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

Studies were carried but on the photodynamic inactivation of Bacillus subti lis cells by He-Ne laser irradiation in presence of methylene blue and tolu idine blue. Electron paramagnetic resonance (EPR) measurements show decreas e in the cell membrane fluidity due to photodynamic damage of the lipophili c compartments. Study of cell damage in presence of sodium azide, D2O and g lutathione as well as measurements on singlet oxygen/free radical generatio n by EPR show that with toluidine blue, singlet oxygen is the major reactiv e species leading to cell membrane damage. No free radical generation was o bserved in toluidine blue mediated photodamage. However, with methylene blu e our observations suggest that the photodamage arises due to both singlet oxygen mediated membrane damage and intracellular damage by superoxide radi cal.