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.