Regulation of the unbalanced redox state in a Schizosaccharomyces pombe tert-butyl hydroperoxide-resistant mutant

The one-gene mutation in the tert-butyl hydroperoxide-resistant mutant hyd1-190 of the fission yeast Schizosaccharomyces pombe led to a 4-fold increase in resistance to t-BuOOH and decreased specific concentrations of superoxide and total thiols in comparison with the parental strain hyd+. It suggested an unbalanced redox state of the cells, which induced continuously increased specific activities of glutathione peroxidase, glutathione reductase and glutathione S-transferase and decreased activities of the antioxidant enzymes superoxide dismutases and glucose-6-phosphate dehydrogenase to regulate the redox balance of the mutation-induced permanent, low-level but tolerable internal stress. These results may contribute to the understanding of internal, oxidative stress-related human diseases.

Thermodynamic and kinetic processes during the unfolding of BSA in the presence of the mycotoxin patulin

The effects of the mycotoxin patulin on the thermodynamics and kinetics of the transition of bovine serum albumin (BSA) in aqueous solution were studied by Differential Scanning Calorimetry and Photoluminescence methods. Results show that in the presence of patulin, the free enthalpy change during the transition of BSA was decreased by an average of ∼ 46 kJ/mol, the free energy change was decreased by ∼ 4 kJ/mol, and the activation energy fell from ∼ 1546 to ∼ 840 kJ/mol. These results indicate that the bioactivity of patulin is based on the kinetic rather than on the thermodynamic properties of the transition. This is the first evidence of the direct interaction of patulin with the free thiol-containing BSA, a process which could contribute to the adverse cyto- and genotoxic effects induced by patulin.

In vivo direct interaction of the antibiotic primycin on a Candida albicans clinical isolate and its ergosterol-less mutant

Interaction of primycin antibiotic with plasma membrane, and its indirect biological effects were investigated in this study. The antifungal activity of primycin against 13 human pathogenic Candida ATCC and CBS reference species and 74 other Candida albicans clinical isolates was investigated with a microdilution technique. No primycin-resistant strain was detected. Direct interaction of primycin with the plasma membrane was demonstrated for the first time by using an ergosterol-producing strain 33erg+ and its ergosterol-less mutant erg-2. In growth inhibition tests, the 33erg+ strain proved to be more sensitive to primycin than its erg-2 mutant, indicating the importance of the plasma membrane composition in primycin-induced processes. The 64 μg ml-1 (56.8 nM) primycin treatment induced an enhanced membrane fluidity and altered plasma membrane dynamics, as measured by steady-state fluorescence anisotropy applying a trimethylammonium-diphenylhexatriene (TMA-DPH) fluorescence polarization probe. The following consequences were detected. The plasma membrane of the cells lost its barrier function, and the efflux of 260-nm-absorbing materials from treated cells of both strains was 1.5-1.8 times more than that for the control. Depending on the primycin concentration, the cells exhibited unipolar budding, pseudohyphae formation, and a rough cell surface visualized by scanning electron microscopy.

Characterization of stress processes of Phaffia rhodozyma stress-resistant mutant

A carotenoid-less Phaffia rhodozyma mutant (MCP 325) exhibited significantly higher resistance to oxidative stressors such as menadione, H2O2 and K2Cr2O7 than its astaxanthin-producing parental strain (MCP 324). The absence of carotenoids in the mutant did not explain this phenomenon. The cause of the decreased superoxide, hydroxyl radical and glutathione contents, the increased peroxide concentration and the elevated specific activity of catalase under uninduced conditions may be a second mutation. Peroxide treatment induced specific catalase activity in the mutant but not in the parental strain. Regulation of these processes led to the result that, in spite of the mutations, the two strains exhibited the same multiplication rate and generation time.

