THE IN-VIVO EFFECTS OF ETHIDIUM-BROMIDE ON MITOCHONDRIAL AND RIBOSOMAL DNA IN CANDIDA-PARAPSILOSIS

The ability of Candida parapsilosis to grow in the presence of high le vels of ethidium bromide (EB) has been explored to study the effects o f this intercalating dye on DNA in vivo. By employing confocal microsc opy we have determined that EB penetrates the cellular membranes and b inds rapidly to the nucleolus, whereas mitochondrial DNA becomes stain ed after a longer exposure to this dye. No detectable staining of the nucleus has been detected under these conditions. Electrophoretic stud ies of both undigested and restricted DNAs confirm that the nuclear DN A is unaffected by high levels of EB, with the exception of the rDNA-b earing chromosome that undergoes significant structural alterations in the presence of EB. Moreover, the hybridization signal with the rDNA probe is proportionally reduced in samples obtained from cultures grow n in the presence of EB, suggesting that the average copy number of rR NA genes in these cultures may be affected. In striking contrast to ot her fungal species, the linear organelle genome in C. parapsilosis ret ains its structural and functional integrity in the presence of high c oncentrations of EB.