New Insights in Phenothiazinium-Mediated Photodynamic Inactivation of Candida Auris

In recent years, Candida auris has emerged as a hazardous hospital-acquired pathogen. Its resistance to antifungal treatments makes it challenging, requiring new approaches to manage it effectively. Herein, we aimed to assess the impact of photodynamic inactivation mediated by methylene blue (MB-PDI) or 1,9-dimethyl MB (DMMB-PDI) combined with a red LED against C. auris. To evaluate the photoinactivation of yeasts, we quantified colony-forming units and monitored ROS production. To gain some insights into the differences between MB and DMMB, we assessed lipid peroxidation (LPO) and mitochondrial membrane potential (ΔΨm). After, we verified the effectiveness of DMMB against biofilms by measuring metabolic activity and biomass, and the structures were analyzed through scanning electron microscopy and optical coherence tomography. We also evaluated the cytotoxicity in mammalian cells. DMMB-PDI successfully eradicated C. auris yeasts at 3 μM regardless of the light dose. In contrast, MB (100 μM) killed cells only when exposed to the highest dose of light. DMMB-PDI promoted higher ROS, LPO and ΔΨm levels than those of MB. Furthermore, DMMB-PDI was able to inhibit biofilm formation and destroy mature biofilms, with no observed toxicity in fibroblasts. We conclude that DMMB-PDI holds great potential to combat the global threat posed by C. auris.

A contrast of Pb(II), Cd(II), and Cu(II) toxicities to Aspergillus niger through biochemical, morphological, and genetic investigations

The toxicity of metals to microorganisms is highly correlated with the type of metal used. However, the differences in the resistance mechanisms of filamentous fungi to multiple metals remain unclear. In this study, we investigated the responses of Aspergillus niger to three toxic metals, i.e., Pb²⁺, Cd²⁺, and Cu²⁺. Fungal growth and metabolism indices showed that A. niger had a higher tolerance to Pb²⁺ (>1000 mg L^-1) than to Cu²⁺ (300 mg L^-1) and Cd²⁺ (50 mg L^-1). An appropriate Pb²⁺ concentration (<500 mg L^-1) stimulated fungal growth and metabolic activity, whereas Cd²⁺ and Cu²⁺ stress showed continuously negative influences on fungal physiological parameters, such as biomass and secretion of oxalic acid. A. niger responded to Pb stress by constructing a new border layer around its cell wall. This pathway was also confirmed using RNA-seq analysis, i.e., the gene encoding cell wall α-1,3-glucan synthase was upregulated. This upregulation subsequently promoted the production of polysaccharides, which are the main components that support fungal cell walls. In contrast, the expression of genes encoding both AAA family ATPase and efflux pump antibiotic resistance proteins for Cd²⁺ and Cu²⁺ was significantly downregulated. Therefore, these findings elucidated the relatively complete fungal responses to different metal stresses.

No Chance to Survive: Mo-CBP3-PepII Synthetic Peptide Acts on Cryptococcus neoformans by Multiple Mechanisms of Action

Multidrug-resistant Cryptococcus neoformans is an encapsulated yeast causing a high mortality rate in immunocompromised patients. Recently, the synthetic peptide Mo-CBP₃-PepII emerged as a potent anticryptococcal molecule with an MIC₅₀ at low concentration. Here, the mechanisms of action of Mo-CBP₃-PepII were deeply analyzed to provide new information about how it led C. neoformans cells to death. Light and fluorescence microscopies, analysis of enzymatic activities, and proteomic analysis were employed to understand the effect of Mo-CBP₃-PepII on C. neoformans cells. Light and fluorescence microscopies revealed Mo-CBP₃-PepII induced the accumulation of anion superoxide and hydrogen peroxide in C. neoformans cells, in addition to a reduction in the activity of superoxide dismutase (SOD), ascorbate peroxidase (APX), and catalase (CAT) in the cells treated with Mo-CBP₃-PepII. In the presence of ascorbic acid (AsA), no reactive oxygen species (ROS) were detected, and Mo-CBP₃-PepII lost the inhibitory activity against C. neoformans. However, Mo-CBP₃-PepII inhibited the activity of lactate dehydrogenase (LDH) ergosterol biosynthesis and induced the decoupling of cytochrome c (Cyt c) from the mitochondrial membrane. Proteomic analysis revealed a reduction in the abundance of proteins related to energetic metabolism, DNA and RNA metabolism, pathogenicity, protein metabolism, cytoskeleton, and cell wall organization and division. Our findings indicated that Mo-CBP₃-PepII might have multiple mechanisms of action against C. neoformans cells, mitigating the development of resistance and thus being a potent molecule to be employed in the production of new drugs against C. neoformans infections.

The Anti-Fungal Activity of Nitropropenyl Benzodioxole (NPBD), a Redox-Thiol Oxidant and Tyrosine Phosphatase Inhibitor

Phylogenetically diverse fungal species are an increasing cause of severe disease and mortality. Identification of new targets and development of new fungicidal drugs are required to augment the effectiveness of current chemotherapy and counter increasing resistance in pathogens. Nitroalkenyl benzene derivatives are thiol oxidants and inhibitors of cysteine-based molecules, which show broad biological activity against microorganisms. Nitropropenyl benzodioxole (NPBD), one of the most active antimicrobial derivatives, shows high activity in MIC assays for phylogenetically diverse saprophytic, commensal and parasitic fungi. NPBD was fungicidal to all species except the dermatophytic fungi, with an activity profile comparable to that of Amphotericin B and Miconazole. NPBD showed differing patterns of dynamic kill rates under different growth conditions for Candida albicans and Aspergillus fumigatus and was rapidly fungicidal for non-replicating vegetative forms and microconidia. It did not induce resistant or drug tolerant strains in major pathogens on long term exposure. A literature review highlights the complexity and interactivity of fungal tyrosine phosphate and redox signaling pathways, their differing metabolic effects in fungal species and identifies some targets for inhibition. A comparison of the metabolic activities of Amphotericin B, Miconazole and NPBD highlights the multiple cellular functions of these agents and the complementarity of many mechanisms. The activity profile of NPBD illustrates the functional diversity of fungal tyrosine phosphatases and thiol-based redox active molecules and contributes to the validation of tyrosine phosphatases and redox thiol molecules as related and complementary selective targets for antimicrobial drug development. NPBD is a selective antifungal agent with low oral toxicity which would be suitable for local treatment of skin and mucosal infections.