Pro-oxidative vs antioxidative properties of ascorbic acid in chromium(VI)-induced damage: an in vivo and in vitro approach

The effect of antioxidant ascorbic acid (vitamin C) pretreatment on chromium(VI)-induced damage was investigated using the yeast Saccharomyces cerevisiae as a model organism. The objective of this study was to pretreat yeast cells with the antioxidant ascorbic acid in an effort to increase cell tolerance against reactive chromium intermediates and reactive oxygen species formed during chromium(VI) reduction. Intracellular oxidation was estimated using the fluorescence indicators dihidro-2,7-dichlorofluorescein, dihydroethidium and dihydrorhodamine 123. The role of ascorbic acid pretreatment on chromium(VI) toxicity was determined by measuring mitotic gene conversion, reverse mutations, 8-OHdG, hydroxyl radical, superoxide anion and chromium(V) formation. The chromium content in the biomass was determined by flame atomic absorption spectrometry. In the absence of chromium, ascorbic acid effectively protected the cells against endogenous reactive oxygen species formed during normal cellular metabolism. In vitro measurements employing EPR and the results of supercoiled DNA cleavage revealed that the pro-oxidative action of ascorbic acid during Cr(VI) reduction was concentration-dependent and that harmful hydroxyl radical and Cr(V) had formed following Cr(VI) reduction. However, the in vivo results highlighted the important role of increased cytosol reduction capacity related to modification of Cr(V) formation, increased chromium accumulation, better scavenging ability of superoxide anions and hydrogen peroxide, and consequently decreased cytotoxicity and genotoxicity in ascorbic acid pretreated cells. Ascorbic acid influenced Cr(VI) toxicity both as a reducing agent, by decreasing Cr(V) persistence, and as an antioxidant, by decreasing intracellular superoxide anion and hydrogen peroxide formation and by quenching free radicals formed during Cr(VI) to Cr(III) reduction. Increased 8-OHdG and decreased reduced glutathione in ascorbic acid-treated cells might induce an endogenous antioxidant defense system and thus increase cell tolerance against subsequent Cr-induced stress.

The dose-dependent H2O2 stress response promotes increased survival forSchizosaccharomyces pombe cells expressing HIV-1 Vpr

Human immunodeficiency virus type 1 (HIV-1) viral protein R (Vpr) exerts multiple effects on viral and host cellular activities during infection, including induction of the cell cycle G2 arrest, and cell death in both human cells and the fission yeast Schizosaccharomyces pombe. We show that treament of exponential-phase wild-type Vpr-expressing S. pombe cells with a low, subinhibitory concentration (0.15 mmol/L) of hydrogen peroxide and 0.1 mmol/L thiamine significantly increased both cell proliferation and survival rates and decreased the number of elongated G2-arrested cells. Short-term, H2O2-induced adaptive stress increased the survival of the cells while acute stress conditions interrupted the Vpr-mediated death of the cells; however, no changes in cell length or cell phase were detected. The results suggest the importance of the oxidative status of the cells in Vpr-mediated processes. Our findings contribute to the development of a new approach via which to investigate the contribution of Vpr to HIV pathogenesis and to reduce the Vpr-mediated effects in HIV-infected patients.

Prevention of intracellular oxidation in yeast: the role of vitamin E analogue, Trolox (6-hydroxy-2,5,7,8-tetramethylkroman-2-carboxyl acid)

Reactive oxygen species (ROS) are not only generated in conditions of cellular stress but are also constitutively produced in most cell types by specific metabolic processes. This research focused on a potential antioxidant Trolox (model compound for alpha-tocopherol), with the aim to establish exact mechanisms of Trolox intracellular oxidation prevention on model organism Saccharomyces cerevisiae. Measuring intracellular oxidation of Trolox-treated yeast cells revealed that Trolox decreased intracellular oxidation during normal metabolism. Trolox treatment decreased cyto- and geno-toxicity of treated yeast cells in MES buffer, lowered intracellular oxidation, decreased intracellular peroxides formation, and increased H(2)O(2) degradation and superoxide quenching yeast extract ability. This study suggests that Trolox treatment provides prevention against intracellular ROS formation. Trolox application as therapeutic agent against intracellular ROS formation would be worth considering. Additionally, results indicate that yeasts are good model organisms for studying intracellular oxidation and oxidative stress. The obtained results on yeast cells might be useful to direct further human-related search for the Trolox evaluation as a human supplement used for protecting cells against intracellular free radical formation.

