Figure 3.

Relationship between internal iron concentration and sensitivity to killing by H₂O₂. Cell concentrates of the congenic strains AB1157 (wild type), JI132 (SOD⁻), KK204 (Fur⁻), KK206 (bfr ftn), KK209 (SOD^- bfr ftn), KK216 (SOD⁻ Fur⁻), KK230 (SOD⁺ Edd overproducer), and KK231 (SOD⁻ Edd overproducer) were grown aerobically and assayed for internal iron by EPR. The sensitivity of the exponentially growing cultures to killing by exogenous H₂O₂ was determined after 8 min of exposure to 2.5 mM H₂O₂ in the same medium (8); other work has shown that the consequent cell death is due to iron-catalyzed DNA damage (52). Killing rates [-Ln(surviving fraction)/8] have been normalized to that of JI132 (8% survival). Error bars signify standard deviations of at least four independent experiments.