  Iron is an essential trace-element for most organisms. However, because high
concentration of free intracellular iron is cytotoxic, cells have developed
complex regulatory networks that keep free intracellular iron concentration at
optimal range, allowing the incorporation of the metal into iron-using enzymes
and minimizing damage to the cell. We built a mathematical model of the network
that controls iron uptake and usage in the bacterium Escherichia coli to
explore the dynamics of iron flow. We simulate the effect of sudden decrease or
increase in the extracellular iron level on intracellular iron distribution.
Based on the results of simulations we discuss the possible roles of the small
RNA RyhB and the Fe-S cluster assembly systems in the optimal redistribution of
iron flows. We suggest that Fe-S cluster assembly is crucial to prevent the
accumulation of toxic levels of free intracellular iron when the environment
suddenly becomes iron rich.
