The oxidative stress response of the yeastCandida intermedia to copper, zinc, and selenium exposure

Combined Proteomic and Metabolomic Analyses Reveal the Comprehensive Regulation of Stropharia rugosoannulata Mycelia Exposed to Cadmium Stress

The potential of Stropharia rugosoannulata as a microbial remediation material for cadmium (Cd)-contaminated soil lies in its capacity to absorb and accumulate Cd in its mycelia. This study utilized the TMT and LC-MS techniques to conduct integrated proteomic and metabolomic analyses with the aim of investigating the mycelial response mechanisms of S. rugosoannulata under low- and high-Cd stresses. The results revealed that mycelia employed a proactive defense mechanism to maintain their physiological functions, leading to reduced sensitivity to low-Cd stress. The ability of mycelia to withstand high levels of Cd stress was influenced primarily by the comprehensive regulation of six metabolic pathways, which led to a harmonious balance between nitrogen and carbohydrate metabolism and to reductions in oxidative stress and growth inhibition caused by Cd. The results provide valuable insights into the molecular mechanisms involved in the response of S. rugosoannulata mycelia to Cd stress.

Selenite bioreduction by a consortium of halophilic/halotolerant bacteria and/or yeasts in saline media

Selenium oxyanions are released into environments by natural and anthropogenic activities and are present in agricultural and glass manufacturing wastewater in several locations worldwide. Excessive amounts of this metalloid have adverse effects on the health of living organisms. Halophilic and halotolerant microorganisms were selected for selenium oxyanions remediation due to presence of significant amount of salt in selenium-containing wastewater. Effects of aeration, carbon sources, competitive electron acceptors, and reductase inhibitors were investigated on SeO₃^2- bio-removal. Additionally, NO₃^--containing wastewater were exploited to investigate SeO₃^2- remediation in synthetic agricultural effluents. The results showed that the SeO₃^2- removal extent is maximum in aerobic conditions with succinate as a carbon source. SO₄^2- and PO₄^3- do not significantly interfere with SeO₃^2- reduction, while WO₄^2- and TeO₃^2- decrease the SeO₃^2- removal percentage (up to 35 and 37%, respectively). Furthermore, NO₃^- had an adverse effect on SeO₃^2- biotransformation by our consortia. All consortia reduced SeO₃^2- in synthetic agricultural wastewaters with a 45-53% removal within 120 h. This study suggests that consortia of halophilic/halotolerant bacteria and yeasts could be applied to treat SeO₃^2--contaminated drainage water. In addition, sulphates, and phosphates do not interfere with selenite bioreduction by these consortia, which makes them suitable candidates for the bioremediation of selenium-containing wastewater.

Integrated physiologic and proteomic analysis of Stropharia rugosoannulata mycelia in response to Cd stress

Soil Cd pollution seriously threatens environment and human health. Due to its ability to absorb and accumulate Cd in mycelia, Stropharia rugosoannulata could be a potential candidate for bioremediation of Cd-contaminated soils; however, the response mechanism of mycelia to Cd stress is still unclear. In this study, the physiologic and proteomic differences of S. rugosoannulata mycelia under 0.2 mg/L (low) and 2 mg/L (high) Cd stress were investigated. The results showed that Cd accumulation and mycelial growth inhibition exhibited a concentration-depended trend. Analysis of antioxidant system indicated that SOD, GR, GSH, GSSG and ASA played key roles in resisting the toxic effects of Cd. Via proteome analysis, 24 and 267 differentially expressed proteins (DEPs) were observed under low and high Cd stress, respectively. GO and KEGG analysis found that the mycelial growth inhibition might due to the down-regulation of some DEPs involved in "valine, leucine and isoleucine biosynthesis" and "tyrosine metabolism"; the certain tolerance to high Cd stress might attribute to the regulation of DEPs referred to energy metabolism and antioxidant system-related pathways, maintaining cellular energy homeostasis and removing ROS. These results provide a theoretical basis for further elucidation of response mechanisms in S. rugosoannulata to Cd stress.

Metabolic Response of the Yeast Candida utilis During Enrichment in Selenium

Selenium (Se) was found to inhibit the growth of the yeast Candida utilis ATCC 9950. Cells cultured in 30 mg selenite/L supplemented medium could bind 1368 µg Se/g of dry weight in their structures. Increased accumulation of trehalose and glycogen was observed, which indicated cell response to stress conditions. The activity of antioxidative enzymes (glutathione peroxidase, glutathione reductase, thioredoxin reductase, and glutathione S-transferase) was significantly higher than that of the control without Se addition. Most Se was bound to water-insoluble protein fraction; in addition, the yeast produced 20–30 nm Se nanoparticles (SeNPs). Part of Se was metabolized to selenomethionine (10%) and selenocysteine (20%). The HPLC-ESI-Orbitrap MS analysis showed the presence of five Se compounds combined with glutathione in the yeast. The obtained results form the basis for further research on the mechanisms of Se metabolism in yeast cells.