Influence of Heat Stress on Intestinal Epithelial Barrier Function, Tight Junction Protein, and Immune and Reproductive Physiology

The potential threat of global warming in the 21^st century is on the ecosystem through many aspects, including the negative impact of rising global temperature on the health of humans and animals, especially domestic animals. The damage caused by heat stress to animals has been more and more significant as the worldwide climate continues to rise, along with the breeding industry's expanding scale and stocking density, and it has become the most important stress-causing factor in southern China. In this review, we described the effects of heat stress on animal immune organs and immune system. The much-debated topic is how hyperthermia affects the tight junction barrier. Heat stress also induces inflammation in the body of animals causing low body weight and loss of appetite. This review also discussed that heat stress leads to hepatic disorder, and it also damages the intestine. The small intestine experiences ischemia, and the permeability of the intestine increases. Furthermore, the oxidative stress and mitogen-activated protein kinase (MAPK) pathways have a significant role in stress-induced cellular and organ injury. The study has shown that MAPK activity in the small intestine was increased by heat stress. Heat stress caused extreme small intestine damage, enhanced oxidative stress, and activated MAPK signaling pathways.

Broad-spectrum chemicals block ROS detoxification to prevent plant fungal invasion

Plant diseases cause a huge impact on food security and are of global concern. While application of agrochemicals is a common approach in the control of plant diseases currently, growing drug resistance and the impact of off-target effects of these compounds pose major challenges. The identification of pathogenicity-related virulence mechanisms and development of new chemicals that target these processes are urgently needed. One such virulence mechanism is the detoxification of reactive oxygen species (ROS) generated by host plants upon attack by pathogens. The machinery of ROS detoxification might therefore serve as a drug target for preventing plant diseases, but few anti-ROS-scavenging drugs have been developed. Here, we show that in the model system Botrytis cinerea secretion of the cytochrome c-peroxidase, BcCcp1 removes plant-produced H₂O₂ and promotes pathogen invasion. The peroxidase secretion is modulated by a Tom1-like protein, BcTol1, through physical interaction. We show that BcTol1 is regulated at different levels to enhance the secretion of BcCcp1 during the early infection stage. Inactivation of either BcTol1 or BcCcp1 leads to dramatically reduced virulence of B. cinerea. We identify two BcTol1-targeting small molecules that not only prevent B. cinerea invasion but also have effective activity against a wide range of plant fungal pathogens without detectable effect on the hosts. These findings reveal a conserved mechanism of ROS detoxification in fungi and provide a class of potential fungicides to control diverse plant diseases. The approach described here has wide implications for further drug discovery in related fields.

Oxidative stress response pathways in fungi

Fungal response to any stress is intricate, specific, and multilayered, though it employs only a few evolutionarily conserved regulators. This comes with the assumption that one regulator operates more than one stress-specific response. Although the assumption holds true, the current understanding of molecular mechanisms that drive response specificity and adequacy remains rudimentary. Deciphering the response of fungi to oxidative stress may help fill those knowledge gaps since it is one of the most encountered stress types in any kind of fungal niche. Data have been accumulating on the roles of the HOG pathway and Yap1- and Skn7-related pathways in mounting distinct and robust responses in fungi upon exposure to oxidative stress. Herein, we review recent and most relevant studies reporting the contribution of each of these pathways in response to oxidative stress in pathogenic and opportunistic fungi after giving a paralleled overview in two divergent models, the budding and fission yeasts. With the concept of stress-specific response and the importance of reactive oxygen species in fungal development, we first present a preface on the expanding domain of redox biology and oxidative stress.

Changes in Brassica oleracea Leaves Infected With Xanthomonas campestris pv. campestris by Proteomics Analysis

Understanding plant's response mechanisms against pathogenesis is fundamental for the development of resistant crop varieties and more productive agriculture. In this regard, "omic" approaches are heralded as valuable technologies. In this work, combining isobaric tags for relative and absolute quantification (iTRAQ) technology with mass spectrometry, the proteomes from leaves of Brassica oleracea plants infected with Xanthomonas campestris pv. campestris (Xcc), and control plants at two different post-infection times were compared. Stronger proteomic changes were obtained at 12 days post-infection in comparison with 3 days. The responses observed involved different cell processes, from primary metabolism, such as photosynthesis or photorespiration, to other complex processes such as redox homeostasis, hormone signaling, or defense mechanisms. Most of the proteins decreased in the earlier response were involved in energetic metabolism, whereas later response was characterized by a recovery of primary metabolism. Furthermore, our results indicated that proteolysis machinery and reactive oxygen species (ROS) homeostasis could be key processes during this plant-pathogen interaction. Current data provide new insights into molecular mechanisms that may be involved in defense responses of B. oleracea to Xcc.

