Inhibition Of Yeast Growth Research Articles

In vitro Evaluation of Antifungal Activity of Terbinafine Nano Form against Yeast Organism Isolated in Thumby Labs Ajman

The goal of this study is to evaluate the antifungal activity of terbinafine in its nano form against yeast organisms in vitro and compare its effectiveness to the normal form of terbinafine. Thirty isolated yeast organisms from Thumbay Labs were included in the study. Terbinafine was serially diluted to concentrations of 50 mg, 25 mg, 12 mg, and 6 mg for both the nano and normal forms. After preparing the serial dilutions, fungal suspensions were exposed to these dilutions for 7 minutes. The suspensions were then cultured on Sabouraud dextrose agar and incubated at 37°C overnight. Growth was measured using a colony count. The results for the normal form of terbinafine revealed growth at all concentrations, with varying colony counts with a highest growth was observed at the 6 mg concentration. In contrast, the nano form of terbinafine exhibited distinct development patterns. At the 50 mg concentration, seven samples showed no growth; at the 25 mg concentration, two samples showed no growth; and the remaining samples exhibited limited growth compared to the normal form. According to the results of this study, there were significant differences in the number of colonies between the two forms of terbinafine, with the nano form demonstrating greater efficacy. The most potent antifungal response was observed at the 50 mg concentration of nano terbinafine, which inhibited yeast growth in several samples. In conclusion, terbinafine nanoemulsions are more effective than the normal form against Candida.

Identification and Preliminary Functional Analysis of Responsive Genes to Short-term Heat Stress in Lettuce

Lettuce is a commonly consumed vegetable worldwide, due to its crisp edible organs and rich nutrition. Heat stress is known to seriously threaten its growth and development. However, research on lettuce response to heat stress focusing on molecular aspects is limited. Therefore, we aimed to understand the complex molecular mechanisms underlying the regulation of lettuce plant response to heat stress (37 °C), by transcriptomic analysis of a heat-resistant lettuce variety (K482) following heat stress treatment for 1.5 and 3 days. A total of 3798 and 4121 differentially expressed genes (DEGs) were identified at 1.5 and 3 days vs. the control after heat treatment, respectively; they were mostly enriched in protein processing in the systemic lupus erythematosus, alcoholism, neurotrophin signaling pathways, and the cell cycle. Most DEGs were NACs, HSPs, MYBs, bHLHs, and WRKYs. Transcriptome analysis showed that the NAC domain transcription factor LsNAC28, which is associated with heat response, is up-regulated during heat stress and LsNAC28 inhibited yeast growth under heat stress (37 °C). These findings provide a basis to comprehensively understand the complex molecular mechanism of lettuce response to heat stress.

Sustainable succinic acid production from lignocellulosic hydrolysates by engineered strains of Yarrowia lipolytica at low pH

Succinic acid (SA) is a valuable C4 platform chemical with diverse applications. Lignocellulosic biomass represents an abundant and renewable carbon resource for microbial production of SA. However, the presence of toxic compounds in pretreated lignocellulosic hydrolysates poses challenges to cell metabolism, leading to inefficient SA production. Here, engineered Yarrowia lipolytica Hi-SA2 was shown to utilize glucose and xylose from corncob hydrolysate to produce 32.6 g/L SA in shaking flasks. The high concentration of undetoxified hydrolysates significantly inhibited yeast growth and SA biosynthesis, with furfural identified as the key inhibitor. Through overexpressing glutathione synthetase encoding gene YlGsh2, the tolerance of engineered strain to furfural and toxic hydrolysate was significantly improved. In a 5-L bioreactor, Hi-SA2-YlGsh2 strain produced 45.34 g/L SA within 32 h, with a final pH of 3.28. This study provides a sustainable process for bio-based SA production, highlighting the efficient SA synthesis from lignocellulosic biomass through low pH fermentation.

A random mutagenesis screen enriched for missense mutations in bacterial effector proteins.