Antimicrobial Activity of Different Artemisia Essential Oil Formulations

The extreme lipophilicity of essential oils (EOs) impedes the measurement of their biological actions in an aqueous environment. We formulated oil in water type Pickering Artemisiaannua EO nanoemulsions (AEP) with surface-modified Stöber silica nanoparticles (20 nm) as the stabilizing agent. The antimicrobial activity of AEP and its effects on mature Candida biofilms were compared with those of Tween 80 stabilized emulsion (AET) and ethanolic solution (AEE) of the Artemisia EO. The antimicrobial activity was evaluated by using the minimum inhibitory concentrations (MIC₉₀) and minimum effective concentrations (MEC₁₀) of the compounds. On planktonic bacterial and fungal cells beside growth inhibition, colony formation (CFU/mL), metabolic activity, viability, intracellular ATP/total protein (ATP/TP), along with reactive oxygen species (ROS) were also studied. Artemisiaannua EO nanoemulsion (AEP) showed significantly higher antimicrobial activity than AET and AEE. Artemisiaannua EO nanoemulsions (AEP) generated superoxide anion and peroxides-related oxidative stress, which might be the underlying mode of action of the Artemisia EO. Unilamellar liposomes, as a cellular model, were used to examine the delivery efficacy of the EO of our tested formulations. We could demonstrate higher effectiveness of AEP in the EO components’ donation compared to AET and AEE. Our data suggest the superiority of the AEP formulation against microbial infections.

Cytotoxic Action of Artemisinin and Scopoletin on Planktonic Forms and on Biofilms of Candida Species

We investigated the antifungal activities of purified plant metabolites artemisinin (Ar) and scopoletin (Sc) including inhibition, effects on metabolic activities, viability, and oxidative stress on planktonic forms and on preformed biofilms of seven Candida species. The characteristic minimum inhibitory concentration (MIC90) of Ar and Sc against Candida species ranged from 21.83-142.1 µg/mL and 67.22-119.4 µg/mL, respectively. Drug concentrations causing ≈10% CFU decrease within 60 minutes of treatments were also determined (minimum effective concentration, MEC10) using 100-fold higher CFUs than in the case of MIC90 studies. Cytotoxic effects on planktonic and on mature biofilms of Candida species at MEC10 concentrations were further evaluated with fluorescent live/dead discrimination techniques. Candida glabrata, Candida guilliermondii, and Candida parapsilosis were the species most sensitive to Ar and Sc. Ar and Sc were also found to promote the accumulation of intracellular reactive oxygen species (ROS) by increasing oxidative stress at their respective MEC10 concentrations against the tested planktonic Candida species. Ar and Sc possess dose-dependent antifungal action but the underlying mechanism type (fungistatic and fungicidal) is not clear yet. Our data suggest that Ar and Sc found in herbal plants might have potential usage in the fight against Candida biofilms.

Antimicrobial Activity of Chamomile Essential Oil: Effect of Different Formulations

Essential oils (EOs) are highly lipophilic, which makes the measurement of their biological action difficult in an aqueous environment. We formulated a Pickering nanoemulsion of chamomile EO (C_Pe). Surface-modified Stöber silica nanoparticles (20 nm) were prepared and used as a stabilizing agent of C_Pe. The antimicrobial activity of C_Pe was compared with that of emulsion stabilized with Tween 80 (C_T80) and ethanolic solution (C_Et). The antimicrobial effects were assessed by their minimum inhibitory concentration (MIC₉₀) and minimum effective (MEC₁₀) concentrations. Besides growth inhibition (CFU/mL), the metabolic activity and viability of Gram-positive and Gram-negative bacteria as well as Candida species, in addition to the generation of oxygen free radical species (ROS), were studied. We followed the killing activity of C_Pe and analyzed the efficiency of the EO delivery for examined formulations by using unilamellar liposomes as a cellular model. C_Pe showed significantly higher antibacterial and antifungal activities than C_T80 and C_Et. Chamomile EOs generated superoxide anion and peroxide related oxidative stress which might be the major mode of action of Ch essential oil. We could also demonstrate that C_Pe was the most effective in donation of the active EO components when compared with C_T80 and C_Et. Our data suggest that C_Pe formulation is useful in the fight against microbial infections.

Effect of selenium on growth and antioxidative system of yeast cells

Selenium exhibits health-promoting properties in humans and animals. Therefore, the development of selenium-enriched dietary supplements has been growing worldwide. However, it may also exhibit toxicity at higher concentrations, causing increased oxidative stress. Different species of yeasts may exhibit different tolerances toward selenium. Therefore, in this study, we aimed to determine the effect of selenium on growth and on the antioxidative system in Candida utilis ATCC 9950 and Saccharomyces cerevisiae ATCC MYA-2200 yeast cells. The results of this study have demonstrated that high doses of selenium causes oxidative stress in yeasts, thereby increasing the process of lipid peroxidation. In addition, we obtained an increased level of GSSG from aqueous solutions of yeast biomass grown with selenium supplementation (40-60 mg/L). Increased levels of selenium in aqueous solutions resulted in an increase in the activity of antioxidant enzymes, including glutathione peroxidase and glutathione reductase. These results should encourage future research on the possibility of a thorough understanding of antioxidant system functioning in yeast cells.

Expression patterns of SRB1 and other stress-related genes in Candida albicans under oxidative, hyperosmotic and thermal stress

Candida albicans, a human fungal pathogen, is able to tolerate certain levels of environmental stresses. Its cell wall plays an important role in cellular homeostasis, responding to environmental stimuli. SRB1 gene encodes a GDP-mannose pyrophosphorylase that catalyzes the formation of the major cell wall component, mannan. The exact relationship between SRB1 and various stresses is not yet fully understood. In current study, C. albicans SC5314 cells were exposed to oxidative, hyperosmotic, and thermal stresses. The expression of SRB1 and related stress response genes, HOG1, CAP1, MKC1, and HSP90, was systematically evaluated in cells exposed to various levels of stress. In addition, the apoptosis and ultrastructural changes of the cells were examined. We found that the expression of SRB1 and related stress response genes significantly increased under oxidative, hyperosmotic, and thermal stresses, and the increased gene expression was correlated with higher percentages of apoptosis and ultrastructural changes in C. albicans cells. We propose that protein glycosylation is associated with stress response that involves SRB1 in C. albicans. Further in-depth studies of SRB1 function should aid our understanding of C. albicans pathogenesis, and provide important clues about the development of novel antifungal compounds for drug resistant C. albicans.