Functional properties of Rhizopus oryzae strains isolated from agricultural soils as a potential probiotic for broiler feed fermentation

The most crucial and expensive fragment in the broiler chicken production industry is the feed. Because of the rising demand, finding a cheap and effective feed is an urgent necessity. Fermentation of broiler feed by probiotic fungal starters can enhance the nutrient's availability and digestibility while preventing pathogenic growth. In this study different Rhizopus spp. have been isolated from agricultural soils around Izmir, Turkey, and tested for their probiotic potential and fermentative capacity. The isolated Rhizopus strains first underwent microscopical fluorescent investigation to exclude endofungal bacterial presence, then, those without endofungal bacteria (totally 82) were tested for antimicrobial activity counter bacterial and fungal pathogens. The ones with wide-spectrum antimicrobial activity (totally 10) were tested for gastrointestinal tolerance and antioxidant ability. Upon phenotypic and genotypic identification, the 10 isolates were found to belong to Rhizopus oryzae species. While all 10 strains showed variable gastrointestinal tolerance and antioxidant activities, three of them (92/1, 236/2, and 284) had relatively high antioxidant activity. Upon fermentative capacity assay, compared to unfermented commercial feed, there was a general decrease in crude fiber content by 56% after fermentation by 92/1 isolate for 4 days and 236/2 isolate for 2 days. The highest increase in crude protein content (by 14.5%) occurred after a 4-day fermentation period by 236/2 isolate. The highest increase in metabolizable energy was 8.64%, by the 284 isolate after 2 days of fermentation. In conclusion, the three strains showed good probiotic properties and fermentative capacities hence can be beneficial for the poultry industry.

Antioxidant and Antiradical Properties of Probiotic Strains Bacillus amyloliquefaciens ssp. plantarum

The aim of the present study was to investigate the in vitro antioxidant potential of the cell-free extracts (CFE) of two probiotic bacteria Bacillus amyloliquefaciens ssp. plantarum IMV B-7142 and Bacillus amyloliquefaciens ssp. plantarum IMV B-7143 and their hepatoprotective effects. These strains are the main components of the veterinary probiotic preparation endosporyn. The CFE of probiotic bacteria were able to stabilize the 2.2-diphenyl-1-picrylhydrazyl radical to its neutral form at their cultivation during 24-48 h. But this index was more pronounced for the IMV B-7142 strain and amounted to 44.4-51.2%. The hydroxyl radical scavenging activity of the CFE of probiotic bacteria increased more than 70-80% regardless of the cultivation period (24-48 h). The antioxidant potential of probiotic strains is associated with the synthesis of the multiple biologically active molecules. The phenolic and benzoic acids-antioxidants (gallic, 4-hydroxyphenylacetic, caffeic, syringic, p-coumaric, trans-ferulic, and trans-cinnamic acids) were identified among metabolites of B. amyloliquefaciens ssp. plantarum strains. The CFE of probiotic strains were able to protect of rat hepatocytes from the toxic effects of the carbon tetrachloride (CCl₄). Post-treatment of stress-induced rat hepatocytes by CFE of the IMV B-7042 was accompanied by an increase of the catalase activity of cells by 485.2 mM/min × mg of protein, compared to stress-damaged sample. In doing so, the content of the main markers of oxidative stress: lipid hydroperoxides and malondialdehyde decreased significantly. The results suggested that CFE of both probiotic strains have potent antioxidant properties and effectively protect of stress-damaged rat hepatocytes.

The Glycosylphosphatidylinositol-Anchored Superoxide Dismutase of Scedosporium apiospermum Protects the Conidia from Oxidative Stress

Scedosporium species are common fungal pathogens in patients with cystic fibrosis (CF). To colonize the CF lungs, fungi must cope with the host immune response, especially the reactive oxygen species (ROS) released by phagocytic cells. To this aim, pathogens have developed various antioxidant systems, including superoxide dismutases (SODs) which constitute the first-line protection against oxidative stress. Interestingly, one of the S. apiospermum SOD-encoding genes (SODD gene) exhibits a glycosylphosphatidylinositol (GPI) anchor-binding site and encodes a conidial-specific surface SOD. In this study, a SODDΔ mutant was engineered from a non-homologous end joining-deficient strain (KU70Δ) of S. apiospermum. Compared to its parent strain, the double mutant KU70Δ/SODDΔ exhibited increased susceptibility to various oxidizing agents and triazole antifungals. In addition, the loss of SodD resulted in an increased intracellular killing of the conidia by M1 macrophages derived from human blood monocytes, suggesting the involvement of this superoxide dismutase in the evasion to the host defenses. Nevertheless, one cannot disregard an indirect role of the enzyme in the synthesis or assembly of the cell wall components since transmission electron microscopic analysis revealed a thickening of the inner cell wall layer of the conidia. Further studies are needed to confirm the role of this enzyme in the pathogenesis of Scedosporium infections, including the production of a recombinant protein and study of its protective effect against the infection in a mouse model of scedosporiosis.

Studying the Ability of Thymol to Improve Fungicidal Effects of Tebuconazole and Difenoconazole Against Some Plant Pathogenic Fungi in Seed or Foliar Treatments

