing iron salts with sodium or potassium citrate in many different combinations indicate that iron is effective physiologically in the form of its ions. The total soluble iron may vary within wide limits and still have the same effect, either on growth or toxicity, providing the iron-ion concentration is the same. Certain observations point to the fact that some species of bacteria behave similarly. 2. The effect of citrates on growth in solutions containing a constant amount of total iron is paralleled by their effect on the relative iron-ion concentration as determined by chemical tests. 3. A theory relating iron-ion concentration to growth based on complex-ion formation has been developed which makes clear many problems involved in culture solution work, in the field and in biological phenomena in general. 4. The iron-ion concentration necessary for the growth of Chlorella is small. A provisional value at which growth may just take place has been calculated to be 1.47 x 10-6 gram ions. 5. It is suggested that the iron-ion concentration plays an important role in many physiological processes, especially those involving cell metabolism such as biological oxidations, and that these processes should be reconsidered in their relation to the iron-ion concentration rather than to the total iron.