Exploring the fungal protein cadre in the biosynthesis of PbSe quantum dots

While a large number of microbial sources have recently emerged as potent sources for biosynthesis of chalcogenide quantum dots (QDs), studies regarding their biomimetic strategies that initiate QD biosynthesis are scarce. The present study describes several mechanistic aspects of PbSe QD biosynthesis using marine Aspergillus terreus. Scanning electron microscopic (SEM) studies indicated distinctive morphological features such as abrasion and agglomeration on the fungal biomass after the biosynthesis reaction. Further, the biomass subsequent to the heavy metal/metalloid precursor was characterized with spectral signatures typical to primary and secondary stress factors such as thiol compounds and oxalic acid using Fourier Transform Infra-Red Spectroscopic (FTIR) analysis. An increase in the total protein content in the reaction mixture after biosynthesis was another noteworthy observation. Further, metal-phytochelatins were identified as the prominent metal-ion trafficking components in the reaction mixture using Liquid Chromatography Mass Spectroscopic analysis (LCMS). Subsequent assays confirmed the involvement of metal binding peptides namely metallothioneins and other anti-oxidant enzymes that might have played a prominent role in the microbial metal detoxification system for the biosynthesis of PbSe QDs. Based on these findings a possible mechanism for the biosynthesis of PbSe QDs by marine A. terreus has been elucidated.

Effects of copper on induction of thiol-compounds and antioxidant enzymes by the fruiting body of Oudemansiella radicata

Oudemansiella radicata has been found to have ability to tolerate and accumulate heavy metals. In this study, to know about the metal tolerance and detoxification strategy of O. radicata, the tolerance responses in both cap and stipe of the fruiting body, including the copper content, the changes of thiol compounds production and antioxidant enzymes activities, caused by various copper stress (150-600 mg kg(-1)) during 2-6 days were investigated. Results showed that Cu content in the fruiting bodies increased with the increasing Cu concentrations and growing time, which was higher in cap than that in stipe. For thiols contents, the maximum level was in the sample at 300 mg kg(-1) Cu after 2 d both in cap and stipe, in accordance with superoxide dismutase (SOD) and glutathione reductase (GR) activities. Guaicol peroxidase (POD) activities reached maximum at 150 mg kg(-1) Cu after 4 d and 6 d, respectively in cap and stipe, while the maximum of catalase (CAT) activities was recorded at 300 and 600 mg kg(-1) Cu after 4 d in the cap and stipe, respectively. As a whole, low concentration of Cu stimulated the production of thiols and activated the antioxidant enzymes activities in the fruiting body of O. radicata after 2/4 d, while high-level Cu decreased the thiols production and enzymes activities after 4/6 d. Furthermore, the cap was more sensitive than the stipe to Cu exposure. Different indicators showed different responses to copper accumulation and the different fruiting part (cap and stipe) of O. radicata had ability to response the oxidative stress caused by Cu. Considering the metal accumulation and its own detoxification with short growing time, mushroom might have the potential to be used as bio-accumulator to deal with Cu exposure in the Cu-contaminated farmland soil.

Oxidative stress, glutathione level and antioxidant response to heavy metals in multi-resistant pathogen, Candida tropicalis

In this study, we explored the multiple heavy metal-resistant yeast isolated from heavy metal-polluted environment. The isolated yeast showed maximum growth at 30 °C, pH 7.0, and the strain was identified as Candida tropicalis through 18S ribosomal RNA (rRNA) gene sequence analysis. Yeast cells grew well in medium containing different concentrations of heavy metal ions [CdCl₂, Pb(NO₃)₂, NaAsO₂, CuSO₄ and K₂Cr₂O₇]. Minimum inhibitory concentration (MIC) against different metal ions was ranged from 5 to 19 mM, and the metal resistance value against each metal observed by yeast cells was 5 mM (Cr), 10 mM (Cd), 15 mM (As), 14 mM (Cu) and 19 mM (Pb) and increased in the following order: Pb > Cu > As ≥ Cd > Cr. The total cellular glutathione, GSH/GSSG redox couple and metallothioneins like protein (MT) were assayed by growing cultures for 24 h and exposed to 100 mg/L of each heavy metal ion. Remarkable increase in γ-glutamylcysteinylglycine (GSH) level was determined in arsenic and cadmium treatment followed by chromium, lead and copper. Stressed cells had much more oxidized GSH than unstressed cells. GSH/GSSG ratio was significantly increased in cadmium and copper treatment in contrast to chromium, arsenic and lead. Statistical analysis revealed significantly higher cysteine level in all metal-treated samples as compared to control. Antioxidant glutathione transferase activity was not detected in metal-treated and untreated yeast samples. One-dimensional electrophoresis of proteins revealed marked differences in banding pattern of heavy metal-exposed yeast samples. A prominent 20 kDa band was observed in all treated samples suggesting that some differential proteins could be over-expressed during heavy metal treatment and might be involved in cell resistance mechanisms.

