CO2 exacerbates oxygen toxicity.

Reactive oxygen species (ROS) are harmful because they can oxidize biological macromolecules. We show here that atmospheric CO(2) (concentration range studied: 40-1,000 p.p.m.) increases death rates due to H(2)O(2) stress in Escherichia coli in a dose-specific manner. This effect is correlated with an increase in H(2)O(2)-induced mutagenesis and, as shown by 8-oxo-guanine determinations in cells, DNA base oxidation rates. Moreover, the survival of mutants that are sensitive to aerobic conditions (Hpx(-) dps and recA fur), presumably because of their inability to tolerate ROS, seems to depend on CO(2) concentration. Thus, CO(2) exacerbates ROS toxicity by increasing oxidative cellular lesions.