Systematic study of parameters influencing the action of Rose Bengal with visible light on bacterial cells: Comparison between the biological effect and singlet-oxygen production

As part of a project to study different methods for the disinfection of eff luent water, the inactivation of different microorganisms (Escherichia coli , Deinococcus radiodurans and spores of Bacillus subtilis) using a combinat ion of a photosensitizer (Rose Bengal) with simulated sunlight and oxygen w as determined under various environmental conditions (temperature, pH index ). Zn parallel, the singlet-oxygen (O-1(2)) production was also measured un der the same conditions. Whereas the vegetative cells could be inactivated much more efficiently at increased temperature and altered index of pH, the production of O-1(2) remained essentially the same under these alterations . Additionally, the relations among the sensitivities of different cell typ es to be killed by our photodynamic treatments (PDT) were opposite to those found after exposure to ionizing radiation. The results of photodynamic ex periments do not reflect the cells' capacity to repair DNA strand breaks. S pares of B. subtilis, as a nonvegetative system, could not be inactivated b y illuminations up to 100 J cm(-1). Together, these findings indicate that DNA is not the primary target, the inactivation of which leads to the killi ng of our test organisms, instead, the cellular envelope appears to be the component being assaulted by our PDT.