Identification of cadmium-resistant fungi related to Cd transportation in bermudagrass [Cynodon dactylon (L.) Pers]

Phytoremediation utilizing plants and microbes has been increasingly adopted as a green technology for cleaning up heavy metal polluted soils. Cd polluted soil and native bermudagrass from Liuyang and Zhuzhou in Hunan province of China were collected to investigate microbial diversity and isolate Cd resistant fungi, and then to determine the effect of Cd resistant fungi on Cd tolerance and transportation of bermudagrass. The functional diversity of microorganisms was evaluated using the BIOLOG Eco method. Cd-resistant fungi strain was isolated and identified as Aspergillus aculeatus based on the ribosomal internal transcribed spacer region sequence analysis. Bermudagrass was exposed to control, Cd only, and Cd plus A. aculeatus (Cd + A. aculeatus) with growth matrix (sawdust/sand = 3/1 in volume). Results indicated that Cd + A. aculeatus treated bermudagrass exhibited a higher photosynthetic activity compared to Cd only treated plants. Inoculation of A. aculeatus resulted in a decrease in stem and leaf Cd concentrations, to a greater extent for Cd-sensitive than for Cd-tolerant genotype. However, inoculation of A. aculeatus increased root Cd concentration under Cd stress conditions, significantly elevated soil pH, and decreased soil water-soluble Cd concentration. These results suggested that A. aculeatus might be potentially applied to improve Cd tolerance and to reduce Cd transportation to shoot of bermudagrass.

tert-Butyl hydroperoxide-induced differing plasma membrane and oxidative stress processes in yeast strains BY4741 and erg5Δ

The molecular mechanism of tert-butyl hydroperoxide (t-BuOOH) elicited cytotoxicity and the background of t-BuOOH sensitivity were studied in the Saccharomyces cerevisiae ergosterol-less gene deletion mutant erg5Δ and its parental strain BY4741. In comparison to BY4741, untreated erg5Δ cells exhibited alterations in sterol and fatty acid compositions of the plasma membrane, as reflected by the inherent amphotericin B resistance, an elevated level (31%) of plasma membrane rigidity and a decreased uptake of glycerol. Surprisingly, the untreated erg5Δ cells exhibited an unbalanced intracellular redox state, accompanied by the continuous upregulation of the antioxidant enzymes Mn superoxide dismutase, catalase, and glutathione S-transferase, which resulted in decreased specific concentrations of superoxide and peroxides and elevated levels of the hydroxyl radical and thiols. The 2.5-fold sensitivity of erg5Δ to t-BuOOH suggested that the oxidative stress adaptation processes of the mutant could not restore the redox homeostasis of the cells and there is an overlap between sterol and redox homeostases. t-BuOOH treatment of both strains induced adaptive modification of the sterol and fatty acid compositions, increased the plasma membrane fluidity and elevated the specific activities of most antioxidant enzymes through specific regulation processes in a strain-dependent manner.

The use of multiple endpoints to assess cellular responses to environmental contaminants in the interstitial marine ciliate Euplotes crassus

This paper presents the results of investigations on the suitability of Euplotes crassus, an interstitial marine ciliate, to be used as model organism in ecotoxicology and thereafter to evaluate the toxicity of estuarine and coastal sediments upon laboratory exposure. Nowadays, anthropogenic activities have resulted in accumulation of metals and organic pollutants in the environment as well as in the food chain hence leading to serious ecological and human health problems. This may pose a risk to benthic and epibenthic organisms and it is crucial to discover toxicity tests that will identify adverse effects of sediment-associated chemicals on benthic organisms. Due to their nature as a eukaryotic cell/organism and their position in the food web, ciliated protozoa are suitable models for evaluating the effects of pollution on aquatic communities. Lethal and sublethal effects of exposure to inorganic and organic pollutants were tested on the cell mortality, replication rate, lysosomal membrane stability and endocytosis rate of E. crassus. Increasing nominal concentrations of individual and mixtures of mercury, copper, and benzo(a)pyrene were investigated in this study as they might be bioavailable in naturally occurring polluted sites. A significant decrease in the mean replication rate (p<0.05) was found after 24h exposures to m/μM concentrations of all tested pollutants. At the same time, significant decreases of lysosomal membrane stability (p<0.05) were observed for Cu (5 μM), Hg (10 nM), and B(a)P (200 nM). Among the entire suite of tests, endocytosis rate test demonstrated the highest sensitivity. Exposures to binary mixtures of all studied pollutants were performed showing both inorganic-organic and inorganic-inorganic additive and/or antagonist effects. Moreover, medium salinity was also varied to mimic estuarine-like environmental conditions linking biological response to ionic strengths. Under these conditions significant increases of both endocytosis rate and lysosomal membrane stability were observed and related to the increment of some Hg- and Cu-related toxic complexes. The studied biomarkers were always able to discriminate between the effects of organic and inorganic pollutants. Together with the short time and simplicity of the test procedures, results obtained in this study indicate that E. crassus is a promising and convenient bioindicator for evaluating the toxicity of different environmental matrixes like pore water, sediments and wastewaters--polluted by metals and organic pollutants.

