Fig. 5

Current models for iron-dependent vs. iron-independent essential genes, in which the production of reactive oxygen species (ROS) is a critical component separating all essential genes into these two categories. When the protein function encoded by an iron-dependent essential gene is blocked, ROS is produced, contributing effective killing of bacterial cells in iron-replete conditions. However, ROS production would decrease in iron-restricted conditions (e.g. host tissues) reducing the killing activity and facilitating production of drug resistance bacteria via mutagenic action of sub-lethal concentration of ROS. On the contrary, blocking the protein function encoded by an iron-independent essential gene would lead to effective bacterial killing, regardless of the iron concentrations