To remodel their hosts and escape immune defenses, many pathogens rely on large arsenals of proteins (effectors) that are delivered to the host cell using dedicated translocation machinery. Effectors hold significant insight into the biology of both the pathogens that encode them and the host pathways that they manipulate. One of the most powerful systems biology tools for studying effectors is the model organism, Saccharomyces cerevisiae. For many pathogens, the heterologous expression of effectors in yeast is growth inhibitory at a frequency much higher than housekeeping genes, an observation ascribed to targeting conserved eukaryotic proteins. Abrogation of yeast growth inhibition has been used to identify bacterial suppressors of effector activity, host targets, and functional residues and domains within effector proteins. We present here a yeast-based method for enriching for informative, in-frame, missense mutations in a pool of random effector mutants. We benchmark this approach against three effectors from Legionella pneumophila, an intracellular bacterial pathogen that injects a staggering >330 effectors into the host cell. For each protein, we show how in silico protein modeling (AlphaFold2) and missense-directed mutagenesis can be combined to reveal important structural features within effectors. We identify known active site residues within the metalloprotease RavK, the putative active site in SdbB, and previously unidentified functional motifs within the C-terminal domain of SdbA. We show that this domain has structural similarity with glycosyltransferases and exhibits in vitro activity consistent with this predicted function.

Genetic evidence for a regulated cysteine protease catalytic triad in LegA7, a Legionella pneumophila protein that impinges on a stress response pathway.

Legionella pneumophila grows within membrane-bound vacuoles in phylogenetically diverse hosts. Intracellular growth requires the function of the Icm/Dot type-IVb secretion system, which translocates more than 300 proteins into host cells. A screen was performed to identify L. pneumophila proteins that stimulate MAPK activation, using Icm/Dot translocated proteins ectopically expressed in mammalian cells. In parallel, a second screen was performed to identify L. pneumophila proteins expressed in yeast that cause growth inhibition in MAPK pathway-stimulatory high osmolarity medium. LegA7 was shared in both screens, a protein predicted to be a member of the bacterial cysteine protease family that has five carboxyl-terminal ankyrin repeats. Three conserved residues in the predicted catalytic triad of LegA7 were mutated. These mutations abolished the ability of LegA7 to inhibit yeast growth. To identify other residues important for LegA7 function, a generalizable selection strategy in yeast was devised to isolate mutants that have lost function and no longer cause growth inhibition on high osmolarity medium. Mutations were isolated in the two carboxyl-terminal ankyrin repeats, as well as an inter-domain region located between the cysteine protease domain and the ankyrin repeats. These mutations were predicted by AlphaFold modeling to localize to the face opposite from the catalytic site, arguing that they interfere with the positive regulation of the catalytic activity. Based on our data, we present a model in which LegA7 harbors a cysteine protease domain with an inter-domain and two carboxyl-terminal ankyrin repeat regions that modulate the function of the catalytic domain.

Unravelling bacterial virulence factors in yeast: From identification to the elucidation of their mechanisms of action.

Pathogenic bacteria employ virulence factors (VF) to establish infection and cause disease in their host. Yeasts, Saccharomyces cerevisiae and Saccharomyces pombe, are useful model organisms to study the functions of bacterial VFs and their interaction with targeted cellular processes because yeast processes and organelle structures are highly conserved and similar to higher eukaryotes. In this review, we describe the principles and applications of the yeast model for the identification and functional characterisation of bacterial VFs to investigate bacterial pathogenesis. The growth inhibition phenotype caused by the heterologous expression of bacterial VFs in yeast is commonly used to identify candidate VFs. Then, subcellular localisation patterns of bacterial VFs can provide further clues about their target molecules and functions during infection. Yeast knockout and overexpression libraries are also used to investigate VF interactions with conserved eukaryotic cell structures (e.g., cytoskeleton and plasma membrane), and cellular processes (e.g., vesicle trafficking, signalling pathways, and programmed cell death). In addition, the yeast growth inhibition phenotype is also useful for screening new drug leads that target and inhibit bacterial VFs. This review provides an updated overview of new tools, principles and applications to study bacterial VFs in yeast.