Thymol, a secondary plant metabolite possessing antifungal and chemosensitizing activities, disrupts cell wall or membrane integrity and interferes with ergosterol biosynthesis. Thymol also functions as a redox-active compound inducing generation of reactive oxygen species and lipid peroxidation in fungal cells. Previously, we showed thymol significantly enhanced the in vitro growth inhibitory effect of difenoconazole against Bipolaris sorokiniana and Parastagonospora nodorum. More recently, we demonstrated a possibility to use thymol to overcome the resistance of a P. nodorum strain able to grow on difenoconazole-containing media. However, potential for thymol to serve as a chemosensitizing agent in seed or plant treatments, to provide an effective suppression of the above-mentioned plant pathogens by triazole fungicides applied in lowered dosages, had yet to be tested. In the work presented here, we showed combined treatments of naturally infected barley seeds with thymol and difenoconazole (Dividend® 030 FS) synergistically exacerbated the protective effect against common root rot agent, B. sorokiniana, and other fungi (Fusarium spp. and Alternaria spp.). Similarly, co-applied treatment of wheat seeds, artificially inoculated with Fusarium culmorum, resulted in equivalent reduction of disease incidence on barley seedlings as application of Dividend®, alone, at a ten-fold higher dosage. In foliar treatments of wheat seedlings, thymol combined with Folicur® 250 EC (a.i. tebuconazole) enhanced sensitivity of P. nodorum, a glume/leaf blotch pathogen, to the fungicide and provided a significant mitigation of disease severity on treated seedlings, compared to controls, without increasing Folicur® dosages. Folicur® co-applied with thymol was also significantly more effective against a strain of P. nodorum tolerant to Folicur® alone. No additional deoxynivalenol or zearalenone production was found when a toxigenic F. culmorum was cultured in a nutrient medium containing thymol at a concentration used for chemosensitization of root rot agents. Accordingly, F. culmorum exposure to thymol at the sensitizing concentration did not up-regulate key genes associated with the biosynthesis of trichothecene or polyketide mycotoxins in this pathogen. Further studies using field trials are necessary to determine if thymol-triazole co-applications result in sensitization of seed- and foliar-associated plant pathogenic fungi, and if thymol affects production of fusarial toxins under field conditions.

Involvement of the Mitochondrial Protein Tyrosine Phosphatase PTPM1 in the Promotion of Conidiation, Development, and Pathogenicity in Colletotrichum graminicola

The phosphorylation status of proteins, which is determined by protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs), governs many cellular actions. In fungal pathogens, phosphorylation-mediated signal transduction has been considered to be one of the most important mechanisms in pathogenicity. Colletotrichum graminicola is an economically important corn pathogen. However, whether phosphorylation is involved in its pathogenicity is unknown. A mitochondrial protein tyrosine phosphatase gene, designated CgPTPM1, was deduced in C. graminicola through the use of bioinformatics and confirmed by enzyme activity assays and observation of its subcellular localization. We then created a CgPTPM1 deletion mutant (ΔCgPTPM1) to analyze its biological function. The results indicated that the loss of CgPTPM1 dramatically affected the formation of conidia and the development and differentiation into appressoria. However, the colony growth and conidial morphology of the ΔCgPTPM1 strains were unaffected. Importantly, the ΔCgPTPM1 mutant strains exhibited an obvious reduction of virulence, and the delayed infected hyphae failed to expand in the host cells. In comparison with the wild-type, ΔCgPTPM1 accumulated a larger amount of H2O2 and was sensitive to exogenous H2O2. Interestingly, the host cells infected by the mutant also exhibited an increased accumulation of H2O2 around the infection sites. Since the expression of the CgHYR1, CgGST1, CgGLR1, CgGSH1 and CgPAP1 genes was upregulated with the H2O2 treatment, our results suggest that the mitochondrial protein tyrosine phosphatase PTPM1 plays an essential role in promoting the pathogenicity of C. graminicola by regulating the excessive in vivo and in vitro production of H2O2.

A Novel Dual-Targeted α-Helical Peptide With Potent Antifungal Activity Against Fluconazole-Resistant Candida albicans Clinical Isolates

Due to compromised immune system, fungal infection incidences have markedly increased in the last few decades. Pathogenic fungi have developed resistance to the clinically available antifungal agents. Antifungal resistance poses a great challenge to clinical treatment and has stimulated the demand for novel antifungal agents. A promising alternative to the treatment of fungal diseases is the use of antimicrobial peptides (AMPs). However, the antifungal activities of AMPs have not been fully determined. Therefore, this study aimed at designing and screening α-helical peptides with potential antifungal activities. The effects of key physicochemical parameters on antifungal activities were also investigated. A series of lengthened and residue-substituted derivatives of the template peptide KV, a hexapeptide truncated from the α-helical region of porcine myeloid antimicrobial peptide-36, were designed and synthesized. Enhancement of hydrophobicity by introducing aromatic hydrophobic amino acids (tryptophan and phenylalanine) significantly increased the efficacies of the peptides against Candida albicans strains, including fluconazole-resistant isolates. Increased hydrophobicity also elevated the toxic properties of these peptides. RF3 with moderate hydrophobicity exhibited potent anticandidal activities (GM = 6.96 μM) and modest hemolytic activities (HC10 > 64 μM). Additionally, repeated exposure to a subinhibitory concentration of RF3 did not induce resistance development. The antifungal mechanisms of RF3 were due to membrane disruptions and induction of reactive oxygen species production. Such a dual-targeted mechanism was active against drug-resistant fungi. These results show the important role of hydrophobicity and provide new insights into designing and developing antifungal peptides. Meanwhile, the successful design of RF3 highlights the potential utility of AMPs in preventing the spread of drug-resistant fungal infections.

