Fungal-Metal Interactions: A Review of Toxicity and Homeostasis

Aspergillus fumigatus escape mechanisms from its harsh survival environments

Aspergillus fumigatus is a ubiquitous pathogenic mold and causes several diseases, including mycotoxicosis, allergic reactions, and systemic diseases (invasive aspergillosis), with high mortality rates. In its ecological niche, the fungus has evolved and mastered many reply strategies to resist and survive against negative threats, including harsh environmental stress and deficiency of essential nutrients from natural environments, immunity responses and drug treatments in host, and competition from symbiotic microorganisms. Hence, treating A. fumigatus infection is a growing challenge. In this review, we summarized A. fumigatus reply strategies and escape mechanisms and clarified the main competitive or symbiotic relationships between A. fumigatus, viruses, bacteria, or fungi in host microecology. Additionally, we discussed the contemporary drug repertoire used to treat A. fumigatus and the latest evidence of potential resistance mechanisms. This review provides valuable knowledge which will stimulate further investigations and clinical applications for treating and preventing A. fumigatus infections. KEY POINTS: • Harsh living environment was a great challenge for A. fumigatus survival. • A. fumigatus has evolved multiple strategies to escape host immune responses. • A. fumigatus withstands antifungal drugs via intrinsic escape mechanisms.

Glutathione-Mediated Metal Tolerance in an Amphibian Chytrid Fungus (Batrachochytrium dendrobatidis)

The spread of the amphibian chytrid fungus Batrachochytrium dendrobatidis, which causes the disease chytridiomycosis, has resulted in amphibian declines and extinctions worldwide. Some susceptible amphibian species can persist in contaminated habitats, prompting the hypothesis that B. dendrobatidis might be sensitive to heavy metals. We tested a panel of 12 metals to rank their toxicity to B. dendrobatidis zoospores and zoosporangia during a 6-h exposure. To better understand the mechanism for metal detoxification, we also evaluated whether glutathione is required for metal tolerance by depleting cellular glutathione before metal exposure. In addition, we investigated whether prior exposure to low metal concentrations impacted tolerance of subsequent exposure, as well as identifying metal combinations that may act synergistically. Silver (Ag), cadmium (Cd), and copper (Cu) were particularly toxic to B. dendrobatidis, with zoospore minimum lethal concentration values of 0.01 mM (Ag), 0.025 mM (Cd), and 0.5 mM (Cu). These three metals along with zinc (Zn) were also inhibitory to zoosporangia, with minimum inhibitory concentration values of 0.005 mM (Ag), 0.04 mM (Cd), 0.075 mM (Cu), and 0.04 mM (Zn). The fungicidal effects of several metals was reduced when assays were conducted in nutrient medium compared with synthetic pond water, highlighting the need for careful in vitro assay design and interpretation. Glutathione depletion strongly influenced tolerance of Cd and Ag (85% and 75% less growth, respectively) and moderately influenced tolerance of Cu, Zn, and lead (37%, 18%, and 14% less growth, respectively), indicating the importance of glutathione for metal detoxification. In general, the minimum metal concentrations that inhibited growth of B. dendrobatidis far exceeded values detected in contaminated amphibian habitats in Australia, suggesting that metal contamination alone may not have a strong protective effect against chytridiomycosis. We discuss future research directions to futher understand the potential for dissolved metals to create chytrid refuges. Environ Toxicol Chem 2024;43:1583-1591. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Biochemical Behavior, Influence on Cell DNA Condition, and Microbiological Properties of Wool and Wool-Copper Materials

The paper presents the study concerning the preparation and physio-chemical and biological properties of wool-copper (WO-Cu) materials obtained by the sputter deposition of copper onto the wool fibers. The WO-Cu material was subjected to physio-chemical and biological investigations. The physio-chemical investigations included the elemental analysis of materials (C, N, O, S, and Cu), their microscopic analysis, and surface properties analysis (specific surface area and total pore volume). The biological investigations consisted of the antimicrobial activity tests of the WO-Cu materials against colonies of Gram-positive (Staphylococcus aureus) bacteria, Gram-negative (Escherichia coli) bacteria, and fungal mold species (Chaetomium globosum). Biochemical-hematological tests included the evaluation of the activated partial thromboplastin time and pro-thrombin time. The tested wool-copper demonstrated the ability to interact with the DNA in a time-dependent manner. These interactions led to the DNA's breaking and degradation. The antimicrobial and antifungal activities of the WO-Cu materials suggest a potential application as an antibacterial/antifungal material. Wool-copper materials may be also used as customized materials where the blood coagulation process could be well controlled through the appropriate copper content.

A Potential Involvement of Metallothionein in the Zinc Tolerance of Trichoderma harzianum: Experimental Findings

Metallothioneins are a group of cysteine-rich proteins that play an important role in the homeostasis and detoxification of heavy metals. The objective of this research was to explore the significance of metallothionein in Trichoderma harzianum tolerance to zinc. At the inhibitory concentration of 1000 ppm, the fungus adsorbed 16.7 ± 0.4 mg/g of metal. The HPLC and SDS-PAGE electrophoresis data suggested that the fungus production of metallothionein was twice as high in the presence of zinc as in the control group. The examination of the genes; metallothionein expression activator (MEA) and Cu fist revealed that the MEA, with a C2H2 zinc finger domain, increased significantly in the presence of zinc. It was observed that in T. harzianum, the enhanced expression of the metallothionein gene was managed by the metallothionein activator under zinc overload conditions. According to our knowledge, this is the first report on the role of metallothionein in the resistance of T. harzianum to zinc.

Evaluation of multi-heavy metal tolerance traits of soil-borne fungi for simultaneous removal of hazardous metals

The demand for environment-friendly cleanup techniques has arisen due to an increase in environmental pollutants. Fungi is the most prevalent and effective class of heavy metal-resistant microorganisms with the ability to leach metals. The objective of the present study was to isolate the fungi from the agricultural soil of Kashmir valley, investigate their multi-metal tolerance to heavy metals and evaluate the metal uptake capacities of the resistant fungi. The fungi were isolated and identified on the basis of morphological and molecular approach (ITS1 and ITS4). The tolerance limits of the isolated fungal strains to various doses of lead (Pb), cadmium (Cd), zinc (Zn), chromium (Cr), copper (Cu), nickel (Ni), and cobalt (Co) was evaluated. Five fungal strains, Aspergillus niger, Fusarium oxysporum, Fusarium verticillioides, Aspergillus fischeri, Epicoccum mackenziei were isolated from the soil samples. To the best of our knowledge, this is the first report on the study of metal resistance of Aspergillus fischeri and Epicoccum mackenziei. Among the identified fungal species, Aspergillus niger and Fusarium oxysporum were found to be most tolerant with a minimum inhibitory concentration (MIC) of 600 ppm against Cu and Cr respectively. Results indicated removal of considerable amount of heavy metals by some of the fungi. The highest metal uptake of 8.31 mg/g was found in Fusarium verticillioides for Zn. Surprisingly, these fungal strains demonstrated resistance to metal concentrations above the levels that are universally acceptable for polluted soils, and hence prove to be appealing contenders for use as bioremediation agents for cleaning up heavy metal-polluted environments.

Poacic Acid, a Plant-Derived Stilbenoid, Augments Cell Wall Chitin Production, but Its Antifungal Activity Is Hindered by This Polysaccharide and by Fungal Essential Metals

Climate and environmental changes have modified the habitats of fungal pathogens, inflicting devastating effects on livestock and crop production. Additionally, drug-resistant fungi are increasing worldwide, driving the urgent need to identify new molecular scaffolds for the development of antifungal agents for humans, animals, and plants. Poacic acid (PA), a plant-derived stilbenoid, was recently discovered to be a novel molecular scaffold that inhibits the growth of several fungi. Its antifungal activity has been associated with perturbation of the production/assembly of the fungal cell wall β-1,3-glucan, but its mode of action is not resolved. In this study, we investigated the antifungal activity of PA and its derivatives on a panel of yeast. PA had a fungistatic effect on S. cerevisiae and a fungicidal effect on plasma membrane-damaged Candida albicans mutants. Live cell fluorescence microscopy experiments revealed that PA increases chitin production and modifies its cell wall distribution. Chitin production and cell growth returned to normal after prolonged incubation. The antifungal activity of PA was reduced in the presence of exogenous chitin, suggesting that the potentiation of chitin production is a stress response that helps the yeast cell overcome the effect of this antifungal stilbenoid. Growth inhibition was also reduced by metal ions, indicating that PA affects the metal homeostasis. These findings suggest that PA has a complex antifungal mechanism of action that involves perturbation of the cell wall β-1,3-glucan production/assembly, chitin production, and metal homeostasis.

