Iron uptake and iron limited growth of Escherichia coli K-12

Cells of Escherichia coli K-12 could grow aerobically at an iron concentration as low as 0.05 micrometer without any of the known iron ionophores present. The growth rate increased between 0.05 and 2 micrometer iron. Supplementation with the iron ligands ferrichrome and citrate resulted in optimal growth already at 0.05 micrometer iron. Under certain conditions iron uptake preceded growth of cells by more than an hour. During logarithmic growth the rate of iron uptake matched the growth rate. The radioactive tracer method revealed a cellular iron content of 4 nmol/mg dry weight. After consumption of the iron in the medium cells continued to grow with high rate for 1-2 generations. The iron uptake activity was increased during iron starvation.