Impact of Escherichia coli infection in broiler breeder chicks: The effect of oxidative stress on weight gain

The aim of this study was to determine whether oxidative stress occurs in Escherichia coli-infected broiler breeder chicks, as well as the impact of this infection on bird growth. Twenty birds, 25-day-old female birds were divided into two groups (n = 10 per group): an intraperitoneally-infected group (1 mL containing 1.5 × 10⁸ CFU of E. coli) and a control group that received 1 mL of culture medium (uninfected birds). Birds were weighed individually at the beginning and at the end of the experiment, and samples were collected on days 0, 5 and 10 post-infection (PI). No clinical signs were observed throughout the experimental period; nevertheless, on day 10 PI, there was lower growth and weight gain in infected birds than in the control group. The infected birds showed pericarditis and liver congestion, as well as moderate periportal inflammatory infiltrates with predominance of neutrophils. Significantly higher numbers of total leukocytes, lymphocytes, heterophils and monocytes were observed in the infected group on days 5 and 10 PI, as well as significantly higher total protein and globulin levels; albumin values significantly decreased over the same period. Levels of serum oxidative biomarkers (lipid peroxidation (TBARS) and free radicals (ROS)) were significantly higher at 10 PI, as was glutathione S-transferase (GST) activity during the same period. Hepatic ROS and protein thiol levels were significantly higher in E. coli-infected birds, as well as activities of the antioxidant enzymes catalase, superoxide dismutase. In the spleen, only GST activity was significantly higher for the infected group, unlike the brain, where SOD activity, ROS and non-protein thiol levels were significantly higher in infected birds than in the control group. These data suggested that colibacillosis causes oxidative stress in broiler breeder chicks, negatively affecting their weight gain.

Transcriptional profiling of Scedosporium apiospermum enzymatic antioxidant gene battery unravels the involvement of thioredoxin reductases against chemical and phagocytic cells oxidative stress

Scedosporium species rank the second, after Aspergillus fumigatus, among the filamentous fungi colonizing the airways of patients with cystic fibrosis (CF). Development of microorganisms in the respiratory tract depends on their capacity to evade killing by the host immune system, particularly through the oxidative response of macrophages and neutrophils, with the release of reactive oxygen species (ROS) and reactive nitrogen species (RNS). This is particularly true in the airways of CF patients which display an exacerbated inflammatory reaction. To protect themselves, pathogens have developed various enzymatic antioxidant systems implicated in ROS degradation, including superoxide dismutases, catalases, cytochrome C peroxidases, chloroperoxidases and enzymes of the glutathione and thioredoxin systems, or in RNS degradation, that is, flavohemoglobins, nitrate reductases, and nitrite reductases. Here we investigated the transcriptional regulation of the enzymatic antioxidant gene battery in 24-h-old hyphae of Scedosporium apiospermum in response to oxidative stress induced chemically or by exposure to activated phagocytic cells. We showed that 21 out of the 33 genes potentially implicated in the oxidative or nitrosative stress response were overexpressed upon exposure of the fungus to various chemical oxidants, while they were only 13 in co-cultures with macrophages or neutrophils. Among them, genes encoding two thioredoxin reductases and to a lesser extent, a peroxiredoxin and one catalase were found to be overexpressed after chemical oxidative stress as well as in co-cultures. These results suggest that thioredoxin reductases, which are known to be virulence factors in other pathogenic fungi, play a key role in pathogenesis of scedosporiosis, and may be new drug targets.

Role of the antioxidant defense system during the production of lignocellulolytic enzymes by fungi

Fungi are used for the production of several compounds and the efficiency of biotechnological processes is directly related to the metabolic activity of these microorganisms. The reactions catalyzed by lignocellulolytic enzymes are oxidative and generate reactive oxygen species (ROS). Excess of ROS can cause serious damages to cells, including cell death. Thus, the objective of this work was to evaluate the lignocellulolytic enzymes produced by Pleurotus sajor-caju CCB020, Phanerochaete chrysosporium ATCC 28326, Trichoderma reesei RUT-C30, and Aspergillus niger IZ-9 grown in sugarcane bagasse and two yeast extract (YE) concentrations and characterize the antioxidant defense system of fungal cells by the activities of superoxide dismutase (SOD) and catalase (CAT). Pleurotus sajor-caju exhibited the highest activities of laccase and peroxidase in sugarcane bagasse with 2.6 g of YE and an increased activity of manganese peroxidase in sugarcane bagasse with 1.3 g of YE was observed. However, P. chrysosporium showed the highest activities of exoglucanase and endoglucanase in sugarcane bagasse with 1.3 g of YE. Lipid peroxidation and variations in SOD and CAT activities were observed during the production of lignocellulolytic enzymes and depending on the YE concentrations. The antioxidant defense system was induced in response to the oxidative stress caused by imbalances between the production and the detoxification of ROS.

Enzymatic Bioweathering and Metal Mobilization From Black Slate by the Basidiomycete Schizophyllum commune

Schizophyllum commune is a filamentous basidiomycete causing white-rot in many wood species with the help of a broad range of enzymes including multicopper oxidases such as laccases and laccase-like oxidases. Since these enzymes exhibit a broad substrate range, their ability to oxidatively degrade black slate was investigated. Both haploid monokaryotic, and mated dikaryotic strains were able to grow on black slate rich in organic carbon as sole carbon source. On defined media, only the monokaryon showed growth promotion by addition of slate. At the same time, metals were released from the slate and, after reaching a threshold concentration, inhibited further growth of the fungus. The proteome during decomposition of the black slate showed induction of proteins potentially involved in rock degradation and stress resistance, and the gene for laccase-like oxidase mco2 was up-regulated. Specifically in the dikaryon, the laccase gene lcc1 was induced, while lcc2 as well as mco1, mco3, and mco4 expression levels remained similar. Spectrophotometric analysis revealed that both life forms were able to degrade the rock and produce smaller particles.

