The effects of zinc stress on the EPEC envelope imaged by transmission electron microscopy. After 10-hour growth in DMEM medium, cultures were grown for an additional 5 hours in the absence (A,B) and presence (D,E) of 0.3 mM zinc acetate. EPEC bacteria were pelleted, the medium discarded, and bacteria then were resuspended in 0.1 M MgSO4. Samples were placed on carbon formvar grids, stained with 1.3% uranyl acetate and viewed by transmission electron microscopy. The same procedure was repeated with 1-hour growth in DMEM medium, followed by an additional 5-hours of growth in the absence (C) and presence (F) of 0.3 mM zinc acetate. Arrow points to outer membrane blebs in (D). (A,D) Bars 1.0 μm; (B-C,D-F) Bars 0.1 μm.