Antifungal efficacy of natural antimicrobial substances during the fermentation and storage of hardaliye

Hardaliye is a non-alcoholic traditional fermented beverage produced using black grapes, mustard seeds, sour cherry leaves, and sodium benzoate. In this study, the effect of using plant materials (quince leaves, green tea, mulberry leaves, linden flowers, horseradish roots) as an alternative to sodium benzoate for inhibiting yeast growth to produce additive-free hardaliye was investigated. Hardaliye samples were produced using the selected test materials, microbiological and chemical analyses were performed during fermentation (20 °C for 18 days) and storage (4 °C for 2 months) periods. Additionally, the antifungal effects of test material extracts against Saccharomyces cerevisiae in grape juice and Malt Extract Broth (MEB), as well as the survival of S. cerevisiae in grape juice containing plant materials were examined. Only mustard seed extract had inhibitory and fungicidal effects at 25 mg/mL on S. cerevisiae in MEB among the tested plant material extracts and the effect increased when used in combination with grape juice. The total phenolic contents of the hardaliye samples were in the range of 2119.26–8653.33 mg gallic acid equivalents (GAE)/L, and antioxidant activities were in the range of 30.24–93.15%. The numbers of S. cerevisiae decreased below the detection limit (<1 log CFU/mL) after 1 day in grape juice containing horseradish (5%), mustard seeds (1.5%) or sodium benzoate (0.1%). This study indicated that crushed mustard seeds at increased concentrations (1.5%), mustard seeds water extract (7.5 mg/mL), or horseradish roots (5%) have the potential to be used in the production of hardaliye as an alternative to sodium benzoate.

Unveiling the molecular networks underlying cellular impairment in Saccharomyces cerevisiae: investigating the effects of magnesium oxide nanoparticles on cell wall integrity and endoplasmic reticulum stress response.

Nanoparticles, particularly magnesium oxide nanoparticles (MgO-NPs), are increasingly utilized in various fields, yet their potential impact on cellular systems remains a topic of concern. This study aimed to comprehensively investigate the molecular mechanisms underlying MgO-NP-induced cellular impairment in Saccharomyces cerevisiae, with a focus on cell wall integrity, endoplasmic reticulum (ER) stress response, mitochondrial function, lipid metabolism, autophagy, and epigenetic alterations. MgO-NPs were synthesized through a chemical reduction method, characterized for morphology, size distribution, and elemental composition. Concentration-dependent toxicity assays were conducted to evaluate the inhibitory effect on yeast growth, accompanied by propidium iodide (PI) staining to assess membrane damage. Intracellular reactive oxygen species (ROS) accumulation was measured, and chitin synthesis, indicative of cell wall perturbation, was examined along with the expression of chitin synthesis genes. Mitochondrial function was assessed through Psd1 localization, and ER structure was analyzed using dsRed-HDEL marker. The unfolded protein response (UPR) pathway activation was monitored, and lipid droplet formation and autophagy induction were investigated. Results demonstrated a dose-dependent inhibition of yeast growth by MgO-NPs, with concomitant membrane damage and ROS accumulation. Cell wall perturbation was evidenced by increased chitin synthesis and upregulation of chitin synthesis genes. MgO-NPs impaired mitochondrial function, disrupted ER structure, and activated the UPR pathway. Lipid droplet formation and autophagy were induced, indicating cellular stress responses. Additionally, MgO-NPs exhibited differential cytotoxicity on histone mutant strains, implicating specific histone residues in cellular response to nanoparticle stress. Immunoblotting revealed alterations in histone posttranslational modifications, particularly enhanced methylation of H3K4me. This study provides comprehensive insights into the multifaceted effects of MgO-NPs on S. cerevisiae, elucidating key molecular pathways involved in nanoparticle-induced cellular impairment. Understanding these mechanisms is crucial for assessing nanoparticle toxicity and developing strategies for safer nanoparticle applications.