Effects of heavy metals on production of thiol compounds and antioxidant enzymes in Agaricus bisporus

In a pre-experiment, Agaricus bisporus mycelia grown in PDL medium were found to have a substantial ability to tolerate and accumulate heavy metals. In the study, we investigated changes in the contents of soluble protein and thiol compounds as well as the activities of antioxidant enzymes caused by copper, zinc, lead, and cadmium (nitrate salts) in mycelia of A. bisporus during short-and long-term exposure. Results showed that high-level metal concentrations significantly decrease the contents of soluble protein after long-term exposure, Cu and Zn concentrations significantly increase the thiol compounds levels after long-term exposure, while high-level Cd significantly decrease thiol compounds after long-term exposure. Additionally, SOD activities were significantly increased after long-term exposure to metals, especially to Cd. The CAT activities were enhanced after long-term exposure to low-level Cu and high-level Zn, and enhanced after short-and long-term exposure to high-level Pb. The POD activities were significantly increased after long-term exposure to metals, and increased after short-term exposure to Cd and high-level Pb.

The abc1-/coq8- respiratory-deficient mutant of Schizosaccharomyces pombe suffers from glutathione underproduction and hyperaccumulates Cd2+

The abc1(-)/coq8(-) gene deletion respiratory-deficient mutant NBp17 of fission yeast Schizosaccharomyces pombe displayed a phenotypic fermentation pattern with enhanced production of glycerol and acetate, and also possessed oxidative stress-sensitive phenotypes to H(2)O(2), menadione, tBuOOH, Cd(2+), and chromate in comparison with its parental respiratory-competent strain HNT. As a consequence of internal stress-inducing mutation, adaptation processes to restore the redox homeostasis of mutant NBp17 cells were detected in minimal glucose medium. Mutant NBp17 produced significantly increased amounts of O(2)•- and H(2)O(2) as a result of the decreased internal glutathione concentration and the only slightly increased glutathione reductase activity. The Cr(VI) reduction capacity and hence the •OH production ability were decreased. The mutant cells demonstrated increased specific activities of superoxide dismutases and glutathione reductase (but not catalase) to detoxify at least partially the overproduction of reactive oxygen species. All these features may be explained by the decreased redox capacity of the mutant cells. Most notably, mutant NBp17 hyperaccumulated yellow CdS.

A PLAC8-containing protein from an endomycorrhizal fungus confers cadmium resistance to yeast cells by interacting with Mlh3p

Cadmium is a genotoxic pollutant known to target proteins that are involved in DNA repair and in antioxidant defence, altering their functions and ultimately causing mutagenic and carcinogenic effects. We have identified a PLAC8 domain-containing protein, named OmFCR, by a yeast functional screen aimed at identifying genes involved in cadmium resistance in the endomycorrhizal fungus Oidiodendron maius. OmFCR shows a remarkable specificity in mediating cadmium resistance. Both its function and its nuclear localization in yeast strictly depend on the interaction with Mlh3p, a subunit of the mismatch repair (MMR) system. Although proteins belonging to the PLAC8 family are widespread in eukaryotes, they are poorly characterized and their biological role still remains elusive. Our work represents the first report about the potential role of a PLAC8 protein in physically coupling DNA lesion recognition by the MMR system to appropriate effectors that affect cell cycle checkpoint pathways. On the basis of cell survival assays and yeast growth curves, we hypothesize that, upon cadmium exposure, OmFCR might promote a higher rate of cell division as compared to control cells.

Multiple metal tolerance and biosorption of cadmium by Candida tropicalis isolated from industrial effluents: glutathione as detoxifying agent

The ability of cadmium uptake by metal-resistant yeast, Candida tropicalis, from the liquid medium and wastewater was evaluated. The minimum inhibitory concentration of Cd(2+) against C. tropicalis was 2,500 mg L(-1). The yeast also showed tolerance toward Zn(2+) (1,400 mg L(-1)), Ni(2+) (1,000 mg L(-1)), Hg(2+) (1,400 mg L(-1)), Cu(2+) (1,000 mg L(-1)), Cr(6+) (1,200 mg L(-1)), and Pb(2+) (1,000 mg L(-1)). The yeast isolate showed typical growth curves, but lag and log phases extended in the presence of cadmium. The yeast isolate showed optimum growth at 30°C and pH 8. The metal processing ability of the isolate was determined in a medium containing 100 mg L(-1) of Cd(2+). C. tropicalis could decline Cd(2+) 70%, 85%, and 92% from the medium after 48, 96, and 144 h, respectively. C. tropicalis was also able to remove Cd(2+) 40% and 78% from the wastewater after 6 and 12 days, respectively. Cd produced an increase in glutathione (GSH) and nonprotein thiol levels by 135% and 134% at 100-mg L(-1) concentration, respectively. An increase in the synthesis of GSH is involved in metal tolerance, and the presence of increasing GSH concentrations may be a marker for high metal stress in C. tropicalis. C. tropicalis, which is resistant to heavy metal ions and is adaptable to the local environmental conditions, may be employed for metal detoxification operations.

Serum levels of Cu, Se, and Zn in adult rural/urban residents in Ghana: paradigm shift?