Unravelling the Mechanisms of Heavy Metal Tolerance: Enhancement in Hydrophilic Antioxidants and Major Antioxidant Enzymes Is Not Crucial for Long-Term Adaptation to Copper in Chlamydomonas reinhardtii

Understanding of the mechanisms of heavy metal tolerance in algae is important for obtaining strains that can be applied in wastewater treatment. Cu is a redox-active metal directly inducing oxidative stress in exposed cells. The Cu-tolerant Chlamydomonas reinhardtii strain Cu2, obtained via long-term adaptation, displayed increased guaiacol peroxidase activity and contained more lipophilic antioxidants, i.e., α-tocopherol and plastoquinol, than did non-tolerant strain N1. In the present article, we measured oxidative stress markers; the content of ascorbate, soluble thiols, and proline; and the activity of superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX) in N1 and Cu2 strains grown in the absence or presence of excessive Cu. The Cu2 strain displayed less pronounced lipid peroxidation and increased APX activity compared to N1. The amount of antioxidants was similar in both strains, while SOD and CAT activity was lower in the Cu2 strain. Exposure to excessive Cu led to a similar increase in proline content in both strains and a decrease in ascorbate and thiols, which was more pronounced in the N1 strain. The Cu2 strain was less tolerant to another redox-active heavy metal, namely chromium. Apparently other mechanisms, probably connected to Cu transport, partitioning, and chelation, are more important for Cu tolerance in Cu2 strain.

Cellular Internalization and Toxicity of Chitosan Nanoparticles Loaded with Nobiletin in Eukaryotic Cell Models (Saccharomyces cerevisiae and Candida albicans)

This study involved the synthesis and characterization of chitosan nanoparticles loaded with nobiletin (CNpN) and assessed their toxicity and cellular internalization in eukaryotic cell models (Saccharomyces cerevisiae and Candida albicans). Nanoparticles were prepared via the nanoprecipitation method and physicochemically characterized to determine their hydrodynamic diameter using dynamic light scattering (DLS), their surface charge through ζ-potential measurements, and their chemical structure via Fourier-transform infrared spectroscopy (FTIR). The hydrodynamic diameter and ζ-potential of chitosan nanoparticles (CNp) and CNpN were found to be 288.74 ± 2.37 nm and 596.60 ± 35.49 nm, and 34.51 ± 0.66 mV and 37.73 ± 0.19 mV, respectively. The scanning electron microscopy (SEM) images displayed a particle size of approximately 346 ± 69 nm, with notable sphericity for CNpN. FTIR analysis provided evidence of potential imine bonding between chitosan and nobiletin. Membrane integrity damage could be observed in both S. cerevisiae and C. albicans yeast stained with propidium iodide, demonstrating membrane integrity damage caused by CNp and CNpN, where higher concentration treatments inhibited the development of yeast cells. These findings suggest a selective therapeutic potential of CNpN, which could be promising for the development of antifungal and anticancer therapies. This study contributes to understanding the interaction between nanoparticles and eukaryotic cells, offering insights for future biomedical applications.

Microbial removal of nutrients from anaerobic digestate: assessing product-coupled and non-product-coupled approaches

Although anaerobic digestate contains >90% water, the high nutrient content of digestate makes it economically and technically intractable to treatment by existing wastewater treatment technologies. This study separately assessed the feasibility of nutrient removal from digestate by Rhizopus delemar DSM 905 and a culture of phosphate-accumulating organisms (PAOs). With Rhizopus delemar DSM 905, we investigated concomitant nutrient removal from digestate-supplemented medium and fumaric acid production, as a potentially economical strategy for digestate treatment. Following the cultivation of R. delemar DSM 905 in a fermentation medium containing 25% (v/v) digestate, the concentrations of Al, Cr, Cu, Fe, K, Mg, Mn, Pb, and Zn reduced 40, 12, 74, 96, 12, 26, 23%, ~18, and 28%, respectively. Similarly, the concentrations of total phosphorus, total nitrogen, phosphate (PO4-P), ammonium (NH4-N), nitrate (NO3-N), and sulfur decreased 93, 88, 97, 98, 69, and 13%, respectively. Concomitantly, cultures supplemented with 25 and 15% (v/v) digestate produced comparable titers of fumarate (~11 and ~ 17 g/L, respectively) to the digestate un-supplemented control cultures. With PAOs, we assessed the removal of total phosphorus, total nitrogen, PO4-P, and NH4-N, of which the concentrations reduced 86, 90%, ~99, and 100%, respectively in 60% (v/v) digestate. This study provides additional bases for microbial removal of excess nutrients from anaerobic digestate, with the potential to engender future water recovery from this waste stream that is currently largely recalcitrant to treatment.

Physiological response mechanism of heavy metal-resistant endophytic fungi isolated from the roots of Polygonatum kingianum

This study aims to evaluate the tolerance of endophytic fungi isolated from the fibrous roots of Polygonatum kingianum to arsenic (As) and cadmium (Cd) and their physiological response mechanisms. Five isolated strains were obtained with EC50 values for As(V) ranging from 421 to 1281 mg/L, while the other three strains tolerated Cd(II) with an EC50 range of 407-1112 mg/L. Morphological and molecular identification indicated that these eight strains were Cladosporium spp. belonging to dark septate endophytes (DSEs). The contents of metal ions in mycelium sharply increased, reaching 38.87 mg/kg for strain MZ-11 under As(V) stress and 0.33 mg/kg for fungus PR-2 under Cd(II). The physiological response revealed that the biomass decreased with increasing concentrations of As(V) or Cd(II), and the activity of superoxide dismutase significantly improved under the corresponding EC50 -concentration As/Cd of the strains, as well as the contents of antioxidant substances, including metallothionein, glutathione, malondialdehyde, melanin, and proline. Taken together, the filamentous fungi of Cladosporium spp. accounted for a high proportion of fungi isolated from the fibrous roots of P. kingianum and had a strong capacity to tolerate As(V) or Cd(II) stress by improving antioxidase activities and the content of antioxidant substances, and immobilization of metal ions in hyphae.

Antifungal mechanism of volatile compounds emitted by Actinomycetota Paenarthrobacter ureafaciens from a disease-suppressive soil on Saccharomyces cerevisiae

Increasing evidence suggests that in disease-suppressive soils, microbial volatile compounds (mVCs) released from bacteria may inhibit the growth of plant-pathogenic fungi. However, the antifungal activities and molecular responses of fungi to different mVCs remain largely undescribed. In this study, we first evaluated the responses of pathogenic fungi to treatment with mVCs from Paenarthrobacter ureafaciens. Then, we utilized the well-characterized fungal model organism Saccharomyces cerevisiae to study the potential mechanistic effects of the mVCs. Our data showed that exposure to P. ureafaciens mVCs leads to reduced growth of several pathogenic fungi, and in yeast cells, mVC exposure prompts the accumulation of reactive oxygen species. Further experiments with S. cerevisiae deletion mutants indicated that Slt2/Mpk1 and Hog1 MAPKs play major roles in the yeast response to P. ureafaciens mVCs. Transcriptomic analysis revealed that exposure to mVCs was associated with 1,030 differentially expressed genes (DEGs) in yeast. According to gene ontology and Kyoto Encyclopedia of Genes and Genomes analyses, many of these DEGs are involved in mitochondrial dysfunction, cell integrity, mitophagy, cellular metabolism, and iron uptake. Genes encoding antimicrobial proteins were also significantly altered in the yeast after exposure to mVCs. These findings suggest that oxidative damage and mitochondrial dysfunction are major contributors to the fungal toxicity of mVCs. Furthermore, our data showed that cell wall, antioxidant, and antimicrobial defenses are induced in yeast exposed to mVCs. Thus, our findings expand upon previous research by delineating the transcriptional responses of the fungal model. IMPORTANCE Since the use of bacteria-emitted volatile compounds in phytopathogen control is of considerable interest, it is important to understand the molecular mechanisms by which fungi may adapt to microbial volatile compounds (mVCs). Paenarthrobacter ureafaciens is an isolated bacterium from disease-suppressive soil that belongs to the Actinomycetota phylum. P. ureafaciens mVCs showed a potent antifungal effect on phytopathogens, which may contribute to disease suppression in soil. However, our knowledge about the antifungal mechanism of mVCs is limited. This study has proven that mVCs are toxic to fungi due to oxidative stress and mitochondrial dysfunction. To deal with mVC toxicity, antioxidants and physical defenses are required. Furthermore, iron uptake and CAP proteins are required for antimicrobial defense, which is necessary for fungi to deal with the thread from mVCs. This study provides essential foundational knowledge regarding the molecular responses of fungi to inhibitory mVCs.

Benzamidine Conjugation Converts Expelled Potential Active Agents into Antifungals against Drug-Resistant Fungi

Fungal infections present a growing global public health concern, necessitating the development of novel antifungal drugs. However, many potential antifungals, particularly the expelled potential active agents (EPAAs), are often underestimated owing to their limitations in cellular entry or expulsion by efflux pumps. Herein, we identified 68 EPAAs out of 2322 candidates with activity against a Candida albicans efflux pump-deficient strain and no inhibitory activity against the wild-type strain. Using a novel conjugation strategy involving benzamidine (BM) as a mitochondrion-targeting warhead, we successfully converted EPAAs into potent antifungals against various urgent-threat azole-resistantCandida strains. Among the obtained EPAA-BM conjugates, IS-2-BM (11) exhibited excellent antifungal activities and induced negligible drug resistance. Furthermore, IS-2-BM prevented biofilm formation, eradicated mature biofilms, and exhibited excellent therapeutic effects in a murine model of systemic candidiasis. These findings provide a promising strategy for increasing the possibilities of discovering more antifungals.