The transcription factor Pap1/Caf3 plays a central role in the determination of caffeine resistance in Schizosaccharomyces pombe

We previously identified four nuclear genes (caf1+-caf4+) in Schizosaccharomyces pombe, mutations in which confer resistance to caffeine and brefeldin A. caf1+, caf2+ and caf4+ were sequenced and found to be identical to the multidrug-resistance/stress-response genes hba1, crm1 and trr1, respectively. Here we show that caf3 is allelic to pap1, which encodes an AP-1-like transcription factor. The allele associated with caffeine resistance, caf3-89, contains a single-nucleotide exchange that results in a Leu-->Ser exchange in the NES (nuclear export signal) domain of the gene product. Due to this alteration, the modified protein can not be exported from the nucleus back into the cytoplasm, and thus accumulates in the nucleus. The activity of pap1/caf3 is shown to be necessary for manifestation of the caffeine resistance caused by mutations in the genes hba1/caf1 and crm1/caf2. We also cloned two genes that confer caffeine resistance when carried on a multicopy plasmid. One of them turned out to be a truncated allele of pad1/bfr2/sks1, which codes for a subunit of the 26 S proteosome. The putative product of the other gene, designated caf5, has a structure highly similar to that of MFS permeases. It contains two groups of six transmembrane spanning domains each, with the conserved motifs WRW, PET and GAIGGPVLGP in the fifth and sixth domains. These results are all consistent with our earlier hypothesis, which suggested that the caf genes are functionally interlinked in a complex detoxification mechanism. caf5 and pad1 may also encode parts of this mechanism.

Characterization of chromate-sensitive and -tolerant mutants of Schizosaccharomyces pombe

Stable chromium(VI)-sensitive and -tolerant mutants were obtained by induced mutagenesis of Schizosaccharomyces pombe lysine and leucine auxotrophic heterothallic strains 6chr+ and 9chr+. Eleven of them were selected for further studies. Fast transport of 51CrO4(2-) was detected in a representative sensitive mutant, chr-51S, while the tolerant mutant chr1-66T and the parental strain 6chr+ exhibited significantly lower 51CrO4(2-) uptake. The segregation of tetrads of three selected CrVI-tolerant mutants, chr1-66T, chr1-14T and chr2-04T, strongly indicated that tolerance was determined by single mutations. Random spore analysis proved that the mutations of chr1-66T and chr1-14T were allelic and the mutation of mutant chr2-04T was not allelic with the mutation of chr1-66T. Recombinants carrying the ura4D18 selective marker were created for transformation experiments. Two of them (chr1-661T and chr2-046T) can be used to clone and identify the genes responsible for their CrVI tolerance phenotype.

Characterization of Candida albicans colony morphological mutants and their hybrids by means of RAPD-PCR, isoenzyme analysis and pathogenicity analysis

A wild-type strain of Candida albicans (S1, ATCC 10261) was used to obtain stable auxotrophic colony morphological mutants (mutant M5 producing only true hyphae and mutant M2 containing 90 % blastospores and 10 % pseudohyphae) by induced mutagenesis. A hybrid was produced by somatic hybridization between these 2 mutants. Out of the isolated 10 clones, 2 stable hybrid clones were chosen and characterized: clone VI. 1M produced rough colonies containing a new, extended cell type (never observed in natural isolates), exhibited unipolar budding, did not form a germ tube, and possessed 12 chromosomal bands. All other features (antifungal and stress sensitivity, adhesion ability, pathogenicity, and isoenzyme and RAPD patterns) were similar to those of mycelial mutant M5. In contrast, the characteristics of clone VI.9S were similar to those of morphological mutant M2.