Deficiencies in Cu, Se, and Zn impair one or more biochemical functions, and excess are associated with toxicity. Baseline studies on the Ghanaian population are scanty. The study was undertaken to determine whether significant rural/urban differences in the serum levels of Cu, Se, and Zn did exist. Forty males/60 females from rural and 50 males/50 females from urban Ghanaian communities were sampled. Serum Cu, Se, and Zn were determined using flame atomic absorption spectrometry. Cu level for rural and urban subjects was 997 +/- 333 and 979 +/- 290 microg/L, respectively (p = 0.68). However, Cu levels were significantly higher in the rural females (1,063 +/- 367 microg/L) than the rural males (898 +/- 249 microg/L; p = 0.0085). Se levels for rural/urban subjects were 97 +/- 36 and 87 +/- 31 microg/L, respectively (p = 0.03). Zn levels in the rural/urban subjects were 312 +/- 218 and 150 +/- 102 microg/L, respectively (p = 0.002). Additionally, Zn was significantly higher in rural females (428 +/- 204 microg/L) than the urban females (166 +/- 103 microg/L; p = 0.0002). Finally, Zn was significantly higher in rural females (428 +/- 204 microg/L) than males (172 +/- 116 microg/L; p = 0.0028). In conclusion, Cu, Se, and Zn were higher in the rural group compared to the urban group, and the generally low Zn levels were confirmed in another cohort follow-up study.

Phagocytic activity, respiratory burst, cytoplasmic free-Ca(2+) concentration and apoptotic cell ratio of haemocytes from the black tiger shrimp, Penaeus monodon under acute copper stress

The aim of this study was to investigate the cellular toxicity of copper-induced injury to the black tiger shrimp Penaeus monodon. The 24h, 48h, 72h and 96h LC(50) (median lethal concentration) of Cu(2+) on P. monodon (11.63+/-1.14g) were found to be 3.49, 1.54, 0.73 and 0.40mgL(-1), respectively. Total haemocyte count (THC), phagocytic activity, respiratory burst (RB), cytoplasmic free-Ca(2+) (cf-Ca(2+)) concentration and apoptotic cell ratio of shrimp were determined after exposure to different concentrations of Cu(2+) (0, 0.05, 0.5, 1.5 and 3.5mgL(-1)) for 0, 6, 12, 24 and 48h. There was no significant effect on the analytic indicator of shrimp exposed to 0.05mgL(-1) Cu(2+). THC decreased after Cu-exposure to 0.5mgL(-1) for 48h, 1.5mgL(-1) for 24h and 3.5mgL(-1) for 12h. Phagocytic activity decreased in P. monodon following 48h exposure to 3.5mgL(-1) Cu(2+). RB was induced after 6h exposure to 0.5, 1.5 and 3.5mgL(-1) Cu(2+). cf-Ca(2+) concentration increased after 48h exposure to 0.5mgL(-1) Cu(2+), and 12h exposure to 1.5 and 3.5mgL(-1) Cu(2+). The percentage of apoptotic cells increased to 9.5%, 16.3% and 18.6% respectively following 48h exposure to 0.5, 1.5 and 3.5mgL(-1) Cu(2+). These results indicate that Cu can induce oxidative stress, elevation of cf-Ca(2+) and cell apoptosis, and inhibit phagocytic activity in the shrimp P. monodon, and the lethal injury of Cu(2+) to P. monodon may be mainly due to the sharp reduction of THC caused by ROS-induced apoptosis.

SOD1-targeted gene disruption in the ericoid mycorrhizal fungus Oidiodendron maius reduces conidiation and the capacity for mycorrhization

The genome sequences of mycorrhizal fungi will provide new opportunities for studying the biology and the evolution underlying this symbiotic lifestyle. The generation of null mutants at the wild-type loci is one of the best methods for gene-function assignment in the post-genomic era. To our knowledge, the generation of superoxide dismutase 1 (SOD1)-null mutants in the ericoid mycorrhizal fungus Oidiodendron maius is the first example of a gene-targeted disruption via homologous recombination in a mycorrhizal fungus. The disruption of OmSOD1 by Agrobacterium-mediated transformation resulted in the presence of oxidative stress markers, even in the absence of external superimposed stresses, and an increased sensitivity to reactive oxygen species (ROS)-generating substances, especially to menadione. A reduction in conidiation and in the percentage of mycorrhization of Vaccinium myrtillus roots was also observed. The latter findings establish the pivotal role of SOD1 as an important factor in the relationship between O. maius and its symbiotic partner. The lack of this ROS-scavenger may cause an imbalance in the redox homeostasis during host colonization and an alteration in the delicate dialogue between the fungus and its host plant.

Responses of Candida fukuyamaensis RCL-3 and Rhodotorula mucilaginosa RCL-11 to copper stress

The effect of high Cu(II) concentrations on superoxide dismutase (SOD) and catalase (CAT) activity in Candida fukuyamaensis RCL-3 and Rhodotorula mucilaginosa RCL-11, previously isolated from a copper filter at a mine plant in Argentina, was studied. Addition of 0.1, 0.2 and 0.5 mM Cu(II) to the culture medium increased total SOD and CAT activity in both strains. Native polyacrylamide gel electrophoresis revealed two bands with SOD activity for C. fukuyamaensis RCL-3 and only one for R. mucilaginosa RCL-11; the three bands corresponded to MnSOD.Intracellular accumulation of copper and morphological changes was observed using electron microscopy. Dark bodies examined with transmission electron microscopy (TEM) after 48 h of incubation probably corresponded to copper deposits. The number of dark bodies in R. mucilaginosa RCL-11 grew with increasing incubation time, whereas in C. fukuyamaensis RCL-3 the amount decreased. Scanning electron micrographs (SEM) of C. fukuyamaensis RCL-3 did not reveal any differences compared with the control, but R. mucilaginosa RCL-11 cells were bigger than control ones. TEM confirmed absence of compartmentalization mechanisms in Cu(II) detoxification since electron-dense bodies were mainly found in the cytoplasm.

