EFFECT OF IRON AND ZINC ON GROWTH PATTERNS OF ESCHERICHIA COLI IN IRON-DEFICIENT MEDIUM.

Ratledge, Colin (Medical Research Council of Ireland, Trinity College, Dublin, Ireland), and Frank G. Winder. Effect of iron and zinc on growth patterns of Escherichia coli in an iron-deficient medium. J. Bacteriol. 87:823-827. 1964.-Escherichia coli grew poorly in a shaken glycerol-salts medium depleted of trace metals. Normal growth was restored by the addition of 2.0 mug of iron per ml. At lower levels of iron, the lag period was increased and the rate of growth and the yield were decreased. Unless the initial concentration of iron was reduced below 0.035 mug/ml, the effect on the yield was comparatively small. Below this concentration, growth was approximately linear and the yield was proportional to the amount of iron present; these cultures underwent a second phase of growth about 24 hr after the original cessation of growth, the growth being slower than before and accompanied by increase in length of the bacteria. Zinc (0.10 mug/ml) was usually inhibitory during the first growth phase, but induced an earlier and more rapid second growth phase; it greatly increased the degree of filament formation. With a small inoculum (about 560 cells per ml) in depleted medium, the lag period was 1 day with 0.5 mug of iron per ml, but was 8 days when no additions were made.