FlgI Is a Sec-Dependent Effector of Candidatus Liberibacter asiaticus That Can Be Blocked by Small Molecules Identified Using a Yeast Screen.

Huanglongbing (HLB) is one of the most devastating diseases of citrus worldwide. The phloem-restricted bacterium Candidatus Liberibacter asiaticus (CLas) is considered to be the main pathogen responsible for HLB. There is currently no effective practical strategy for the control of HLB. Our understanding of how pathogens cause HLB is limited because CLas has not been artificially cultured. In this study, 15 potential virulence factors were predicted from the proteome of CLas through DeepVF and PHI-base searches. One among them, FlgI, was found to inhibit yeast growth when expressed in Saccharomyces cerevisiae. The expression of the signal peptide of FlgI fused with PhoA in Escherichia coli resulted in the discovery that FlgI was a novel Sec-dependent secretory protein. We further found that the carboxyl-terminal HA-tagged FlgI was secreted via outer membrane vesicles in Sinorhizobium meliloti. Fluoresence localization of transient expression FlgI-GFP in Nicotiana benthamiana revealed that FlgI is mainly localized in the cytoplasm, cell periphery, and nuclear periphery of tobacco cells. In addition, our experimental results suggest that FlgI has a strong ability to induce callose deposition and cell necrosis in N. benthamiana. Finally, by screening a large library of compounds in a high-throughput format, we found that cyclosporin A restored the growth of FlgI-expressing yeast. These results confirm that FlgI is a novel Sec-dependent effector, enriching our understanding of CLas pathogenicity and helping to develop new and more effective strategies to manage HLB.

Transcriptional response of Saccharomyces cerevisiae to lactic acid enantiomers

The model yeast, Saccharomyces cerevisiae, is a popular object for both fundamental and applied research, including the development of biosensors and industrial production of pharmaceutical compounds. However, despite multiple studies exploring S. cerevisiae transcriptional response to various substances, this response is unknown for some substances produced in yeast, such as D-lactic acid (DLA). Here, we explore the transcriptional response of the BY4742 strain to a wide range of DLA concentrations (from 0.05 to 45 mM), and compare it to the response to 45 mM L-lactic acid (LLA). We recorded a response to 5 and 45 mM DLA (125 and 113 differentially expressed genes (DEGs), respectively; > 50% shared) and a less pronounced response to 45 mM LLA (63 DEGs; > 30% shared with at least one DLA treatment). Our data did not reveal natural yeast promoters quantitatively sensing DLA but provide the first description of the transcriptome-wide response to DLA and enrich our understanding of the LLA response. Some DLA-activated genes were indeed related to lactate metabolism, as well as iron uptake and cell wall structure. Additional analyses showed that at least some of these genes were activated only by acidic form of DLA but not its salt, revealing the role of pH. The list of LLA-responsive genes was similar to those published previously and also included iron uptake and cell wall genes, as well as genes responding to other weak acids. These data might be instrumental for optimization of lactate production in yeast and yeast co-cultivation with lactic acid bacteria.Key points• We present the first dataset on yeast transcriptional response to DLA.• Differential gene expression was correlated with yeast growth inhibition.• The transcriptome response to DLA was richer in comparison to LLA.