Characterization of Candida albicans colony-morphology mutants and their hybrids

The collection wild-type strain of Candida albicans was used to obtain auxotrophic and colony-morphology mutants by 'nitrosoguanidine' treatment. Intraspecific protoplast fusion induced by Ca(2+)-poly(ethyleneglycol) was carried out in various pairings between the auxotrophic strain producing smooth colonies and containing blastospores and the colony-morphology mutants containing a mixture of blastospores and pseudohyphae or only hyphae. Hybrids exhibiting full or partial complementation were obtained when mutants producing smooth colonies and colony-morphology variants of different origins were fused. The mutation responsible for the colony-morphology character (if various types of colony morphomutants were crossed) proved to be recessive or semidominant. Representative hybrids exhibited elevated DNA contents as measured by flow cytometry. To illustrate various cell types, and especially the intermediate one (never observed in natural isolates), a preparation method was further developed for scanning electron microscopic studies.

Variation of isoenzyme and RAPD patterns in Candida albicans morphological mutants with altered colony ultrastructure

Molecular typing methods were applied to characterize four stable morphological mutants [1] isolated from a UV-induced unstable mutant colony of Candida albicans. The wild-type strain (ATCC 64385), the intermediate unstable mutant and its four morphologically altered derivatives revealed the same electrophoretic karyotypes. Of the five isoenzymes tested (catalase, malate dehydrogenase, glutamate dehydrogenase, acid phosphatase and 3-glucosidase), glutamate dehydrogenase displayed a different enzyme pattern (with an extra band of lower mobility) in the morphological mutants. In contrast, the random amplification DNA polymorphism patterns of the mutant strains differed in all cases from that of the parental strain. Different primers revealed various degrees of DNA polymorphism; one of them (OPC-8) proved to be useful for differentiation between all examined strains. Differences in genetic alterations between spontaneous and induced mutants, and the applicability of different molecular markers to analyse the consequences of induced mutagenesis in C. albicans are discussed.

In vivo interaction of trivalent chromium with yeast plasma membrane, as revealed by EPR spectroscopy

The in vivo effects of CrCl(3) on an ergosterol-producing 33 erg(+) strain of the eukaryotic yeast Candida albicans, and on its ergosterol-deficient erg(-)2 mutant, were studied by using electron paramagnetic resonance spectroscopy. A 5-doxylstearic acid spin probe was applied to label the membranes. The absence of ergosterol, an increased accumulation of Delta(8) sterols, a decreased fatty acid chainlength and a lower proportion of unsaturated fatty acids of the erg(-)2 mutant resulted in a higher membrane rigidity and an increased sensitivity to Cr(III) than those of the parental 33 erg(+) strain. Cr(III) significantly increased the fluidity of the spin labelled membranes, this being more pronounced for the erg(-)2 mutant. The break in the slopes measured for the erg(-)2 mutant was decreased (DeltaAT approximately 4 degrees C) from 17 to 13 degrees C. Cr(III) treatment for 10 h caused a loss of metabolites adsorbing at 260 nm: this loss was 40% for 33 erg(+) and 60% for erg(-)2. This decriptification process might be the main cause of growth inhibition and cell killing by the impermeable Cr(III) ions.

Effect of hexavalent chromium on eukaryotic plasma membrane studied by EPR spectroscopy

The effect of Cr(VI) anion on an ergosterol-producing strain of eukaryotic yeast Candida albicans and its mutant with ergosterol-less membrane was studied with EPR spectroscopy. 5- and 14-doxyl stearic acid spin probes were used to label the protoplast membrane after removal of the cell wall. In control experiments, the mutant strain exhibited larger rigidity in the membrane than its parental strain. Addition of Cr(VI), at a minimum inhibitory concentration of 0.6 mM, increased the rotational mobility of the spin labels significantly and decreased the temperature of the structural changes in both strains, in the temperature range between 0 and 30 degrees C. The ergosterol-less mutant, having a membrane composition with increased polyunsaturated fatty acid content, exhibited higher Cr(VI) sensitivity. Treatment of the membrane with Cr(VI) for 10 min already resulted in an increase in membrane fluidity. An EPR signal of Cr(V) was detected which reached maximum amplitude after 120 min of treatment with Cr(VI). Further chemical reduction of Cr(V) in the absence of extracellular Cr(VI) led to a lack of detectable paramagnetic chromium intermediates within 200 min.