A First Report of Sclerotinia sclerotiorum Causing Forsythia Twig Blight in Romania

Sclerotinia sclerotiorum (Lib.) de Bary (1884) is a fungal plant pathogen with worldwide distribution and a varying host range from different botanical families. It can cause damage to a large variety of crops such as sunflower, soybean, dry bean, canola, some vegetables, and ornamental plants. This article reports the occurrence of twig blight on the forsythia plant from the NE region of Romania. The disease was observed on Forsythia × intermedia Zab. plants from the Arboretum Park of the Iasi University of Life Sciences (IULS), located in Iasi City, Romania. Infected tissue was investigated through morphological characteristics using Sanger sequencing. Genomic DNA was extracted from the isolate obtained from naturally infected plants, and the ribosomal internal transcribed spacer region was amplified using the ITS1, ITS2, and LSU D1 and D2. Based on the results of this study, molecular and morphological data suggest that Forsythia twig blight can be caused by S. sclerotiorum. Constant monitoring of Sclerotinia sclerotiorum across multiple hosts and time intervals will reduce potential spread and future economic losses in cultivated species.

Fungal Elicitation Enhances Vincristine and Vinblastine Yield in the Embryogenic Tissues of Catharanthus roseus

Fungal elicitation could improve the secondary metabolite contents of in vitro cultures. Herein, we report the effect of Fusarium oxysporum on vinblastine and vincristine alkaloid yields in Catharanthus roseus embryos. The study revealed increased yields of vinblastine and vincristine in Catharanthus tissues. Different concentrations, i.e., 0.05% (T1), 0.15% (T2), 0.25% (T3), and 0.35% (T4), of an F. oxysporum extract were applied to a solid MS medium in addition to a control (T0). Embryogenic calli were formed from the hypocotyl explants of germinating seedlings, and the tissues were exposed to Fusarium extract elicitation. The administration of the F. oxysporum extract improved the growth of the callus biomass, which later differentiated into embryos, and the maximum induction of somatic embryos was noted T2 concentration (102.69/callus mass). A biochemical analysis revealed extra accumulations of sugar, protein, and proline in the fungus-elicitated cultivating tissues. The somatic embryos germinated into plantlets on full-strength MS medium supplemented with 2.24 µM of BA. The germination rate of the embryos and the shoot and root lengths of the embryos were high at low doses of the Fusarium treatment. The yields of vinblastine and vincristine were measured in different treated tissues via high-pressure thin-layer chromatography (HPTLC). The yield of vinblastine was high in mature (45-day old) embryos (1.229 µg g-1 dry weight), which were further enriched (1.267 µg g-1 dry weight) via the F. oxysporum-elicitated treatment, especially at the T2 concentration. Compared to vinblastine, the vincristine content was low, with a maximum of 0.307 µg g-1 dry weight following the addition of the F. oxysporum treatment. The highest and increased yields of vinblastine and vincristine, 7.88 and 15.50%, were noted in F. oxysporum-amended tissues. The maturated and germinating somatic embryos had high levels of SOD activity, and upon the addition of the fungal extracts, the enzyme's activity was further elevated, indicating that the tissues experienced cellular stress which yielded increased levels of vinblastine and vincristine following the T2/T1 treatments. The improvement in the yields of these alkaloids could augment cancer healthcare treatments, making them easy, accessible, and inexpensive.

Iron and copper on Botrytis cinerea: new inputs in the cellular characterization of their inhibitory effect

Certain metals play key roles in infection by the gray mold fungus, Botrytis cinerea. Among them, copper and iron are necessary for redox and catalytic activity of enzymes and metalloproteins, but at high concentrations they are toxic. Understanding the mechanism requires more cell characterization studies for developing new, targeted metal-based fungicides to control fungal diseases on food crops. This study aims to characterize the inhibitory effect of copper and iron on B. cinerea by evaluating mycelial growth, sensitivity to cell wall perturbing agents (congo red and calcofluor white), membrane integrity, adhesion, conidial germination, and virulence. Tests of copper over the range of 2 to 8 mM and iron at 2 to 20 mM revealed that the concentration capable of reducing mycelial growth by 50% (IC50) was 2.87 mM and 9.08 mM for copper and iron, respectively. When mixed at equimolar amounts there was a significant inhibitory effect mostly attributable to copper. The effect of Cu50, Fe50, and Cu50-Fe50 was also studied on the mycelial growth of three wild B. cinerea strains, which were more sensitive to metallic inhibitors. A significant inhibition of conidial germination was correlated with adhesion capacity, indicating potential usefulness in controlling disease at early stages of crop growth. Comparisons of the effects of disruptive agents on the cell wall showed that Cu, Fe, and Cu-Fe did not exert their antifungal effect on the cell wall of B. cinerea. However, a relevant effect was observed on plasma membrane integrity. The pathogenicity test confirmed that virulence was correlated with the individual presence of Cu and Fe. Our results represent an important contribution that could be used to formulate and test metal-based fungicides targeted at early prevention or control of B. cinerea.

A comprehensive review on potential applications of metallic nanoparticles as antifungal therapies to combat human fungal diseases

Human pathogenic fungi are responsible for causing a range of infection types including mucosal, skin, and invasive infections. Life-threatening and invasive fungal infections (FIs) are responsible for mortality and morbidity, especially for individuals with compromised immune function. The number of currently available therapeutic agents against invasive FIs is limited compared to that against bacterial infections. In addition, the increased mortality and morbidity caused by FIs are linked to the limited number of available antifungal agents, antifungal resistance, and the increased toxicity of these agents. Currently available antifungal agents have several drawbacks in efficiency, efficacy, toxicity, activity spectrum, and selectivity. It has already been demonstrated with numerous metallic nanoparticles (MNPs) that these nanoparticles can serve as an effective and alternative solution as fungicidal agents. MNPs have great potential owing to their intrinsic antifungal properties and potential to deliver antifungal drugs. For instance, gold nanoparticles (AuNPs) have the capacity to disturb mitochondrial calcium homeostasis induced AuNP-mediated cell death in Candida albicans. In addition, both copper nanoparticles and copper oxide nanoparticles exerted significant suppressive properties against pathogenic fungi. Silver nanoparticles showed strong antifungal properties against numerous pathogenic fungi, such as Stachybotrys chartarum, Mortierella alpina, Chaetomium globosum, A. fumigatus, Cladosporium cladosporioides, Penicillium brevicompactum, Trichophyton rubrum, C. tropicalis, and C. albicans. Iron oxide nanoparticles showed potent antifungal activities against A. niger and P. chrysogenum. It has also been reported that zinc oxide nanoparticles can significantly inhibit fungal growth. These NPs have already exerted potent antifungal properties against a number of pathogenic fungal species including Candida, Aspergillus, Fusarium, and many others. Several strategies are currently used for the research and development of antifungal NPs including chemical modification of NPs and combination with the available drugs. This review has comprehensively presented the current and innovative antifungal approach using MNPs. Moreover, different types of MNPs, their physicochemical characteristics, and production techniques have been summarized in this review.

Metals and the cell surface of Cryptococcus neoformans

Recent studies in pathogenic yeasts reinforce our appreciation of the influence of metal homeostasis on the fungal cell surface. To illustrate this influence, we focus on recent studies on Cryptococcus neoformans, a fungal pathogen with a complex surface of a cell wall with embedded melanin and an attached polysaccharide capsule. Copper and iron are essential yet toxic metals, and current efforts demonstrate the importance of these metals for modulating the surface structure of C. neoformans cells in ways that contribute to fungal-host interactions during disease in vertebrate hosts. In this review, we briefly summarize mechanisms of acquisition and regulation for copper and iron, and then discuss recent insights into the connections between the metals and the cell surface.

Double- or Triple-Tiered Protection: Prospects for the Sustainable Application of Copper-Based Antimicrobial Compounds for Another Fourteen Decades

Copper (Cu)-based antimicrobial compounds (CBACs) have been widely used to control phytopathogens for nearly fourteen decades. Since the first commercialized Bordeaux mixture was introduced, CBACs have been gradually developed from highly to slightly soluble reagents and from inorganic to synthetic organic, with nanomaterials being a recent development. Traditionally, slightly soluble CBACs form a physical film on the surface of plant tissues, separating the micro-organisms from the host, then release divalent or monovalent copper ions (Cu²⁺ or Cu⁺) to construct a secondary layer of protection which inhibits the growth of pathogens. Recent progress has demonstrated that the release of a low concentration of Cu²⁺ may elicit immune responses in plants. This supports a triple-tiered protection role of CBACs: break contact, inhibit microorganisms, and stimulate host immunity. This spatial defense system, which is integrated both inside and outside the plant cell, provides long-lasting and broad-spectrum protection, even against emergent copper-resistant strains. Here, we review recent findings and highlight the perspectives underlying mitigation strategies for the sustainable utilization of CBACs.

Structures and coordination chemistry of transporters involved in manganese and iron homeostasis

A repertoire of transporters plays a crucial role in maintaining homeostasis of biologically essential transition metals, manganese, and iron, thus ensuring cell viability. Elucidating the structure and function of many of these transporters has provided substantial understanding into how these proteins help maintain the optimal cellular concentrations of these metals. In particular, recent high-resolution structures of several transporters bound to different metals enable an examination of how the coordination chemistry of metal ion-protein complexes can help us understand metal selectivity and specificity. In this review, we first provide a comprehensive list of both specific and broad-based transporters that contribute to cellular homeostasis of manganese (Mn2+) and iron (Fe2+ and Fe3+) in bacteria, plants, fungi, and animals. Furthermore, we explore the metal-binding sites of the available high-resolution metal-bound transporter structures (Nramps, ABC transporters, P-type ATPase) and provide a detailed analysis of their coordination spheres (ligands, bond lengths, bond angles, and overall geometry and coordination number). Combining this information with the measured binding affinity of the transporters towards different metals sheds light into the molecular basis of substrate selectivity and transport. Moreover, comparison of the transporters with some metal scavenging and storage proteins, which bind metal with high affinity, reveal how the coordination geometry and affinity trends reflect the biological role of individual proteins involved in the homeostasis of these essential transition metals.