Antioxidants Potential of the Filamentous Fungi (Mucor circinelloides)

Three important strains of Mucorcircinelloides grown in complete and minimal media for specified period (72 h, 120 h and 168 h) under submerged fermentation conditions were investigated for their potential antioxidants/secondary metabolite production. All mycelial extracts demonstrated effective antioxidant activities in terms of β-carotene/linoleic acid bleaching, radical scavenging, reduction of metal ions and chelating abilities against ferrous ions. Different extraction methods and solvent systems affected the recovery yield and antioxidant activities of the extracts significantly (p ≤ 0.05). Ethanolic extracts were found to be rich source of antioxidant components and subsequently more effective in antioxidant properties. Fermentation period and media used also significantly affected (p ≤ 0.05) the antioxidant production and the resulting antioxidant properties. The (ethanolic) extracts of all the strains from late exponential growth phase (120 h) showed highest antioxidant production with topmost reducing, chelating and radical scavenging capabilities. Strain MC277.49 was found to be the highest producer of antioxidants followed by MC108.16 and WJ11. Phenolic compounds were detected significantly in higher (p ≤ 0.05) amount succeeded by the condensed tannins and flavonoids. Total phenol content of each extract was attributed to overall antioxidant capacity. Submerged fermentation with nutritional stress conditions were found to be excellent way of producing surplus amount of natural antioxidants/secondary metabolites with their vast potential commercial application in food and pharmaceutical industries.

Proteomic Insights on the Metabolism of Penicillium janczewskii during the Biotransformation of the Plant Terpenoid Labdanolic Acid

Plant terpenoids compose a natural source of chemodiversity of exceptional value. Many of these compounds own biological/pharmacological activity, others are regarded as unique chemical skeletons for the synthesis of derivatives with improved properties. Functional chemical modification of terpenoids through biotransformation frequently relies on the use of Ascomycota strains, but information on major cellular responses is still largely lacking. Penicillium janczewskii mediates a stereo-selective hydroxylation of labdanolic acid (LA)-terpenoid found abundantly in Cistus ladanifer-producing 3β-hydroxy-labdanolic acid with yields >90%. Herein, combined analyses of mycelial and extracellular differential proteomes demonstrated that the plant terpenoid increased stress responses, especially against oxidative stress (e.g., accumulation of superoxide dismutase) and apparently altered mitochondria functioning. One putative cytochrome P450 monooxygenase differentially accumulated in the secretome and the terpenoid bioconversion was inhibited in vivo in the presence of a P450 inhibitor. The stereo-selective hydroxylation of the plant terpenoid is likely mediated by P450 enzymes, yet its unequivocal identity remains unclear. To the best of our knowledge, this is the first time that proteomics was used to investigate how a plant terpenoid impacts the metabolism of a filamentous fungus during its efficiently biotransformation. Our findings may encourage the development of new strategies for the valorization of plant natural resources through biotechnology.

Fusarium graminearum pyruvate dehydrogenase kinase 1 (FgPDK1) Is Critical for Conidiation, Mycelium Growth, and Pathogenicity

Pyruvate dehydrogenase kinase (PDK) is an important mitochondrial enzyme that blocks the production of acetyl-CoA by selectively inhibiting the activity of pyruvate dehydrogenase (PDH) through phosphorylation. PDK is an effectively therapeutic target in cancer cells, but the physiological roles of PDK in phytopathogens are largely unknown. To address these gaps, a PDK gene (FgPDK1) was isolated from Fusarium graminearum that is an economically important pathogen infecting cereals. The deletion of FgPDK1 in F. graminearum resulted in the increase in PDH activity, coinciding with several phenotypic defects, such as growth retardation, failure in perithecia and conidia production, and increase in pigment formation. The ΔFgPDK1 mutants showed enhanced sensitivity to osmotic stress and cell membrane-damaging agent. Physiological detection indicated that reactive oxygen species (ROS) accumulation and plasma membrane damage (indicated by PI staining, lipid peroxidation, and electrolyte leakage) occurred in ΔFgPDK1 mutants. The deletion of FgPDK1 also prohibited the production of deoxynivalenol (DON) and pathogenicity of F. graminearum, which may resulted from the decrease in the expression of Tri6. Taken together, this study firstly identified the vital roles of FgPDK1 in the development of phytopathogen F. graminearum, which may provide a potentially novel clue for target-directed development of agricultural fungicides.

Expression of Rice Mature Carbonic Anhydrase Gene Increase E. coli Tolerance to Heat Stress

Carbonic anhydrate is a zinc-containing metalloenzyme and involved in plant abiotic stress tolerance. In this study, we found that heat stress could induce rice mature carbonic anhydrate gene over-expression in rice plants. An Escherichia coli heterologous expression system was performed to identify the function of rice mature carbonic anhydrate in vitro. By sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), mature OsCA fusion protein was identified and proved to be soluble. The results of spot, survival rate, and growth curve assay demonstrated that the expression of the mature OsCA could enhance the thermo-tolerance of the induced mature OsCA recombinants in comparison with controls under heat stress. Meanwhile, compared with controls, the levels of reactive oxygen species in induced mature OsCA recombinants were apparently low under heat stress, and correspondingly, activities of the critical antioxidant enzymes including superoxide dismutase, catalase, and peroxidase in the induced mature OsCA recombinants were significantly increased. Additionally, relative to controls, the activity of the lactate dehydrogenase decreased in the induced mature OsCA recombinants under heat stress. Based on these results, we suggest that mature OsCA protein could confer the E. coli recombinants' tolerance to heat stress by a synergistic fashion of increasing the antioxidant enzymes' activities to reduce the oxidative damage and maintaining the lactate dehydrogenase (LDH) activity of E. coli.

