PHOTODYNAMIC-ACTION OF PHYCOCYANIN - DAMAGE AND REPAIR

Phycocyanin extracted from the alga Spirulina platensis was used to se nsitize Escherichia coli strains (wild type and DNA repair mutants), S taphylococcus epidermidis (W5, wild type) and pBR322 plasmid DNA to vi sible light. The gram-positive Staphylococcus epidermidis and the plas mid pBR322 were found to be sensitive to the photodynamic action (PDA) of phycocyanin, but all strains of gram-negative E. coli proved to be resistant to the treatment. Experiments with a confocal laser scannin g microscope showed that phycocyanin binds to grampositive bacteria, b ut not to gram-negative E. coli. Inactivation of the cells and plasmid DNA was shown to depend on dye concentration, incubation time and tem perature. Survival of the pBR322 plasmid DNA after photosensitizing tr eatment with phycocyanin was not affected significantly in the single mutants deficient in either formamidopyrimidine-DNA-glycosylase (fpg-1 ) or UvrA endonuclease (uvrA) enzymes, but was greatly reduced in the double mutant uvrA fpg-1. The in vitro experiment showed that the pBR3 22 DNA damaged by phycocyanin PDA is a good substrate for the Fpg prot ein. As the Fpg protein plays an important role in the repair of DNA d amaged by photo-oxidative agents, it is suggested that phycocyanin PDA induces DNA photo-oxidation.