Identification and Characterization of Dmct: A Cation Transporter in Yarrowia lipolytica Involved in Metal Tolerance

Yarrowia lipolytica is a dimorphic fungus used as a model organism to investigate diverse biotechnological and biological processes, such as cell differentiation, heterologous protein production, and bioremediation strategies. However, little is known about the biological processes responsible for cation concentration homeostasis. Metals play pivotal roles in critical biochemical processes, and some are toxic at unbalanced intracellular concentrations. Membrane transport proteins control intracellular cation concentrations. Analysis of the Y. lipolytica genome revealed a characteristic functional domain of the cation efflux protein family, i.e., YALI0F19734g, which encodes YALI0F19734p (a putative Yl-Dmct protein), which is related to divalent metal cation tolerance. We report the in silico analysis of the putative Yl-Dmct protein's characteristics and the phenotypic response to divalent cations (Ca²⁺, Cu²⁺, Fe²⁺, and Zn²⁺) in the presence of mutant strains, Δdmct and Rdmct, constructed by deletion and reinsertion of the DMCT gene, respectively. The absence of the Yl-Dmct protein induces cellular and growth rate changes, as well as dimorphism differences, when calcium, copper, iron, and zinc are added to the cultured medium. Interestingly, the parental and mutant strains were able to internalize the ions. Our results suggest that the protein encoded by the DMCT gene is involved in cell development and cation homeostasis in Y. lipolytica.

Synergistic Antifungal Interaction between Pseudomonas aeruginosa LV Strain Metabolites and Biogenic Silver Nanoparticles against Candida auris

Candida auris has been found to be a persistent colonizer of human skin and a successful pathogen capable of causing potentially fatal infection, especially in immunocompromised individuals. This fungal species is usually resistant to most antifungal agents and has the ability to form biofilms on different surfaces, representing a significant therapeutic challenge. Herein, the effect of metabolites of Pseudomonas aeruginosa LV strain, alone and combined with biologically synthesized silver nanoparticles (bioAgNP), was evaluated in planktonic and sessile (biofilm) cells of C. auris. First, the minimal inhibitory and fungicidal concentration values of 3.12 and 6.25 μg/mL, respectively, were determined for F4a, a semi-purified bacterial fraction. Fluopsin C and indolin-3-one seem to be the active components of F4a. Like the semi-purified fraction, they showed a time- and dose-dependent fungicidal activity. F4a and bioAgNP caused severe changes in the morphology and ultrastructure of fungal cells. F4a and indolin-3-one combined with bioAgNP exhibited synergistic fungicidal activity against planktonic cells. F4a, alone or combined with bioAgNP, also caused a significant decrease in the number of viable cells within the biofilms. No cytotoxicity to mammalian cells was detected for bacterial metabolites combined with bioAgNP at synergistic concentrations that presented antifungal activity. These results indicate the potential of F4a combined with bioAgNP as a new strategy for controlling C. auris infections.

The YBR056W-A and Its Ortholog YDR034W-B of S. cerevisiae Belonging to CYSTM Family Participate in Manganese Stress Overcoming

The CYSTM (cysteine-rich transmembrane module) protein family comprises small molecular cysteine-rich tail-anchored membrane proteins found in many eukaryotes. The Saccharomyces cerevisiae strains carrying the CYSTM genes YDRO34W-B and YBR056W-A (MNC1) fused with GFP were used to test the expression of these genes under different stresses. The YBR056W-A (MNC1) and YDR034W-B genes are expressed under stress conditions caused by the toxic concentrations of heavy metal ions, such as manganese, cobalt, nickel, zinc, cuprum, and 2.4-dinitrophenol uncoupler. The expression level of YDR034W-B was higher than that of YBR056W-A under alkali and cadmium stresses. The Ydr034w-b-GFP and Ybr056w-a-GFP proteins differ in the cellular localization: Ydr034w-b-GFP was mainly observed in the plasma membrane and vacuolar membrane, while Ybr056w-a-GFP was observed in the cytoplasm, probably in intracellular membranes. The null-mutants in both genes demonstrated decreased cell concentration and lytic phenotype when cultivated in the presence of excess manganese. This allows for speculations about the involvement of Mnc1 and Ydr034w-b proteins in manganese stress overcoming.

The Unusual Dominance of the Yeast Genus Glaciozyma in the Deeper Layer in an Antarctic Permafrost Core (Adélie Cove, Northern Victoria Land) Is Driven by Elemental Composition

Rock glaciers are relatively common in Antarctic permafrost areas and could be considered postglacial cryogenic landforms. Although the extensive presence of rock glaciers, their chemical–physical and biotic composition remain scarce. Chemical–physical parameters and fungal community (by sequencing the ITS2 rDNA, Illumina MiSeq) parameters of a permafrost core were studied. The permafrost core, reaching a depth of 6.10 m, was divided into five units based on ice content. The five units (U1–U5) of the permafrost core exhibited several significant (p < 0.05) differences in terms of chemical and physical characteristics, and significant (p < 0.05) higher values of Ca, K, Li, Mg, Mn, S, and Sr were found in U5. Yeasts dominated on filamentous fungi in all the units of the permafrost core; additionally, Ascomycota was the prevalent phylum among filamentous forms, while Basidiomycota was the dominant phylum among yeasts. Surprisingly, in U5 the amplicon sequence variants (ASVs) assigned to the yeast genus Glaciozyma represented about two-thirds of the total reads. This result may be considered extremely rare in Antarctic yeast diversity, especially in permafrost habitats. Based on of the chemical–physical composition of the units, the dominance of Glaciozyma in the deepest unit was correlated with the elemental composition of the core.

Bivalent copper ions presence triggers removal and homeostatic mechanisms in the metal-resistant microorganism Apiotrichum loubieri M12

Microorganisms, especially those habiting mining environments, are of great importance for the retention of toxic metals in the environment. This work aimed to isolate a copper removing-microorganism from sediments of an Acid Mine Drainage-affected environment and to study the cellular responses trigger by metal presence. Apiotrichum loubieri M12 was able to tolerate and remove Cu(II) from liquid culture media, reaching a 30-35% removal capacity when it was exposed to 40 μg mL^-1 Cu(II) after 48 h. Analysis of the biomass exposed to the metal through SEM-EDS showed copper presence on the cell surface and variations in the proportion of other biomass constituent elements. Proteomics revealed that the presence of Cu(II) induces differential expression of intracellular proteins involved in a wide variety of metabolic processes. Interestingly, a specific response to the metal was detected in cell-free supernatants, in which copper binding proteins were identified. A large number of proteins with metal ion binding sites were detected both at intra and extracellular levels. The microorganism responds not only by adjusting intracellular protein expression, but also by adjusting expression of proteins in the extracellular space.

Bioremediation of copper using indigenous fungi Aspergillus species isolated from an abandoned copper mine soil

Bioremediation of mining soils using metal tolerant fungi is widely considered as a promising cost-effective and ecofriendly approach. This study assessed the copper removal efficiency and bioaccumulation ability of the indigenous species Aspergillus hiratsukae LF1 and Aspergillus terreus LF2 isolated from the soils of an abandoned copper mine in Oman. Nutrient medium containing five different Cu (II) levels (0 - control, 100, 200, 300 and 500 mg/L) was employed for assessing both parameters. The removal efficiency from nutrient medium (100-500 mg Cu per L) ranged from 57% to 21% for A. hiratsukae LF1, and from 69% to 24% for A. terreus LF2. A. hiratsukae LF1 and A. terreus LF2 accumulated a maximum of 4.63 and 5.95 mg Cu/g,espectively, at 500 mg/L of Cu (II) concentration. The compositional analysis of extracellular polymeric substances excreted by both species revealed a hormetic response by A. hiratsukae LF1 at 100 mg/L; whereas increasing media Cu levels induced carbohydrates production in A. terreus LF2. These results hint at the involvement of carbohydrates in the Cu-tolerance mechanism of the latter. Copper accumulation in both species was further demonstrated through scanning electron microscopy and energy dispersive spectrometry. In line with the pertaining literature, our results are somewhat inconclusive concerning whether proteins or carbohydrates play a more pivotal role in copper complexation in both species; yet, FTIR analysis showed the participation of different functional groups in Cu sorption. Overall, although additional research is required to advance the knowledge about both Aspergillus species, our findings suggest that A. terreus LF2 presents greater promise for copper bioremediation due to enhanced tolerance and accumulation capacity.

