The ability to acquire sufficient iron from the environment is essential for growth of most bacteria, including Escherichia coli and Shigella flexneri. In E. coli, the enterobactin-mediated iron acquisition system is the major way for the cells to get iron under iron-limiting conditions. Enterobactin is a siderophore that is synthesized and secreted in response to iron limitation to scavenge external ferric iron with high affinity. In this work, I showed that the alkyl hydroperoxide reductase (Ahp) system participates in cellular iron metabolism in both E. coli and S. flexneri. The Ahp system is composed of two proteins, AhpC and AhpF. AhpC detoxifies peroxides by converting peroxides to alcohol and water, and AhpF recycles AhpC. In this work, the data showed that the ahpC mutant synthesized and secreted much less enterobactin than the wild type E. coli and had a growth defect in low iron medium. AhpC influenced the first step of enterobactin biosynthesis by either facilitating the delivery of its substrate chorismate to the enterobactin biosynthesis pathway, or maintaining an optimal concentration of chorismate inside E. coli cells. In E. coli, the data showed that deletion of both ahpF and the glutathione reductase gor affected iron uptake or utilization, but not enterobactin biosynthesis, indicating the role of AhpF and Gor in cellular iron metabolism is different from that of AhpC. In S. flexneri, the Ahp system was also found to be involved in cellular iron metabolism; however, AhpC was not required for major steps of S. flexneri virulence: invasion, intracellular replication or cell-cell spread. Overall, the Ahp system participated in multiple steps of cellular iron metabolism. / text