SINGLE-STRAND BREAKS AND MUTAGENESIS IN YEAST INDUCED BY PHOTODYNAMICTREATMENT WITH CHLOROALUMINUM PHTHALOCYANINE

Photodynamic treatment of the yeast Kluyveromyces marxianus with the s ensitizer aluminum phthalocyanine results in loss of clonogenicity. In this paper the effect of this treatment on DNA of this yeast was inve stigated by searching for single strand breaks and forward mutations. Using the alkaline step elution technique it was found that illuminati on of the yeast in the presence of aluminum phthalocyanine resulted in an increase in single strand breaks. These could, partially, be repai red by post-incubating illuminated cells in growth medium. At comparab le survival levels, photodynamic treatment with aluminum phthalocyanin e induced fewer single strand breaks than X-ray treatment. By using a medium containing 5-fluoroorotic acid, mutants in the uracil biosynthe tic pathway were selected. Photodynamic treatment resulted in a light dose dependent increase of the mutation frequency. The observed mutage nicity of photodynamic treatment of the yeast with phthalocyanine was lower than the mutagenicity of UVC and X-ray treatment at equal colony forming capacity, indicating that photodynamic treatment is the least mutagenic of those treatments. It is concluded that photodynamic trea tment of K. marxianus results in DNA damage. Saccharomyces cerevisiae rad14 and rad52 mutants were used to determine the effect of the nucle otide excision repair and recombinational repair pathways, respectivel y, on survival after photodynamic treatment. Our data indicate that DN A damage is not the main determinant for cell killing by photodynamic treatment and that the type of damage induced is apparently not subjec t to RAD14- or RAD52 controlled repair. (C) 1997 Elsevier Science S.A.