Dye-mediated photodynamic inactivation of <i>Bacillus subtilis </i>cells: Involvement of singlet oxygen and superoxide radicals

Abstract

Studies were carried out on the photodynamic inactivation of <i>Bacillus subtilis </i>cells by He-Ne laser irradiation in presence of methylene blue and toluidine blue. Electron paramagnetic resonance (EPR) measurements show decrease in the cell membrane nuidity due to photodynamic damage of the lipophilic compartments. Study of cell damage in presence of sodium azide, D₂O and glutathione as well as measurements on singlet oxygen/free radical generation by EPR show that with toluidine blue, singlet oxygen is the major reactive species leading to cell membrane damage. No free radical generation was observed in toluidine blue mediated photodamage. However, with methylene blue our observations suggest that the photodamage arises due to both singlet oxygen mediated membrane damage and intracellular damage by superoxide radical.