No abstract

Escherichia coli, as most Gram‐negative bacteria, is insensitive to the photosensitizing action of both lipid‐soluble Zinc‐phthalocyanine (Zn‐Pc) and water‐soluble Zinc‐mono/disulfonated phthalocyanine (Zn‐PcS). Photosensitivity can be induced by alteration of the outer membrane, as obtained by either induction of competence or treatment with Tris‐EDTA. Both phthalocyanines largely bind at the level of the cytoplasmic membrane; however, Zn‐PcS shows a superior photosensitizing activity as compared with Zn‐Pc. Biochemical analyses performed on irradiated cells suggest that the cytoplasmic membrane is an important target of the photoprocess, while DNA is not involved.