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

Abstract

It is important to know responses of the pathogenic fungi to reactive oxygen species by which hosts protect themselves against fungal infection. In the present study, sensitivities to the superoxide radical (O2-) and superoxide 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 O2- generator, paraquat (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 O2- generated extracellularly by photo-reduced riboflavin. There were no large differences in sensitivity to hydrogen peroxide in the two strains. Thus, the high tolerance of the mutant to PQ was suggested to result from low intracellular O2- generation by PQ due to the respiratory deficiency. It is generally accepted that fungal cells contain manganese (Mn)-SOD in the mitochondria and copper and zinc (CuZn)-SOD in the cytoplasm. Cyanide-insensitive SOD activity (attributable to Mn-SOD) was dominant in the parent strain throughout 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 on non-denaturing polyacrylamide gels. The electrophoretic profiles obtained were consistent with the results of the activity assay. These results showed that the respiratory deficiency affected oxidative stress sensitivity and SOD in C. albicans.

Deficiency in frataxin homologue YFH1 in the yeast Pichia guilliermondii leads to missregulation of iron acquisition and riboflavin biosynthesis and affects sulfate assimilation

“…6), namely, decreased activity of fast migrating form and significantly increased activity of the second form, may also suggest that cells of Δ yfh1 mutant are under oxidative stress. In favor of this assumption, the growth rate of Δ yfh1 mutant (but not of the parental wild-type strain) is significantly decreased in Burkholder synthetic medium supplemented with 200 mg/l of riboflavin which is a prooxidant under certain conditions (Ito-Kuwa et al 1999; Reddy et al 2008) (Fig. 7).…”

“…It is difficult to determine which enzyme is inactivated in the Δ yfh1 mutant since we found at least six putative homologues of SOD genes in the P. guilliermondii genome. Dramatic changes in SOD activity and increased level of iron accumulation, both could enhance sensitivity of Δ yfh1 mutants to riboflavin which is prooxidant when photo- or chemically reduced (Ito-Kuwa et al 1999; Reddy et al 2008). We did not illuminate plates or supplement media with a reducing agent in this experiment, since Δ yfh1 mutant cells itself possess high non-specific reductive activity toward different compounds including riboflavin which was converted to semi-reduced form (probably rhodoflavin) during growth of colonies (Fig.…”

“…On the other hand, P. guilliermondii wild-type cells do not possess active transport of riboflavin (Sibirny 1996). So, excretion and reduction of riboflavin which can be a source of superoxide anion causing oxidative stress and death of the cells, may be used to inhibit growth of competitor micro-organisms that have active transport of this vitamin (Ito-Kuwa et al 1999; Reddy et al 2008). Thus, several hypotheses have to be checked to explain interconnection between iron and riboflavin metabolism in flavinogenic yeasts.…”

“…SOD activity on a nondenaturing polyacrylamide gel was detected by negative staining (Ito-Kuwa et al 1999). The gel was washed twice in 50 mM phosphate buffer (pH 7.8) for 20 min.…”

Chemiluminescence of superoxide generated byCandida albicans: differential effects of the superoxide generator paraquat on a wild-type strain and a respiratory mutant

“…In a previous study, we compared O 2 ¡ sensitivity and superoxide dismutase (SOD) between a respirationcompetent wild-type parent strain (K) and a respiration-de cient mutant ( of Candida albicans [8]. Interestingly, the respiratory mutant was highly resistant to the herbicide paraquat (PQ) (1,1 0 -dimethyl-4,4 0 -bipyridinium dichloride), which is an intracellular O 2 ¡ generator, while both the parent and mutant strains exhibited a similar sensitivity to O 2 ¡ generated extracellularly by photo-reduced ribo avin.…”