Computer-made peptide RQ18 acts as a dual antifungal and antibiofilm peptide though membrane-associated mechanisms of action

The spread of fungi resistant to conventional drugs has become a threatening problem. In this context, antimicrobial peptides (AMPs) have been considered as one of the main alternatives for controlling fungal infections. Here, we report the antifungal and antibiofilm activity and some clues about peptide RQ18's mechanism of action against Candida and Cryptococcus. This peptide inhibited yeast growth from 2.5 μM and killed all Candida tropicalis cells within 2 h incubation. Moreover, it showed a synergistic effect with antifungal agent the amphotericin b. RQ18 reduced biofilm formation and promoted C. tropicalis mature biofilms eradication. RQ18's mechanism of action involves fungal cell membrane damage, which was confirmed by the results of RQ18 in the presence of free ergosterol in the medium and fluorescence microscopy by Sytox green. No toxic effects were observed in murine macrophage cell lines and Galleria mellonella larvae, suggesting fungal target selectivity. Therefore, peptide RQ18 represents a promising strategy as a dual antifungal and antibiofilm agent that contributes to infection control without damaging mammalian cells.

Pluronic F-127 Enhances the Antifungal Activity of Fluconazole against Resistant Candida Strains.

Candida strains as the most frequent causes of infections, along with their increased drug resistance, pose significant clinical and financial challenges to the healthcare system. Some polymeric excipients were reported to interfere with the multidrug resistance mechanism. Bearing in mind that there are a limited number of marketed products with fluconazole (FLU) for the topical route of administration, Pluronic F-127 (PLX)/FLU formulations were investigated in this work. The aims of this study were to investigate (i) whether PLX-based formulations can increase the susceptibility of resistant Candida strains to FLU, (ii) whether there is a correlation between block polymer concentration and the antifungal efficacy of the FLU-loaded PLX formulations, and (iii) what the potential mode of action of PLX assisting FLU is. The yeast growth inhibition upon incubation with PLX formulations loaded with FLU was statistically significant. The highest efficacy of the azole agent was observed in the presence of 5.0 and 10.0% w/v of PLX. The upregulation of the CDR1/CDR2 genes was detected in the investigated Candida strains, indicating that the efflux of the drug from the fungal cell was the main mechanism of the resistance.

Pyrrole-Based Enaminones as Building Blocks for the Synthesis of Indolizines and Pyrrolo[1,2-a]pyrazines Showing Potent Antifungal Activity.

As a new approach, pyrrolo[1,2-a]pyrazines were synthesized through the cyclization of 2-formylpyrrole-based enaminones in the presence of ammonium acetate. The enaminones were prepared with a straightforward method, reacting the corresponding alkyl 2-(2-formyl-1H-pyrrol-1-yl)acetates, 2-(2-formyl-1H-pyrrol-1-yl)acetonitrile, and 2-(2-formyl-1H-pyrrol-1-yl)acetophenones with DMFDMA. Analogous enaminones elaborated from alkyl (E)-3-(1H-pyrrol-2-yl)acrylates were treated with a Lewis acid to afford indolizines. The antifungal activity of the series of substituted pyrroles, pyrrole-based enaminones, pyrrolo[1,2-a]pyrazines, and indolizines was evaluated on six Candida spp., including two multidrug-resistant ones. Compared to the reference drugs, most test compounds produced a more robust antifungal effect. Docking analysis suggests that the inhibition of yeast growth was probably mediated by the interaction of the compounds with the catalytic site of HMGR of the Candida species.

Cottonseed cake as nutritional additive for sorghum silages

ABSTRACT This study aimed to determine the optimal proportion of cottonseed cake (CSC) as an additive in sorghum silage to improve its chemical composition, fermentative profile, microbial populations, losses, dry matter recovery, and aerobic stability. Five treatments were evaluated, varying the inclusion of CSC at ensiling (0, 50, 100, 200, and 200 g kg−1 on fresh matter basis). The results showed that the inclusion of CSC significantly increased the content of dry matter, crude protein, and ether extract in the silages. Water-soluble carbohydrates, buffering capacity, and ammoniacal nitrogen exhibited a linear decrease with increasing CSC inclusion. The populations of lactic acid bacteria and moulds showed a quadratic response to CSC inclusion. The yeast population was completely inhibited with a minimum inclusion of 200 g kg−1 CSC. Aerobic stability and dry matter recovery showed a linear increase with CSC inclusion. These findings indicate that adding CSC to sorghum silage enhances its nutritive value, fermentative profile, dry matter recovery, and effectively inhibits yeast growth, which is recommended to include 200 g kg−1 of CSC for good cost-effectiveness.