A Remarkable Expansion of Oligopeptide Transporter Genes in Rust Fungi (Pucciniales) Suggests a Specialization in Nutrient Acquisition for Obligate Biotrophy

Nutrient acquisition by rust fungi during their biotrophic growth has been assigned to a few transporters expressed in haustorial infection structures. We performed a comparative genomic analysis of all transporter genes (hereafter termed transportome) classified according to the Transporter Classification Database, focusing specifically on rust fungi (order Pucciniales) versus other species in the Dikarya. We also surveyed expression of transporter genes in the poplar rust fungus for which transcriptomics data are available across the whole life cycle. Despite a significant increase in gene number, rust fungi presented a reduced transportome compared with most fungi in the Dikarya. However, a few transporter families in the subclass Porters showed significant expansions. Notably, three metal transport-related families involved in the import, export, and sequestration of metals were expanded in Pucciniales and expressed at various stages of the rust life cycle, suggesting a tight regulation of metal homeostasis. The most remarkable gene expansion in the Pucciniales was observed for the oligopeptide transporter (OPT) family, with 25 genes on average compared with seven to 14 genes in the other surveyed taxonomical ranks. A phylogenetic analysis showed several specific expansion events at the root of the order Pucciniales with subsequent expansions in rust taxonomical families. The OPT genes showed dynamic expression patterns along the rust life cycle and more particularly during infection of the poplar host tree, suggesting a possible specialization for the acquisition of nitrogen and sulfur through the transport of oligopeptides from the host during biotrophic growth.

Schizosaccharomyces pombe Grx4, Fep1, and Php4: In silico analysis and expression response to different iron concentrations

Due to iron's essential role in cellular metabolism, most organisms must maintain their homeostasis. In this regard, the fission yeast Schizosaccharomyces pombe (sp) uses two transcription factors to regulate intracellular iron levels: spFep1 under iron-rich conditions and spPhp4 under iron-deficient conditions, which are controlled by spGrx4. However, bioinformatics analysis to understand the role of the spGrx4/spFep1/spPhp4 axis in maintaining iron homeostasis in S. pombe is still lacking. Our study aimed to perform bioinformatics analysis on S. pombe proteins and their sequence homologs in Aspergillus flavus (af), Saccharomyces cerevisiae (sc), and Homo sapiens (hs) to understand the role of spGrx4, spFep1, and spPhp4 in maintaining iron homeostasis. The three genes' expression patterns were also examined at various iron concentrations. A multiple sequence alignment analysis of spGrx4 and its sequence homologs revealed a conserved cysteine residue in each PF00085 domain. Blast results showed that hsGLRX3 is most similar to spGrx4. In addition, spFep1 is most closely related in sequence to scDal80, whereas scHap4 is most similar to spFep1. We also found two highly conserved motifs in spFep1 and its sequence homologs that are significant for iron transport systems because they contain residues involved in iron homeostasis. The scHap4 is most similar to spPhp4. Using STRING to analyze protein-protein interactions, we found that spGrx4 interacts strongly with spPhp4 and spFep1. Furthermore, spGrx4, spPhp4, and spFep1 interact with spPhp2, spPhp3, and spPhp5, indicating that the three proteins play cooperative roles in iron homeostasis. At the highest level of Fe, spgrx4 had the highest expression, followed by spfep1, while spphp4 had the lowest expression; a contrast occurred at the lowest level of Fe, where spgrx4 expression remained constant. Our findings support the notion that organisms develop diverse strategies to maintain iron homeostasis.

Potential of bioaugmentation of heavy metal contaminated soils in the Zambian Copperbelt using autochthonous filamentous fungi

There is great potential to remediate heavy metal contaminated environments through bioaugmentation with filamentous fungi. However, these fungi have been poorly investigated in most developing countries, such as Zambia. Therefore, the present study aimed at isolating indigenous filamentous fungi from heavy metal contaminated soil and to explore their potential for use in bioaugmentation. The conventional streak plate method was used to isolate fungi from heavy metal-contaminated soil. Filamentous fungal isolates were identified using morphological and molecular techniques. The radial growth diameter technique was used to evaluate heavy metal tolerance of the fungi. The most abundant and highly tolerant fungi, identified as Aspergillus transmontanensis, Cladosporium cladosporioides, and Geotrichum candidum species, were used to bioremediate heavy metal contaminated soil samples with uncontaminated soil sample being employed as a control. A maximum tolerance index (TI) between 0.7 and 11.0 was observed for A. transmontanensis, and G. candidum while C. cladosporioides displayed the TI between 0.2 and 1.2 in the presence of 1,000 ppm of Cu, Co, Fe, Mn, and Zn. The interspecific interaction was analyzed to determine the compatibility among isolates. Our results showed mutual intermingling between the three evaluated fungal species, which confirms their common influence in biomineralization of heavy metals in contaminated soils. Maximum bio-removal capacities after 90 days were 72% for Cu, 99.8% for Co, 60.6% for Fe, 82.2% for Mn, and 100% for both Pb and Zn. This study has demonstrated the potential of highly resistant autochthonous fungal isolates to remediate the heavy metal contamination problem.

The bianchetto truffle (Tuber borchii) a lead-resistant ectomycorrhizal fungus increases Quercus cerris phytoremediation potential

Tuber borchii is a European edible truffle which forms ectomycorrhizas with several soft- and hardwood plants. In this article, the effects of high level of Pb on the in vitro growth of five T. borchii strains and the molecular mechanisms involved in Pb tolerance were studied. Moreover, the effects of the Pb treatment on T. borchii ectomycorrhizas and on the growth, element uptake and distribution in different organs of Quercus cerris seedlings were investigated. The results showed an extraordinary tolerance of T. borchii mycelium to Pb: all the tested strains were able to grow at Pb concentration over 4000 mg L^-1 . The mechanisms of tolerance seem related to Pb sequestration in the vacuole and its immobilization as crystal of Pb oxalate outside the hyphae rather than detoxification processes, considering the low expression of glutaredoxin and thioredoxin genes. T. borchii-Q. cerris mycorrhizas tolerate a soil concentration of Pb from 1869 to 4030 mg kg^-1 although, at these Pb concentrations, T. borchii showed a reduced ability to colonize roots. T. borchii mycorrhization increased the uptake of Pb by Q. cerris. Mycorrhization and Pb treatment also significantly influenced the uptake and translocation in the plant of other elements.

Investigation the global effect of rare earth gadolinium on the budding Saccharomyces cerevisiae by genome-scale screening

Introduction

The rare earth gadolinium (Gd) is widely used in industry and medicine, which has been treated as an emerging pollutant in environment. The increasing pollution of Gd has potential hazards to living organisms. Thus it is essential to investigate the toxicity and action mechanism of Gd in biological system.

Methods

In this study, the global effect and activation mechanism of Gd on yeast were investigated by genome-scale screening.

Results and discussion

Our results show that 45 gene deletion strains are sensitive to Gd and 10 gene deletion strains are Gd resistant from the diploid gene deletion strain library of Saccharomyces cerevisiae. The result of localization analysis shows that most of these genes are involved in cell metabolism, cell cycle, transcription, translation, protein synthesis, protein folding, and cell transport. The result of functional analysis shows that four genes (CNB1, CRZ1, VCX1, and GDT1) are involved in the calcium signaling pathway, and four genes (PHO84, PHO86, PHO2, and PHO4) are involved in phosphorus metabolism. For Gd3+ has the similar ion radius with Ca2+ and easily binds to the phosphate radical, it affects Ca2+ signaling pathway and phosphorus metabolism. The genes ARF1, ARL1, ARL3, SYS1, COG5, COG6, YPT6, VPS9, SSO2, MRL1, AKL1, and TRS85 participate in vesicle transport and protein sorting. Thus, Gd accumulation affects the function of proteins related to vesicle transport, which may result in the failure of Gd transport out of cells. In addition, the intracellular Gd content in the 45 sensitive deletion strains is higher than that in the wild type yeast under Gd stress. It suggests that the sensitivity of yeast deletion strains is related to the excessive intracellular Gd accumulation.

Mycosynthesis of Metal-Containing Nanoparticles-Fungal Metal Resistance and Mechanisms of Synthesis

In the 21st century, nanomaterials play an increasingly important role in our lives with applications in many sectors, including agriculture, biomedicine, and biosensors. Over the last two decades, extensive research has been conducted to find ways to synthesise nanoparticles (NPs) via mediation with fungi or fungal extracts. Mycosynthesis can potentially be an energy-efficient, highly adjustable, environmentally benign alternative to conventional physico-chemical procedures. This review investigates the role of metal toxicity in fungi on cell growth and biochemical levels, and how their strategies of resistance, i.e., metal chelation, biomineral formation, biosorption, bioaccumulation, compartmentalisation, and efflux of metals from cells, contribute to the synthesis of metal-containing NPs used in different applications, e.g., biomedical, antimicrobial, catalytic, biosensing, and precision agriculture. The role of different synthesis conditions, including that of fungal biomolecules serving as nucleation centres or templates for NP synthesis, reducing agents, or capping agents in the synthesis process, is also discussed. The authors believe that future studies need to focus on the mechanism of NP synthesis, as well as on the influence of such conditions as pH, temperature, biomass, the concentration of the precursors, and volume of the fungal extracts on the efficiency of the mycosynthesis of NPs.