Tolerance and stress response of Macrolepiota procera to nickel

Nickel (Ni) is an essential element for many organisms; however, it is very toxic at high concentrations and also depending on the species. In macrofungi the mechanisms underlying their Ni tolerance are poorly documented. This study examines, for the first time, the participation of the antioxidative system in Macrolepiota procera exposed to different Ni2+ concentrations and their relation with Ni tolerance. The effect of the pH on Ni tolerance was also evaluated. The fungus was cultivated on solid medium with different NiCl2 concentrations (0.05, 0.2, 0.8 mM) at pH 4, 6, and 8, and fungi growth and Ni uptake were determined. The antioxidative enzymes catalase (CAT) and superoxide dismutase (SOD) and the production of hydrogen peroxide H2O2 were evaluated on fungal submerged cultures within the first hours of Ni2+ exposure. Results showed that M. procera growth decreased when Ni2+ concentrations increased, reaching a maximum growth inhibition (>80%) up to 0.2 mM of NiCl2. Ni uptake increased proportionally to Ni increase in the medium. Both Ni tolerance and Ni accumulation were affected by medium pH. Microscope observations showed differences in the size of spores produced by fungi at different Ni concentrations. Ni exposure induced oxidative stress, as indicated by the production of H2O2, the levels of which seem to be regulated by the antioxidant enzymes SOD and CAT. The time variation pattern of SOD and CAT activities indicated that the former has a greater role in alleviating the stress. The results obtained suggested that tolerance of M. procera to Ni2+ is associated with the ability of this macrofungus to initiate an efficient antioxidant defense system.

Heavy metals generate reactive oxygen species in terrestrial and aquatic ciliated protozoa

Reactive oxygen species (ROS) induction by exposure to heavy metals (Cd, Cu or Zn) in diverse free-living ciliated protozoa (Tetrahymena sp. and three strains of Colpoda steinii, isolated from freshwater and soils with different level of metal pollution) has been evaluated. Using specific fluorophores, such as 2',7'-dichlorofluorescein diacetate, hydroethidine and dihydrorhodamine 123, and a fluorescence microscope with the program MetaMorph Imaging System 4.0, we have analyzed both the average fluorescence emission and the heterogeneous distribution of fluorescence in control and treated cells. This is the first time that these fluorophores are used to detect ROS production in ciliated protozoa. All metals generate ROS, mainly superoxide and peroxides, showing a remarkable inter- and intra-specific variations. Likewise, resistance against each metal was also very diverse. Cu and specially Cd, the most toxic heavy metal for these ciliates, are the best oxidative stress inducers. However, a correlation between fluorescence emission intensity and cellular metal sensitivity for each strain cannot be established. Results are discussed and compared with similar findings previously published in other unicellular and pluricellular organisms.

Cd (II) stress response during the growth of Aspergillus niger B 77

AIMS

To investigate the relationship between growth, heavy metal ions uptake and participation of the antioxidant enzymes superoxide dismutase (SOD) and catalase (CAT) in the protection of Aspergillus niger B 77 against cadmium stress.

METHODS AND RESULTS

The stress response of the model fungal strain, under conditions of a wide range of Cd (II) ion concentrations, was investigated by determining the biomass formation, protein biosynthesis, SOD and CAT activities and heavy metal uptake in growing cells. Exposure to heavy metal ions induced an increase in protein content, heavy metal uptake and SOD activity, and a heavy decrease in CAT activity.

CONCLUSION

The results obtained indicated that the tolerance of A. niger to Cd (II) was correlated with the heavy metal uptake, reactive oxygen species generation in the cells and the efficiency of antioxidative defence system.

SIGNIFICANCE AND IMPACT OF THE STUDY

Evidence is provided for the possibility that oxidative stress plays a major role in the effect of Cd (II) ions on A. niger. These data could offer useful information when creating new strategies and methodological improvements for bioremediation with the participation of fungi.

Cadmium-resistance in growing Rhodotorula sp. Y11

The uptake of cadmium and responses to this metal were studied in growing Rhodotorula sp. Y11. In presence of cadmium, Y11 showed a similar lag phase with decreased mu(max) in comparison to the control cultures in the absence of cadmium. Different changes in contents of cell elemental composition (carotenoids, total protein, total soluble sugar, and phosphate content) were observed under cadmium pressure. Growing Rhodotorula sp. Y11 took up cadmium in a biphasic mode, involving an initial energy-independent biosorption to the cell surface, followed by a slower energy-dependent intracellular accumulation. In the presence of metabolic inhibitors, intracellular cadmium uptake of growing Y11 was significantly influenced.

Responses in the mycelial growth of Aspergillus niger isolates to arsenic contaminated environments and their resistance to exogenic metal stress

Isolates of Aspergillus niger, selected from coal dust sediment of a mine containing As (400 mg/kg), pH 3.3-2.8, and from river sediment found near the mine (As, 363 mg/kg, Sb, 93 mg/kg), pH 5.2-4.8, growing on Czapek-Dox agar exhibited distinct responses in the mycelial growth in arsenic contaminated environments. The radial growth of the isolate from the coal dust in comparison to the control strain from an environment without pollution was reduced approximately to one-half. It formed black, very small compact colonies, with dense sporulation. The opposite, the strain from the river sediment, grew better in Czapek-Dox agar like the control. It formed larger colonies with dense centre and strong sporulation. Also, the culture from river sediment developed faster than the coal dust isolate and control strain. Differences were also recorded in size and thickness of conidia heads, phialide, metulae, and conidiophores. Both isolates from contaminated localities exhibited higher tolerance to exogenic toxic effects of As5+, Cd2+ and Cu2+ (5, 25 or 50 mg/l) than the control culture. Tolerance was monitored using the growth of biomass in liquid Czapek-Dox medium. We confirmed the morphological identification of our isolates to A. niger species with the PCR method. The results refer to complicated relations between biotic and abiotic effects that may directly affect the processes observed in the in situ environment.

