Photosensitization of wild and mutant strains of Escherichia coli by meso-tetra (N-methyl-4-pyridyl)porphine

Wild type Escherichia coli cells as well as some mutant strains lacking spe cific DNA repair systems are efficiently billed upon visible light-irradiat ion after 5 min-incubation with meso tetra(4N-methyl-pyridyl) porphine (T4M PyP). The presence of oxygen is necessary for cell photoinactivation. The p orphyrin appears to exert its phototoxic activity largely by impairing some enzymic and transport functions at the level of both the outer and cytopla smic membrane. Thus, SDS-PAGE electrophoresis shows a gradual attenuation o f some transport protein bands as the irradiation proceeds, while a complet e loss of lactate and NADH dehydrogenase activities is caused by 15 min exp osure to light. On the other hand, DNA does not represent a critical target of T4MPyP photosensitization as suggested by the closely similar photosens itivity of the wild E. coli and E. coli strains defective for two different DNA repair mechanisms, as well as by the lack of any detectable alteration of the pUC19 plasmids extracted from photosensitized E. coli TG1 cells. (C ) 1999 Academic Press.