Crystal structure of dihydrofolate reductase from the emerging pathogenic fungus Candida auris.

Candida auris has emerged as a global health problem with a dramatic spread by nosocomial transmission and a high mortality rate. Antifungal therapy for C.auris infections is currently limited due to widespread resistance to fluconazole and amphotericin B and increasing resistance to the front-line drug echinocandin. Therefore, new treatments are urgently required to combat this pathogen. Dihydrofolate reductase (DHFR) has been validated as a potential drug target for Candida species, although no structure of the C. auris enzyme (CauDHFR) has been reported. Here, crystal structures of CauDHFR are reported as an apoenzyme, as a holoenzyme and in two ternary complexes with pyrimethamine and cycloguanil, which are common antifolates, at near-atomic resolution. Preliminary biochemical and biophysical assays and antifungal susceptibility testing with a variety of classical antifolates were also performed, highlighting the enzyme-inhibition rates and the inhibition of yeast growth. These structural and functional data might provide the basis for a novel drug-discovery campaign against this global threat.

Human gasdermin D and MLKL disrupt mitochondria, endocytic traffic and TORC1 signalling in budding yeast.

Gasdermin D (GSDMD) and mixed lineage kinase domain-like protein (MLKL) are the pore-forming effectors of pyroptosis and necroptosis, respectively, with the capacity to disturb plasma membrane selective permeability and induce regulated cell death. The budding yeast Saccharomyces cerevisiae has long been used as a simple eukaryotic model for the study of proteins associated with human diseases by heterologous expression. In this work, we expressed in yeast both GSDMD and its N-terminal domain (GSDMD(NT)) to characterize their cellular effects and compare them to those of MLKL. GSDMD(NT) and MLKL inhibited yeast growth, formed cytoplasmic aggregates and fragmented mitochondria. Loss-of-function point mutants of GSDMD(NT) showed affinity for this organelle. Besides, GSDMD(NT) and MLKL caused an irreversible cell cycle arrest through TORC1 inhibition and disrupted endosomal and autophagic vesicular traffic. Our results provide a basis for a humanized yeast platform to study GSDMD and MLKL, a useful tool for structure-function assays and drug discovery.

The effect of growth inhibiting compounds of grease trap waste on Candida tropicalis ATCC 20962

The production of chemicals through a circular economy is becoming increasingly important and one way to achieve this is through the utilisation of waste streams. One such waste stream that holds potential for production of chemicals through biochemical methods is grease trap waste (GTW). However, before this waste stream can be used in bioprocesses, it is crucial to understand its effects on the process. This study explores the toxicity of the GTW on the growth of Candida tropicalis ATCC 20962, a yeast that is applied to convert lipids into valuable long-chain dicarboxylic acids (LCDAs). The GTW is characterised and the inhibition of the different components on the growth of C. tropicalis is examined. Results indicate significant inhibition of yeast growth at a concentration of 40 g/L of GTW and higher. Further analysis confirms that the presence of anionic detergents may partially contribute to this inhibition. In contrast, the pesticides, free fatty acids and heavy metals did not appear to significantly affect the growth of C. tropicalis. Although this study suggests that GTW could be a suitable feedstock for Candida tropicalis ATCC 20962, more research is required to identify other potentially toxic components and to determine if pre-treatment is necessary for industrial applications.