Hexavalent chromium uptake by sensitive and tolerant mutants of Schizosaccharomyces pombe

Lysine and leucine auxotrophic, heterothallic (h+, h-) strains of Schizosaccharomyces pombe were used to obtain chromium (VI)-sensitive and -tolerant mutants by ultraviolet radiation-induced and nitrosoguanidine-induced mutagenesis. The minimal inhibitory concentrations of K2Cr2O7 on YEA media were 225 microM for the wild-type strain CW-6, 125 microM for the sensitive mutant CS-6.51 and 275 microM for the tolerant mutant CT-6.66. The mutants exhibited cross-sensitivity of various patterns to Cd2+, Cu2+, Ni2+, Zn2+ and VO3-(4). Cr(VI) was added to the actively growing cultures and the total chromium (TOCr) content of the cells was determined. The sensitive mutant exhibited a high bioaccumulation ability, with a dry biomass of 810 micrograms g-1 after 30 min, while the tolerant mutant had a significantly lower ability than the wild-type strain. In PIPES buffer, washed, lysine-starved biomasses were treated with 75 microM Cr(VI) and after 2 h, the TOCr and the organically bound chromium (OBCr) were determined. Under these conditions, the sensitive and tolerant mutants had the same TOCr content, 50% of which was OBCr. The wild-type strain exhibited a lower TOCr content than that of its mutants and only 35% of this was OBCr. The Cr(VI)-sensitivity was due to a significantly increased uptake of Cr(VI).

Scanning electron microscopy characterisation of colonies of Candida albicans morphological mutants

The ultrastructures of colonies of two stable UV-induced morphological mutants and their parental strain of Candida albicans grown on glucose-containing solid medium were investigated by scanning electron microscopy. The structures and ultrastructures of these three types of colonies were determined not only in terms of the proportions of blastospores, hyphae and pseudohyphae, but also with regard to the mode of budding of blastospores and the positions of these particular cell types within the colonies. Hyphae with an atypical appearance and branching characters were observed both in regular-wrinkled and in irregular-wrinkled mutant colonies. Smooth colonies of the parental strain and the mutants exhibited the same hyphal network within the agar, suggesting that micro-environmental factors in the agar overcame the effects of these mutations.

Protoplast fusion hybrids of Candida albicans sterol mutants differing in nystatin resistance

Intraspecific protoplast fusion, induced by polyethylene glycol and Ca2+, was carried out in various pairings between auxotrophic nystatin-sensitive, ergosterol-producing strains of Candida albicans and their nystatin-resistant, ergosterol-less mutants of different origins. Nutritionally-complemented stable heterozygous diploid hybrids were obtained, which proved to be sensitive, semi-resistant or resistant to nystatin as a consequence of complementation or non-complementation for ergosterol biosynthesis. Dominant mutation control of the resistance was not found.

Freeze fracture electron microscopical investigation of Candida albicans cells sensitive and resistant to nystatin

A sterol mutant was isolated after nitrosoguanidine treatment, on the basis of th nystatin-resistant phenotypic behaviour, from a Candida albicans strain requiring adenine. The plasma membrane ultrastructure of the resistant mutant, observed by freeze-fracture electron microscopy, was not significantly different from the parental, ergosterol producing nystatin-sensitive strain. Nystatin treatment caused no ultrastructural change in the resistant strain, but led to the aggregation of membrane particles in the sensitive strain: this effect was considered to be the specific effect of nystatin. Other, probably nonspecific effects of nystatin on the sensitive strain were a deepening and deformation of invaginations, atypical membrane fracture, certain changes in the structure of cell wall and special ornamentation of its surface. No change in the intracellular membranes was observed.