Oxidative stress sensitivity and superoxide dismutase of a wild-type parent strain and a respiratory mutant of Candida albicans

It is important to know responses of the pathogenic fungi to reactive oxyge n species by which hosts protect themselves against fungal infection. In th e present study, sensitivities to the superoxide radical (O-2(-)) and super oxide dismutase (SOD) were compared between a wild-type parent strain and a respiration-deficient mutant of Candida albicans. When their survival was examined on an agar medium containing an intracellular O-2(-) generator, pa raquat (PQ), the parent strain was selectively killed by increasing the PQ concentration. In contrast, when cells of both strains were illuminated in a riboflavin solution, they exhibited similar sensitivity to O-2(-) generat ed extracellularly by photo-reduced riboflavin. There were no large differe nces in sensitivity to hydrogen peroxide in the two strains. Thus, the high tolerance of the mutant to PQ was suggested to result from low intracellul ar O-2(-) generation by PQ due to the respiratory deficiency. It is general ly accepted that fungal cells contain manganese (Mn)-SOD in the mitochondri a and copper and zinc (CuZn)-SOD in the cytoplasm. Cyanide-insensitive SOD activity (attributable to Mn-SOD) was dominant in the parent strain through out growth phases, whereas cyanide-sensitive activity (attributable to CuZn -SOD) occurred in the mutant. The activity bands of Mn- and CuZn-SODs were clearly separated by electrophoresis of the cell extracts of both strains o n non-denaturing polyacrylamide gels. The electrophoretic profiles obtained were consistent with the results of the activity assay. These results show ed that the respiratory deficiency affected oxidative stress sensitivity an d SOD in C. albicans.