Antifungal Effect of Nanoparticles against COVID-19 Linked Black Fungus: A Perspective on Biomedical Applications

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a highly transmissible and pathogenic coronavirus that has caused a 'coronavirus disease 2019' (COVID-19) pandemic in multiple waves, which threatens human health and public safety. During this pandemic, some patients with COVID-19 acquired secondary infections, such as mucormycosis, also known as black fungus disease. Mucormycosis is a serious, acute, and deadly fungal infection caused by Mucorales-related fungal species, and it spreads rapidly. Hence, prompt diagnosis and treatment are necessary to avoid high mortality and morbidity rates. Major risk factors for this disease include uncontrolled diabetes mellitus and immunosuppression that can also facilitate increases in mucormycosis infections. The extensive use of steroids to prevent the worsening of COVID-19 can lead to black fungus infection. Generally, antifungal agents dedicated to medical applications must be biocompatible, non-toxic, easily soluble, efficient, and hypoallergenic. They should also provide long-term protection against fungal growth. COVID-19-related black fungus infection causes a severe increase in fatalities. Therefore, there is a strong need for the development of novel and efficient antimicrobial agents. Recently, nanoparticle-containing products available in the market have been used as antimicrobial agents to prevent bacterial growth, but little is known about their efficacy with respect to preventing fungal growth, especially black fungus. The present review focuses on the effect of various types of metal nanoparticles, specifically those containing silver, zinc oxide, gold, copper, titanium, magnetic, iron, and carbon, on the growth of various types of fungi. We particularly focused on how these nanoparticles can impact the growth of black fungus. We also discussed black fungus co-infection in the context of the global COVID-19 outbreak, and management and guidelines to help control COVID-19-associated black fungus infection. Finally, this review aimed to elucidate the relationship between COVID-19 and mucormycosis.

Metal nanoparticles against fungicide resistance: alternatives or partners?

Chemical control suffers from the loss of available conventional active ingredients due to strict environmental safety regulations which, combined with the loss of fungicide efficacy due to resistance development, constitute major problems of contemporary crop protection. Metal-containing nanoparticles (MNPs) appear to have all the credentials to be next-generation, eco-compatible fungicide alternatives and a valuable anti-resistance management tool. Could the introduction of MNPs as nano-fungicides be the answer to both reducing the environmental footprint of xenobiotics and dealing with fungicide resistance? The potential of MNPs to be utilized as nano-fungicides, both as alternatives to conventional fungicides or/and as partners in combating fungicide resistance, is discussed in terms of effectiveness, potential antimicrobial mechanisms as well as synergy profiles with conventional fungicides. However, their "golden" potential to be used both as alternatives and partners of conventional fungicides to combat resistance and reduce environmental pollution is challenged by undesirable effects towards non-target organisms such as phytotoxicity, toxicity to humans and environmental ecotoxicity, constituting risks that should be considered before their commercial introduction as nano-pesticides at a large scale. © 2022 Society of Chemical Industry.

Microbial silver resistance mechanisms: recent developments

In this mini-review, after a brief introduction into the widespread antimicrobial use of silver ions and nanoparticles against bacteria, fungi and viruses, the toxicity of silver compounds and the molecular mechanisms of microbial silver resistance are discussed, including recent studies on bacteria and fungi. The similarities and differences between silver ions and silver nanoparticles as antimicrobial agents are also mentioned. Regarding bacterial ionic silver resistance, the roles of the sil operon, silver cation efflux proteins, and copper-silver efflux systems are explained. The importance of bacterially produced exopolysaccharides as a physiological (biofilm) defense mechanism against silver nanoparticles is also emphasized. Regarding fungal silver resistance, the roles of metallothioneins, copper-transporting P-type ATPases and cell wall are discussed. Recent evolutionary engineering (adaptive laboratory evolution) studies are also discussed which revealed that silver resistance can evolve rapidly in bacteria and fungi. The cross-resistance observed between silver resistance and resistance to other heavy metals and antibiotics in bacteria and fungi is also explained as a clinically and environmentally important issue. The use of silver against bacterial and fungal biofilm formation is also discussed. Finally, the antiviral effects of silver and the use of silver nanoparticles against SARS-CoV-2 and other viruses are mentioned. To conclude, silver compounds are becoming increasingly important as antimicrobial agents, and their widespread use necessitates detailed understanding of microbial silver response and resistance mechanisms, as well as the ecological effects of silver compounds. Figure created with BioRender.com.

Zinc nanoparticles: Mode of action and efficacy against boscalid-resistant Alternaria alternata isolates

The antifungal potential of ZnO-NPs against Alternaria alternata isolates with reduced sensitivity to the succinate dehydrogenase inhibitor (SDHI) boscalid, resulting from target site modifications, was evaluated in vitro and in vivo. ZnO-NPs could effectively inhibit mycelial growth in a dose-dependent way in both boscalid (BOSC) sensitive (BOSC-S) and resistant (BOSC-R) isolates. The fungitoxic effect of ZnO-NPs against the pathogen was significantly enhanced when combined with boscalid compared to the individual treatments in all phenotype cases (BOSC-S/R) both in vitro and in vivo. Fungitoxic effect of ZnO-NPs could be, at least partly, attributed to zinc ion release as indicated by the positive correlation between sensitivities to the nanoparticles and their ionic counterpart ZnSO₄ and the alleviation of the ZnO-NPs fungitoxic action in the presence of the strong chelating agent EDTA. The superior effectiveness of ZnO-NPs against A. alternata, compared to ZnSO_4, could be due to nanoparticle properties interfering with cellular ion homeostasis mechanisms. The observed additive action of the oxidative phosphorylation-uncoupler fluazinam (FM) against all phenotypes indicates a possible role of ATP-dependent ion efflux mechanism in the mode of action of ZnO-NPs. A potential role of ROS production in the fungitoxic action of ZnO-NPs was evident by the additive/synergistic action of salicylhydroxamate (SHAM), which blocks the alternative oxidase antioxidant action. Mixture of ZnO-NPs and boscalid, resulting in a "capping" effect for the nanoparticles and significantly reducing their mean size, probably accounted for the synergistic effect of the mixture against both sensitive and resistant A. alternata isolates. Summarizing, results indicated that ZnO-NPs can be effectively used against A. alternata both alone or in combination with boscalid, providing an effective tool for combating SDHI-resistance and reducing the environmental fingerprint of synthetic fungicides.

Novel avenues for identification of new antifungal drugs and current challenges

INTRODUCTION

: Some of otherwise useful fungi are pathogenic to humans, and unfortunately, the number of these pathogens is increasing. In addition to common skin infections, these opportunistic pathogens are able to cause severe, often incurable, systemic mycoses.

AREAS COVERED

: The number of antifungal drugs is limited, especially drugs that can be used for systemic administration, and resistance to these drugs is very common. This review summarizes various approaches to the discovery and development of new antifungal drugs, provides an overview of the most important molecules in terms of basic (laboratory) research and compounds currently in clinical trials, and focuses on drug repurposing strategy, while providing an overview of drugs of other indications that have been tested in vitro for their antifungal activity for possible expansion of antifungal drugs and/or support of existing antimycotics.

EXPERT OPINION

: Despite the limitations of the research of new antifungal drugs by pharmaceutical manufacturers, in addition to innovated molecules based on clinically used drugs, several completely new small entities with unique mechanisms of actions have been identified. The identification of new molecular targets that offer alternatives for the development of new unique selective antifungal highly effective agents has been an important outcome of repurposing of non-antifungal drugs to antifungal drug. Also, given the advances in monoclonal antibodies and their application to immunosuppressed patients, it may seem possible to predict a more optimistic future for antifungal therapy than has been the case in recent decades.

Comparative Copper Resistance Strategies of Rhodonia placenta and Phanerochaete chrysosporium in a Copper/Azole-Treated Wood Microcosm

Copper-based formulations of wood preservatives are widely used in industry to protect wood materials from degradation caused by fungi. Wood treated with preservatives generate toxic waste that currently cannot be properly recycled. Despite copper being very efficient as an antifungal agent against most fungi, some species are able to cope with these high metal concentrations. This is the case for the brown-rot fungus Rhodonia placenta and the white-rot fungus Phanerochaete chrysosporium, which are able to grow efficiently in pine wood treated with Tanalith E3474. Here, we aimed to test the abilities of the two fungi to cope with copper in this toxic environment and to decontaminate Tanalith E-treated wood. A microcosm allowing the growth of the fungi on industrially treated pine wood was designed, and the distribution of copper between mycelium and wood was analysed within the embedded hyphae and wood particles using coupled X-ray fluorescence spectroscopy and Scanning Electron Microscopy (SEM)/Electron Dispersive Spectroscopy (EDS). The results demonstrate the copper biosorption capacities of P. chrysosporium and the production of copper-oxalate crystals by R. placenta. These data coupled to genomic analysis suggest the involvement of additional mechanisms for copper tolerance in these rot fungi that are likely related to copper transport (import, export, or vacuolar sequestration).