An S-(hydroxymethyl)glutathione dehydrogenase is involved in conidiation and full virulence in the rice blast fungus Magnaporthe oryzae

Magnaporthe oryzae is a hemibiotrophic fungal pathogen that causes rice blast disease. A compatible interaction requires overcoming plant defense responses to initiate colonization during the early infection process. Nitric oxide (NO) plays important roles in defense responses during host-pathogen interactions. Microbes generally protect themselves against NO-induced damage by using enzymes. Here, we characterized an S-(hydroxymethyl)-glutathione dehydrogenase gene in M. oryzae, MoSFA1, the homologs of which are involved in NO metabolism by specifically catalyzing the reduction of S-nitrosoglutathione (GSNO) in yeasts and plants. As expected from the activities of S-(hydroxymethyl)glutathione dehydrogenase in formaldehyde detoxification and GSNO reduction, MoSFA1 deletion mutants were lethal in formaldehyde containing medium, sensitive to exogenous NO and exhibited a higher level of S-nitrosothiols (SNOs) than that of the wild type. Notably, the mutants showed severe reduction of conidiation and appressoria turgor pressure, as well as significantly attenuated the virulence on rice cultivar CO-39. However, the virulence of MoSFA1 deletion mutants on wounded rice leaf was not affected. An infection assay on barley leaf further revealed that MoSFA1 deletion mutants exhibited a lower infection rate, and growth of infectious hyphae of the mutants was retarded not only in primary infected cells but also in expansion from cell to cell. Furthermore, barley leaf cell infected by MoSFA1 deletion mutants exhibited a stronger accumulation of H2O2 at 24 and 36 hpi. MoSFA1 deletion mutants displayed hypersensitivity to different oxidants, reduced activities of superoxide dismutases and peroxidases, and lower glutathione content in cells, compared with the wild type. These results imply that MoSFA1-mediated NO metabolism is important in redox homeostasis in response to development and host infection of M. oryzae. Taken together, this work identifies that MoSFA1 is required for conidiation and contributes to virulence in the penetration and biotrophic phases in M. oryzae.

Oxidative stress response of Beauveria bassiana to Bordeaux mixture and its influence on fungus growth and development

BACKGROUND

Chemical fungicides used to manage plant diseases may negatively affect beneficial fungi such as entomopathogens. In this study, the participation of the antioxidative system in the entomopathogenic fungus Beauveria bassiana exposed to the copper-based Bordeaux mixture fungicide and its relation with fungus growth and development were examined. The fungus was grown in submerged culture containing Bordeaux mixture at the recommended dose. Within the first 24 h of elicitation, the vegetative growth, germination, sporulation and activity of amylase and laccase and the antioxidative enzymes catalase (CAT) and superoxide dismutase (SOD), as well as the production of hydrogen peroxide (H2 O2 ), were evaluated.

RESULTS

Bordeaux mixture inhibited B. bassiana germination (between 65 and 88%) and sporulation (between 15 and 57%) and significantly increased laccase production (≥130%), especially within the first 4 h of fungus exposure. By contrast, the mycelial growth was found to be less affected by the fungicide. These effects were accompanied with a significant increase in H2 O2 levels in fungal cells, as well as in SOD activity, but not in CAT, showing clear signs of increased oxidative stress.

CONCLUSION

The effect of Bordeaux mixture on B. bassiana development was probably due to the toxicity of the copper ion itself, and it also induced an oxidative state in fungal cells.

Toxicological and biochemical response of the entomopathogenic fungus Beauveria bassiana after exposure to deltamethrin

BACKGROUND

The chemical control of the Chagas disease vector Triatoma infestans is endangered by the emergence of pyrethroid resistance. An effective alternative control tool is the use of the entomopathogenic fungus Beauveria bassiana. The effect of deltamethrin on fungal growth, gene expression and enzyme activity in relation to detoxification, antioxidant response and oxidative stress levels was studied to evaluate fungal tolerance to deltamethrin.

RESULTS

The mean inhibitory concentration (IC50 ) was 50 µg deltamethrin/cm(2). Cytochrome P450 genes were differentially expressed; cyp52X1 and cyp617N1 transcripts were > 2-fold induced, followed by cyp655C1 (1.8-fold). Minor effects were observed on genes encoding for other P450s, epoxide hydrolase and glutathione S-transferase (GST). Superoxide dismutase (SOD) genes showed induction levels ≤ 2, catalase (CAT) and glutathione peroxidase genes were also induced ∼ 2-3-fold and < 2-fold, respectively. The activities of enzymes participating in the antioxidant defense system and phase II detoxification were also evaluated; SOD, CAT and GST activity showed significant differences with deltamethrin concentration. Lipid peroxidation levels and free proline content were also altered.

CONCLUSIONS

Beauveria bassiana GHA can be used combined with deltamethrin without significant metabolic detrimental effects. This combination will help optimizing the benefits and increasing the efficacy of vector control tools.

Robust anti-oxidant defences in the rice blast fungus Magnaporthe oryzae confer tolerance to the host oxidative burst

Plants respond to pathogen attack via a rapid burst of reactive oxygen species (ROS). However, ROS are also produced by fungal metabolism and are required for the development of infection structures in Magnaporthe oryzae. To obtain a better understanding of redox regulation in M. oryzae, we measured the amount and redox potential of glutathione (E(GSH)), as the major cytoplasmic anti-oxidant, the rates of ROS production, and mitochondrial activity using multi-channel four-dimensional (x,y,z,t) confocal imaging of Grx1-roGFP2 and fluorescent reporters during spore germination, appressorium formation and infection. High levels of mitochondrial activity and ROS were localized to the growing germ tube and appressorium, but E(GSH) was highly reduced and tightly regulated during development. Furthermore, germlings were extremely resistant to external H2O2 exposure ex planta. EGSH remained highly reduced during successful infection of the susceptible rice cultivar CO39. By contrast, there was a dramatic reduction in the infection of resistant (IR68) rice, but the sparse hyphae that did form also maintained a similar reduced E(GSH). We conclude that M. oryzae has a robust anti-oxidant defence system and maintains tight control of EGSH despite substantial oxidative challenge. Furthermore, the magnitude of the host oxidative burst alone does not stress the pathogen sufficiently to prevent infection in this pathosystem.

