Effect of acid mine water on Escherichia coli: Structural Damage

Escherichia coli B/5 12-h cultures were exposed to filter-sterilized acid mine water (AMW), fixed in situ, and examined for morphological changes by transmission electron microscopy, scanning electron microscopy, and x-ray spectrometry. Thin sections showed that layers of the Gram-negative envelope were altered and often lacking. Additionally, polar regions of the cell were frequently devoid of cytoplasm. AMW-exposed cells were distorted and had an amorphous substance associated with them. Spectra obtained by x-ray spectrometry suggested that this amorphous substance was cytoplasm rather than a mineral precipitate from AMW. Morphometric analyses of control and AMW-exposed populations showed significant differences in mean volume, length, and width of cells stressed in AMW; this indicates that smaller cells were selectively destroyed by the action of AMW. We concluded that loss of cytoplasm and cell lysis were the consequence of AMW damage to the bacterial envelope.