Intracellular sequestration of cadmium and zinc in ectomycorrhizal fungus Amanita muscaria (Agaricales, Amanitaceae) and characterization of its metallothionein gene

Amanita muscaria is an ectomycorrhizal mushroom that commonly grows at metal-polluted sites. Sporocarps from the lead smelter-polluted area near Příbram (Central Bohemia, Czech Republic) showed elevated concentrations of Cd and Zn. Size exclusion chromatography of the cell extracts of the sporocarps from both polluted and unpolluted sites indicated that substantial part of intracellular Cd and Zn was sequestered in 6-kDa complexes, presumably with metallothionein(s) (MT). When the cultured mycelial isolates were compared, those from Příbram were more Cd-tolerant and accumulated slightly less Cd and Zn than those from the unpolluted site. The analysis of the available A.muscaria sequence data returned a 67-amino acid (AA) MT encoded by the AmMT1 gene. Weak Cd and Zn responsiveness of AmMT1 in the mycelia suggested its metal homeostasis function in A.muscaria, rather than a major role in detoxification. The AmMT1 belongs to a ubiquitous peptide group in the Agaricomycetes consisting of 60-70-AA MTs containing seven cysteinyl domains and a conserved histidyl, features observed also in a newly predicted, atypical 45-AA RaMT1 of the Zn-accumulator Russula bresadolae in which the C-terminal cysteinyl domains VI and VII are missing. Heterologous expression in metal-sensitive yeast mutants indicated that AmMT1 and RaMT1 encode functional peptides that can protect cells against Cd, Zn, and Cu toxicity. The metal protection phenotype observed in yeasts with mutant variants of AmMT1 and RaMT1 further indicated that the conserved histidyl seems to play a structural, not metal binding role, and the cysteinyls of the C-terminal domains VI and VII are important for Cu binding. The data provide an important insight into the metal handling of site-associated ectomycorrhizal species disturbed by excess metals and the properties of MTs common in Agaricomycetes.

Physiological Response of Saccharomyces cerevisiae to Silver Stress

Silver nanoparticle (AgNP) production and their use as antimicrobial agents is a current area of active research. Biosynthesis is the most sustainable production method, and fungi have become candidates of interest in AgNP production. However, investigations into the physiological responses of fungi due to silver exposure are scanty. This present work utilized two strains of Saccharomyces cerevisiae (one used in commercial fermentation and a naturally occurring strain) to determine the physiological consequences of their transient exposure to AgNO₃. The assessments were based on studies involving growth curves, minimal inhibitory concentration assays, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) imaging, and inductively coupled plasma optical emission spectroscopy (ICP-OES). Results indicated (a) the capability of S. cerevisiae to produce silver nanoparticles, even at elevated levels of exposure; (b) strain origin had no significant impact on S. cerevisiae physiological response to AgNO₃; and (c) coexposure to copper and silver significantly increased intracellular copper, silver, and calcium in treated yeast cells. In addition, electron microscopy and ICP-OES results revealed that both strains internalized silver after exposure, resulting in the shrunken and distorted physical appearance visible on SEM micrographs of treated cells. Though a promising candidate for AgNPs biosynthesis, this study analyzed the effects of transient silver exposure on S. cerevisiae growth physiology and morphology.

First Report of the Biosynthesis and Characterization of Silver Nanoparticles Using Scabiosa atropurpurea subsp. maritima Fruit Extracts and Their Antioxidant, Antimicrobial and Cytotoxic Properties

Candida and dermatophyte infections are difficult to treat due to increasing antifungal drugs resistance such as fluconazole, as well as the emergence of multi-resistance in clinical bacteria. Here, we first synthesized silver nanoparticles using aqueous fruit extracts from Scabiosa atropurpurea subsp. maritima (L.). The characterization of the AgNPs by means of UV, XRD, FTIR, and TEM showed that the AgNPs had a uniform spherical shape with average sizes of 40–50 nm. The biosynthesized AgNPs showed high antioxidant activity when investigated using 1,1-diphenyl-2-picryl-hydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays. The AgNPs displayed strong antibacterial potential expressed by the maximum zone inhibition and the lowest MIC and MBC values. The AgNPs revealed a significant antifungal effect against the growth and biofilm of Candida species. In fact, the AgNPs were efficient against Trichophyton rubrum, Trichophyton interdigitale, and Microsporum canis. The antifungal mechanisms of action of the AgNPs seem to be due to the disruption of membrane integrity and a reduction in virulence factors (biofilm and hyphae formation and a reduction in germination). Finally, the silver nanoparticles also showed important cytotoxic activity against the human multiple myeloma U266 cell line and the human breast cancer cell line MDA-MB-231. Therefore, we describe new silver nanoparticles with promising biomedical application in the development of novel antimicrobial and anticancer agents.

A comprehensive assessment of Yarrowia lipolytica and its interactions with metals: Current updates and future prospective

The non-conventional yeast Yarrowia lipolytica has been popular as a model system for understanding biological processes such as dimorphism and lipid accumulation. The organism can efficiently utilize hydrophobic substrates (hydrocarbons and triglycerides) thereby rendering it relevant in bioremediation of oil polluted environments. The current review focuses on the interactions of this fungus with metal pollutants and its potential application in bioremediation of metal contaminated locales. This fungus is intrinsically equipped with a variety of physiological and biochemical features that enable it to tide over stress conditions induced by the presence of metals. Production of enzymes such as phosphatases, reductases and superoxide dismutases are worth a special mention. In the presence of metals, levels of inherently produced metal binding proteins (metallothioneins) and the pigment melanin are seen to be elevated. Morphological alterations with respect to biofilm formation and dimorphic transition from yeast to mycelial form are also induced by certain metals. The biomass of Y. lipolytica is inherently important as a biosorbent and cell surface modification, process optimization or whole cell immobilization techniques have aided in improving this capability. In the presence of metals such as mercury, cadmium, copper and uranium, the culture forms nanoparticulate deposits. In addition, on account of its intrinsic reductive ability, Y. lipolytica is being exploited for synthesizing nanoparticles of gold, silver, cadmium and selenium with applications as antimicrobial compounds, location agents for bioimaging and as feed supplements. This versatile organism thus has great potential in interacting with various metals and addressing problems related to their pollutant status.

Fungal and oomycete pathogens and heavy metals: an inglorious couple in the environment

Heavy metal (HM) contamination of the environment is a major problem worldwide. The rate of global deposition of HMs in soil has dramatically increased over the past two centuries and there of facilitated their rapid accumulation also in living systems. Although the effects of HMs on plants, animals and humans have been extensively studied, yet little is known about their effects on the (patho)biology of the microorganisms belonging to a unique group of filamentous eukaryotic pathogens, i.e., fungi and oomycetes. Much of the literature concerning mainly model species has revealed that HM stress affects their hyphal growth, morphology, and sporulation. Toxicity at cellular level leads to disturbance of redox homeostasis manifested by the formation of nitro-oxidative intermediates and to the induction of antioxidant machinery. Despite such adverse effects, published data is indicative of the fact that fungal and oomycete pathogens have a relatively high tolerance to HMs in comparison to other groups of microbes such as bacteria. Likely, these pathogens may harbor a network of detoxification mechanisms that ensure their survival in a highly HM-polluted (micro)habitat. Such a network may include extracellular HMs immobilization, biosorption to cell wall, and/or their intracellular sequestration to proteins or other ligands. HMs may also induce a hormesis-like phenomenon allowing the pathogens to maintain or even increase fitness against chemical challenges. Different scenarios linking HMs stress and modification of the microorganisms pathogenicity are disscused in this review.

Marginal lands and fungi - linking the type of soil contamination with fungal community composition

Fungi can be found in almost all ecosystems. Some of them can even survive in harsh, anthropogenically transformed environments, such as post-industrial soils. In order to verify how the soil fungal diversity may be changed by pollution, two soil samples from each of the 28 post-industrial sites were collected. Each soil sample was characterized in terms of concentration of heavy metals and petroleum derivatives. To identify soil fungal communities, fungal ITS2 amplicon was sequenced for each sample using Illumina MiSeq platform. There were significant differences in the community structure and taxonomic diversity among the analyzed samples. The highest taxon richness and evenness were observed in the non-polluted sites, and lower numbers of taxa were identified in multi-polluted soils. The presence of monocyclic aromatic hydrocarbons, gasoline, and mineral oil were determined as the factors driving the differences in the mycobiome. Further, in the culture-based selection experiment, two main groups of fungi growing on polluted media were identified - generalists able to live in the presence of pollution, and specialists adapted to the usage of BTEX as a sole source of energy. Our selection experiment proved that it is long-term soil contamination that shapes the community, rather than temporary addition of pollutant. This article is protected by copyright. All rights reserved.

Antifungal Effect of Copper Nanoparticles against Fusarium kuroshium, an Obligate Symbiont of Euwallacea kuroshio Ambrosia Beetle

Copper nanoparticles (Cu-NPs) have shown great antifungal activity against phytopathogenic fungi, making them a promising and affordable alternative to conventional fungicides. In this study, we evaluated the antifungal activity of Cu-NPs against Fusarium kuroshium, the causal agent of Fusarium dieback, and this might be the first study to do so. The Cu-NPs (at different concentrations) inhibited more than 80% of F. kuroshium growth and were even more efficient than a commercial fungicide used as a positive control (cupric hydroxide). Electron microscopy studies revealed dramatic damage caused by Cu-NPs, mainly in the hyphae surface and in the characteristic form of macroconidia. This damage was visible only 3 days post inoculation with used treatments. At a molecular level, the RNA-seq study suggested that this growth inhibition and colony morphology changes are a result of a reduced ergosterol biosynthesis caused by free cytosolic copper ions. Furthermore, transcriptional responses also revealed that the low- and high-affinity copper transporter modulation and the endosomal sorting complex required for transport (ESCRT) are only a few of the distinct detoxification mechanisms that, in its conjunction, F. kuroshium uses to counteract the toxicity caused by the reduced copper ion.