Glutathione levels in and total antioxidant capacity of Candida sp. cells exposed to oxidative stress caused by hydrogen peroxide

INTRODUCTION

The capacity to overcome the oxidative stress imposed by phagocytes seems to be critical for Candida species to cause invasive candidiasis.

METHODS

To better characterize the oxidative stress response (OSR) of 8 clinically relevant Candida sp., glutathione, a vital component of the intracellular redox balance, was measured using the 5,5'-dithiobis-(2-nitrobenzoic acid (DTNB)-glutathione disulfide (GSSG) reductase reconversion method; the total antioxidant capacity (TAC) was measured using a modified method based on the decolorization of the 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic) acid radical cation (ABTS*+). Both methods were used with cellular Candida sp. extracts treated or not with hydrogen peroxide (0.5 mM).

RESULTS

Oxidative stress induced by hydrogen peroxide clearly reduced intracellular glutathione levels. This depletion was stronger in Candida albicans and the levels of glutathione in untreated cells were also higher in this species. The TAC demonstrated intra-specific variation.

CONCLUSIONS

Glutathione levels did not correlate with the measured TAC values, despite this being the most important non-enzymatic intracellular antioxidant molecule. The results indicate that the isolated measurement of TAC does not give a clear picture of the ability of a given Candida sp. to respond to oxidative stress.

A role for antioxidants in acclimation of marine derived pathogenic fungus (NIOCC 1) to salt stress

Salinity tolerance a key factor helps in understanding the ionic homeostasis in general, which is a fundamental cellular phenomenon in all living cells. Here, a marine derived pathogenic fungus was examined for its adaptation under salt stress using antioxidant properties. The aqueous extracts of halophilic fungus exhibited different levels of antioxidant activity in all the in vitro tests such as α,α-diphenyl-β-picrylhydrazyl (DPPH(·)), Hydroxyl Radical Scavenging Assay (HRSA), Metal chelating assay and β-carotene-linoleic acid model system. The antioxidant capacity of marine fungus exposed to high salt condition showed an increase in activity. In addition, the production of intra and extracellular antioxidant enzymes of the fungus at various salt stresses were analyzed and discussed for their possible role in the stress mechanism. The marine derived fungus was identified as Phialosimplex genus, which is associated with infections in dogs. Thus the present study elucidates that the scavenging activity is one of the protective mechanisms developed in the fungus to avoid the deleterious effect of salt stress. In addition, the study also helps in understanding how the pathogenic fungus tackles the oxidative burst i.e. hypersensitivity reaction performed by host to kill the pathogens.

Comparative transcriptome analysis of the necrotrophic fungus Ascochyta rabiei during oxidative stress: insight for fungal survival in the host plant

Localized cell death, known as the hypersensitive response (HR), is an important defense mechanism for neutralizing phytopathogens. The hallmark of the HR is an oxidative burst produced by the host plant. We aimed to identify genes of the necrotrophic chickpea blight fungus Ascochyta rabiei that are involved in counteracting oxidative stress. A subtractive cDNA library was constructed after menadione treatment, which resulted in the isolation of 128 unigenes. A reverse northern blot was used to compare transcript profiles after H(2)O(2), menadione and sodium nitroprusside treatments. A total of 70 unigenes were found to be upregulated by more than two-fold following menadione treatment at different time intervals. A large number of genes not previously associated with oxidative stress were identified, along with many stress-responsive genes. Differential expression patterns of several genes were validated by quantitative real-time PCR (qRT-PCR) and northern blotting. In planta qRT-PCR of several selected genes also showed differential expression patterns during infection and disease progression. These data shed light on the molecular responses of the phytopathogen A. rabiei to overcome oxidative and nitrosative stresses and advance the understanding of necrotrophic fungal pathogen survival mechanisms.

Endobacteria affect the metabolic profile of their host Gigaspora margarita, an arbuscular mycorrhizal fungus

The aim of this paper was to understand whether the endobacterium identified as Candidatus Glomeribacter gigasporarum has an effect on the biology of its host, the arbuscular mycorrhizal fungus Gigaspora margarita, through the study of the modifications induced on the fungal proteome and lipid profile. The availability of G. margarita cured spores (i.e. spores that do not contain bacteria), represented a crucial tool to enable the comparison between two fungal homogeneous populations in the presence and the absence of the bacterial components. Our results demonstrate that the endobacterial presence leads to a modulation of fungal protein expression in all the different conditions we tested (quiescent, germinating and strigolactone-elicited germinating spores), and in particular after treatment with a strigolactone analogue. The fungal fatty acid profile resulted to be modified both quantitatively and qualitatively in the absence of endobacteria, being fatty acids less abundant in the cured spores. The results offer one of the first comparative metabolic studies of an AM fungus investigated under different physiological conditions, reveal that endobacteria have an important impact on the host fungal activity, influencing both protein expression and lipid profile, and suggest that the bacterial absence is perceived by G. margarita as a stimulus which activates stress-responsive proteins.

Heat-shock-induced oxidative stress and antioxidant response in Aspergillus niger 26

To extend the knowledge about the relationship between heat shock and oxidative stress in lower eukaryotes, the filamentous fungus Aspergillus niger 26 was chosen as a model system. Here, the response of A. niger cells to heat shock is reported. The temperature treatment significantly increased the levels of reactive oxygen species, superoxide anions (O2), and hydrogen peroxide and the rate of cyanide-resistant respiration as a marker of oxidative stress. Enhanced reactive oxygen species generation coincided with an increase in the content of oxidative damaged protein and in the accumulation of the storage carbohydrates trehalose and glycogen. Thermal survival of the A. niger cells corresponded to a significant increase in the levels of the antioxidant enzymes superoxide dismutase and catalase for all variants. These observations suggest that heat and oxidative stress have a common cellular effect.