Gene expression profiling of a Zn-tolerant and a Zn-sensitive Suillus luteus isolate exposed to increased external zinc concentrations

Complementary DNA (cDNA)-amplified fragment-length polymorphism (AFLP) was applied to analyze transcript profiles of a Zn-tolerant and a Zn-sensitive isolate of the ectomycorrhizal basidiomycete Suillus luteus, both cultured with and without increased external zinc concentrations. From the obtained transcript profiles that covered approximately 2% of the total expected complement of genes in S. luteus, 144 nonredundant, differentially expressed transcript-derived fragments (TDFs), falling in different classes of expression pattern, were isolated and sequenced. Thirty-six of the represented genes showed homology to function-known genes, whereas 6 matched unknown protein coding sequences, and 102 were possibly novel. Although relatively few TDFs were found to be responsive to the different zinc treatments, their modulated expression levels may suggest a different transcriptional response to zinc treatments in both isolates. Among the identified genes that could be related to heavy-metal detoxification or the tolerance trait were genes encoding for homologues of a heat-shock protein, a putative metal transporter, a hydrophobin, and several proteins involved in ubiquitin-dependent proteolysis.

Responses of antioxidant defenses to Cu and Zn stress in two aquatic fungi

Aquatic hyphomycetes are fungi that play a key role in plant litter decomposition in streams. Even though these fungi occur in metal-polluted streams, the mechanisms underlying their tolerance to metals are poorly documented. We addressed the effects of Zn and Cu in Varicosporium elodeae and Heliscus submersus by examining metal adsorption to cell walls, plasma membrane integrity and production of reactive oxygen species at metal concentrations inhibiting biomass production in 50% or 80%. The activity of the enzymes catalase, superoxide dismutase and glucose-6-phosphate dehydrogenase was measured to elucidate their role in coping with oxidative stress induced by metals at short- (14 h) and long- (8 days) term exposure. Results show that V. elodeae was more susceptible to the toxic effects induced by Cu and Zn than H. submersus, as indicated by more extensive inhibition of biomass production. Both metals, particularly Cu, induced oxidative stress in the two fungal species, as shown by the noticeable recovery of biomass production in the presence of an antioxidant agent. In both fungi, Cu induced a more severe disruption of plasma membrane integrity than Zn. Our studies on antioxidant defenses showed that catalase had a greater role alleviating stress induced by Zn and Cu than superoxide dismutase. Chronic metal stress also stimulated the production of NADPH, via the pentose phosphate pathway by increasing the activity of glucose-6-phosphate dehydrogenase. Our results suggest that the tolerance of aquatic hyphomycetes to Cu and Zn is associated with the ability of these fungi to initiate an efficient antioxidant defense system.

Gene expressions and enzyme analyses in the Schizosaccharomyces pombe Deltapap1 transcription factor mutant exposed to Cd(2+)

The objective of this study was to investigate the role of the Pap1 transcription factor in response to long-term Cd(2+) stress. The Schizosaccharomyces pombe wild-type strain and the Deltapap1 mutant, treated with 0.5 mM CdSO(4), were used in antioxidant enzyme and gene expression experiments. The Deltapap1 mutant proved to be sensitive to Cd(2+) in the spot test assay, suggesting that the Pap1 transcription factor plays an important role in the response to Cd(2+) stress. The Cd(2+) uptake was the same in both strains. Determination of the superoxide level in the wild-type strain proved that superoxide was generated, suggesting that long-term Cd(2+) treatment could trigger oxidative stress. Furthermore, the Deltapap1 mutant displayed higher amounts of superoxide. These results were supported by the significantly lower amount of peroxide generated in the reaction catalyzed by superoxide dismutase (SOD). The Deltapap1 mutant had a significantly lower glutathione S-transferase specific activity than that of the wild-type strain during long-term Cd(2+) stress, caused by the lower GSH and sulfide assimilation. We have demonstrated that GST III activity was not induced by Cd(2+) stress in the Deltapap1 mutant. The overall low GST activity was not sufficient for the cell to eliminate Cd(2+) caused damage and could result in a Cd(2+)-sensitive phenotype of the Deltapap1 mutant. The RT-PCR and Northern blot experiments proved that gst2 was not induced either by short-term or by long-term Cd(2+) treatment. The SPCC965.06 (a putative K(+) ion channel subunit) gene expression increased, while the hmt1 (an ABC-type vacuolar transporter protein) expression decreased in both strains. No detectable alteration in the mRNA levels of, gpx1, hmt2, sod1, sod, and trx1 was observed. SOD enzyme analyses revealed that the absence of Pap1 protein could result in a lower SODs activity and affect the sulfate assimilation. This is the first report on the fact that the Pap1 transcription factor could play an important role in the cellular post-transcriptional/post-translational enzyme activity induction processes of SODs that occur in response to Cd(2+).