Estimation of Serum Levels of Heavy Metals in Patients with Chronic Invasive Fungal Rhinosinusitis Before the COVID-19 Era: A Pilot Study

Objective:

Various metals play role in the survival and pathogenesis of the invasive fungal disease. The objectives of this study were to compare the levels of heavy metals in patients with chronic invasive fungal rhinosinusitis (CIFR) and healthy controls, and to analyze their role in disease outcome.

Methods:

Twenty-three patients (15 with invasive mucormycosis and 8 with invasive aspergillosis, Group 1), and 14 healthy controls (Group 2) were recruited. Blood samples were collected from each group into ion-free tubes and analyzed for serum levels of Nickel (Ni), Copper (Cu), Zinc (Zn), Gallium (Ga), Arsenic (As), Selenium (Se), Rubidium (Rb), Strontium (Sr), Cadmium (Cd), and Lead (Pb). The final outcome of the patients during their hospital stay was categorized clinico-radiologically as improved or worsened, or death.

Results:

The levels of all metals were higher in Group 1 except for As and Pb. However, the differences in Cu (p=0.0026), Ga (p=0.002), Cd (p=0.0027), and Pb (p=0.0075) levels were significant. Higher levels of Zn (p=0.009), Se (p=0.020), and Rb (p=0.016) were seen in the invasive aspergillosis subgroup. Although Zn (p=0.035), As (p=0.022), and Sr (p=0.002) levels were higher in patients with improved outcome, subgroup analysis showed no differences.

Conclusion:

The levels of some heavy metals in CIFR significantly differ from those of the general population and also vary with the type of the disease and its outcome. These levels may not have a direct effect on the outcome of the patient, but they do play a role in the pathogenesis of the invading fungus.

Antibacterial, Antifungal, and Antioxidant Activities of Silver Nanoparticles Biosynthesized from Bauhinia tomentosa Linn

The biogenic synthesis of silver nanoparticles (AgNPs) has a wide range of applications in the pharmaceutical industry. Here, we synthesized AgNPs using the aqueous flower extract of Bauhinia tomentosa Linn. Formation of AgNPs was observed using ultraviolet-visible light spectrophotometry at different time intervals. Maximum absorption was observed after 4 h at 420 nm due to the reduction of Ag⁺ to Ag⁰. The stabilizing activity of functional groups was identified by Fourier-transform infrared spectroscopy. Size and surface morphology were also analyzed using scanning electron microscopy. The present study revealed the AgNPs were spherical in form with a diameter of 32 nm. The face-centered cubic structure of AgNPs was indexed using X-ray powder diffraction with peaks at 2θ = 37°, 49°, 63°, and 76° (corresponding to the planes of silver 111, 200, 220, 311), respectively. Energy-dispersive X-ray spectroscopy revealed that pure reduced silver (Ag⁰) was the major constituent (59.08%). Antimicrobial analyses showed that the biosynthesized AgNPs possess increased antibacterial activity (against Staphylococcus aureus (Gram-positive) and Escherichia coli (Gram-negative), with larger zone formation against S. aureus (9.25 mm) compared with that of E. coli (6.75 mm)) and antifungal activity (against Aspergillus flavus and Candida albican (with superior inhibition against A. flavus (zone of inhibition: 7 mm) compared with C. albicans (zone of inhibition: 5.75 mm)). Inhibition of 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity was found to be dose-dependent with half-maximal inhibitory concentration (IC₅₀) values of 56.77 μg/mL and 43.03 μg/mL for AgNPs and ascorbic acid (control), respectively, thus confirming that silver nanoparticles have greater antioxidant activity than ascorbic acid. Molecular docking was used to determine the mode of antimicrobial interaction of our biosynthesized B. tomentosa Linn flower-powder extract-derived AgNPs. The biogenic AgNPs preferred hydrophobic contacts to inhibit bacterial and fungal sustainability with reducing antioxidant properties, suggesting that biogenic AgNPs can serve as effective medicinal agents.

Copper-Containing Nanoparticles and Organic Complexes: Metal Reduction Triggers Rapid Cell Death via Oxidative Burst

Copper-containing agents are promising antitumor pharmaceuticals due to the ability of the metal ion to react with biomolecules. In the current study, we demonstrate that inorganic Cu²⁺ in the form of oxide nanoparticles (NPs) or salts, as well as Cu ions in the context of organic complexes (oxidation states +1, +1.5 and +2), acquire significant cytotoxic potency (2–3 orders of magnitude determined by IC₅₀ values) in combinations with N-acetylcysteine (NAC), cysteine, or ascorbate. In contrast, other divalent cations (Zn, Fe, Mo, and Co) evoked no cytotoxicity with these combinations. CuO NPs (0.1–1 µg/mL) together with 1 mM NAC triggered the formation of reactive oxygen species (ROS) within 2–6 h concomitantly with perturbation of the plasma membrane and caspase-independent cell death. Furthermore, NAC potently sensitized HCT116 colon carcinoma cells to Cu–organic complexes in which the metal ion coordinated with 5-(2-pyridylmethylene)-2-methylthio-imidazol-4-one or was present in the coordination sphere of the porphyrin macrocycle. The sensitization effect was detectable in a panel of mammalian tumor cell lines including the sublines with the determinants of chemotherapeutic drug resistance. The components of the combination were non-toxic if added separately. Electrochemical studies revealed that Cu cations underwent a stepwise reduction in the presence of NAC or ascorbate. This mechanism explains differential efficacy of individual Cu–organic compounds in cell sensitization depending on the availability of Cu ions for reduction. In the presence of oxygen, Cu⁺¹ complexes can generate a superoxide anion in a Fenton-like reaction Cu⁺¹L + O₂ → O₂^−. + Cu⁺²L, where L is the organic ligand. Studies on artificial lipid membranes showed that NAC interacted with negatively charged phospholipids, an effect that can facilitate the penetration of CuO NPs across the membranes. Thus, electrochemical modification of Cu ions and subsequent ROS generation, as well as direct interaction with membranes, represent the mechanisms of irreversible membrane damage and cell death in response to metal reduction in inorganic and organic Cu-containing compounds.

Regulation of Copper Metabolism by Nitrogen Utilization in Saccharomyces cerevisiae

To understand the relationship between carbon or nitrogen utilization and iron homeostasis, we performed an iron uptake assay with several deletion mutants with partial defects in carbon or nitrogen metabolism. Among them, some deletion mutants defective in carbon metabolism partially and the MEP2 deletion mutant showed lower iron uptake activity than the wild type. Mep2 is known as a high-affinity ammonia transporter in Saccharomyces cerevisiae. Interestingly, we found that nitrogen starvation resulted in lower iron uptake activity than that of wild-type cells without downregulation of the genes involved in the high-affinity iron uptake system FET3/FTR1. However, the gene expression of FRE1 and CTR1 was downregulated by nitrogen starvation. The protein level of Ctr1 was also decreased by nitrogen starvation, and addition of copper to the nitrogen starvation medium partially restored iron uptake activity. However, the expression of MAC1, which is a copper-responsive transcriptional activator, was not downregulated by nitrogen starvation at the transcriptional level but was highly downregulated at the translational level. Mac1 was downregulated dramatically under nitrogen starvation, and treatment with MG132, which is an inhibitor of proteasome-dependent protein degradation, partially attenuated the downregulation of Mac1. Taken together, these results suggest that nitrogen starvation downregulates the high-affinity iron uptake system by degrading Mac1 in a proteasome-dependent manner and eventually downregulates copper metabolism.

Physiological, Genomic and Transcriptomic Analyses Reveal the Adaptation Mechanisms of Acidiella bohemica to Extreme Acid Mine Drainage Environments

Fungi in acid mine drainage (AMD) environments are of great concern due to their potentials of decomposing organic carbon, absorbing heavy metals and reducing AMD acidity. Based on morphological analysis and ITS/18S high-throughput sequencing technology, previous studies have provided deep insights into the diversity and community composition of fungi in AMD environments. However, knowledge about physiology, metabolic potential and transcriptome profiles of fungi inhabiting AMD environments is still scarce. Here, we reported the physiological, genomic, and transcriptomic characterization of Acidiella bohemica SYSU C17045 to improve our understanding of the physiological, genomic, and transcriptomic mechanisms underlying fungal adaptation to AMD environments. A. bohemica was isolated from an AMD environment, which has been proved to be an acidophilic fungus in this study. The surface of A. bohemica cultured in AMD solutions was covered with a large number of minerals such as jarosite. We thus inferred that the A. bohemica might have the potential of biologically induced mineralization. Taking advantage of PacBio single-molecule real-time sequencing, we obtained the high-quality genome sequences of A. bohemica (50 Mbp). To our knowledge, this was the first attempt to employ a third-generation sequencing technology to explore the genomic traits of fungi isolated from AMD environments. Moreover, our transcriptomic analysis revealed that a series of genes in the A. bohemica genome were related to its metabolic pathways of C, N, S, and Fe as well as its adaptation mechanisms, including the response to acid stress and the resistance to heavy metals. Overall, our physiological, genomic, and transcriptomic data provide a foundation for understanding the metabolic potential and adaptation mechanisms of fungi in AMD environments.