The role of oxygen radicals in dye-mediated photodynamic effects in Escherichia coli B

Abstract

Photosensitive dyes representative of the thiazines, xanthenes, acridines, and phenazines mediated phototoxicity in Escherichia coli B. The observed phototoxicity was sensitizer-, light-, and oxygen-dependent and is therefore a photodynamic effect. Hydroxyl radical scavengers conferred protection against the photodynamic action of all of the representative dyes. The extent of protection was dependent on the concentration of scavenger and on the in vitro reactivity of the scavenger with the hydroxyl radical. Exogenous superoxide dismutase and catalase partially protected the cells against the dye-mediated phototoxicity, and prior induction of intracellular superoxide dismutase and catalase by growth in glucose minimal medium containing manganese and paraquat substantially protected E. coli B against the photodynamic action of all of the dyes examined. Combinations of protective treatments against the phototoxicity of all four classes of dyes, including superoxide dismutase and catalase preinduction and addition of extracellular superoxide dismutase and catalase or the addition of hydroxyl radical scavengers, provided nearly complete protection against the oxygen-dependent component of dye-mediated lethality. E. coli B grown in glucose minimal medium containing manganese and photosensitive dyes induced manganese superoxide dismutase. The extent of induction was correlated with the dyes' ability to photooxidize NADH in vitro. Thus, oxygen radicals are primarily responsible for the oxygen-dependent toxicity of the photosensitive dyes examined, and one adaptive response of E. coli B to a dye-mediated oxidative threat is to induce superoxide dismutase.