Physicochemical, antioxidant and microbial properties of sweetened yoghurt produced from partial substitution of sugar with soursop puree

This study was targeted towards evaluating the outcome of partially substituting sugar with soursop puree at different proportions, varying pasteurization temperatures, storage durations and with the application of sodium benzoate and potassium sorbate as chemical preservatives on physiochemical, antioxidant and microbial qualities of yoghurt. There was a strong correlation (R2 = 0.7, Adjusted R2 = 0.65) between the syneresis and the water-holding capacity of the yoghurt as the substitution increased. At 50% soursop puree substitution in the yoghurt production, DPPH radical scavenging activity, total phenolic content, vitamin C, carbohydrate, protein, and ash contents increased to 34.40%, 1.25 mg GAE/L, 58.50 mg/100 g, 29.26, 4.02 and 0.69%, respectively. Storage duration does not have a significant influence on the proximate composition of the yoghurt samples. However, the vitamin C content of the yoghurt decreased when the pasteurization temperature was more than 80 °C. The growth of lactic acid bacteria ranged between 2.9 × 105 and 2.16 × 106 CFU/ml. The use of sodium benzoate inhibited yeast growth more than potassium sorbate while soursop substitution inhibited the growth of mould from 1.0 × 106 CFU/ml to 3.05 × 105 CFU/ml than the preservatives. Coliform was absent in all the yoghurt samples with or without preservatives. This information would be valuable in yoghurt development and quality control.Graphical

Antifungal and antiparasitic activity of Wunderlichia azulensis (Asteraceae) roots

The aim of this work was to evaluate the antifungal and antiparasitic activity of roots of Wunderlichia azulensis (Asteraceae). A CH2Cl2 partition of W. azulensis was tested against Candida tropicalis, C. buinensis and Trypanosoma cruzi parasites. A chemical study of the CH2Cl2 partition resulted in the isolation and identification of dehydrobrachylaenolide (1), lasiodiplodin (2), a taraxerane-type triterpene (3) and a mixture of sitosterol and stigmasterol (4–5). Of the 13 fractions tested, fractions 5 and 7 were the most bioactive ones. No live epimastigotes were observed even after the shortest time of exposure to fraction 7 (25 μg.mL−1/24 h). Fractions 5 and 7 inhibited yeast growth in proportions between 63.9–80.7% at 50 μg.mL−1, and 70.3–96.7% at 100 μg.mL−1. Fractions 5 and 7 (100 μg.mL−1) induced loss of viability of C. buinensis by 97.61 and 92.63%, respectively, whereas C. tropicalis was less susceptible. The SYTOX Green marker used on Candida yeasts suggested membrane permeabilization and consequently plasma membrane damage. We concluded that W. azulensis offers new sources of biologically-active components. However, complementary studies on other variables, such as synergy, toxicology, and mechanism of action, must be carried out.

Capsaicin toxicity to the yeast Saccharomyces cerevisiae is not due to oxidative stress but to disruption of membrane structure

Capsaicin (CAP) is a common food constituent, conferring a pungent taste to red peppers of the genus Capsicum. It has bactericidal and fungicidal activity. The study was aimed to test the hypothesis of whether oxidative stress mediates the toxicity of CAP to the baker's yeast Saccharomyces cerevisiae as a model yeast. CAP showed good antioxidant properties (1.30 and 1.10 mol Trolox equivalents/mol in the 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonate (ABTS) radical scavenging assay and the Ferric Reducing Antioxidant Power assay, respectively). However, its autoxidation generated hydrogen peroxide. CAP inhibited the growth of S. cerevisiae at concentrations ≥100 μM. Yeast mutants deficient in superoxide dismutase 1 or catalase T were more sensitive to CAP than wild-type yeast. CAP did not augment the ROS level in yeast cells. Standard antioxidants (N-acetylcysteine and ascorbate) did not protect significantly against CAP-induced yeast growth inhibition. Thus, oxidative stress does not mediate the CAP's inhibition of yeast growth. CAP did not decrease mitochondrial membrane potential of the yeast but induced a concentration-dependent decrease in membrane fluidity. These results indicate that the disturbance of membrane properties is the apparent cause of CAP toxicity to the yeast.