FIG 1.

Effect of SOS inducers and inhibitors on hypermutation in vitro. Cultures of E. coli strains B171-8 and E22 grown overnight were subcultured into DMEM–F-12 broth medium and grown at 37°C with shaking at 300 rpm for 1.5 h, and the SOS-inducing drugs or metals were then added. The subcultures were collected at 4.5 h, and dilutions and plate counts were performed to measure total as well as antibiotic-resistant CFU per milliliter. Results are expressed as antibiotic resistance frequencies per 10⁷ total CFU. Abbreviations: zido, zidovudine; cipro, ciprofloxacin; zinc, zinc acetate. The definitions of symbols used are indicated in each panel.