Persistence of caffeine effects on recA-cells. a Growth of E. coli JW2669-1 (recA-) when treated with 1.25 mg/mL MMS, 0.625 mg/mL caffeine, and MMS and caffeine co-treatment, in comparison with the growth of untreated cells. Morphology of E. coli recA-cells following inhibition assay. Treatment groups are no treatment (b), caffeine alone (c), MMS alone (d), and MMS and caffeine combined treatment (e). Arrows indicate cells displaying filamentous growth. Cells were observed at ×1,000 magnification. Pictures scales are 5 µm.