The roles of zinc and copper sensing in fungal pathogenesis

The influence of a copper efflux pump in Histoplasma capsulatum virulence

During the infectious process, pathogenic microorganisms must obtain nutrients from the host in order to survive and proliferate. These nutritional sources include the metallic nutrient copper. Despite its essentiality, copper in large amounts is toxic. Host defense mechanisms use high copper poisoning as a fungicidal strategy to control infection. Transcriptional analyses showed that yeast cultured in the presence of copper or inside macrophages (24 h) had elevated expression of CRP1, a copper efflux pump, suggesting that Histoplasma capsulatum could be exposed to a high copper environment in macrophages during the innate immune stage of infection. Accordingly, macrophages cultured in high copper are more efficient in controlling H. capsulatum growth. Also, silencing of ATP7a, a copper pump that promotes the copper influx in phagosomes, increases fungal survival in macrophages. The rich copper environment faced by the fungus is not dependent on IFN-γ, since fungal CRP1 expression is induced in untreated macrophages. Appropriately, CRP1 knockdown fungal strains are more susceptible to macrophage control than wild-type yeasts. Additionally, CRP1 silencing decreases fungal burden in mice during the phase of innate immune response (4-day postinfection) and CRP1 is required for full virulence in a macrophage cell lines (J774 A.1 and RAW 264.7), as well as primary cells (BMDM). Thus, induction of fungal copper detoxifying genes during innate immunity and the attenuated virulence of CRP1-knockdown yeasts suggest that H. capsulatum is exposed to a copper-rich environment at early infection, but circumvents this condition to establish infection.

Carnosine, Zinc and Copper: A Menage a Trois in Bone and Cartilage Protection

Dysregulated metal homeostasis is associated with many pathological conditions, including arthritic diseases. Osteoarthritis and rheumatoid arthritis are the two most prevalent disorders that damage the joints and lead to cartilage and bone destruction. Recent studies show that the levels of zinc (Zn) and copper (Cu) are generally altered in the serum of arthritis patients. Therefore, metal dyshomeostasis may reflect the contribution of these trace elements to the disease's pathogenesis and manifestations, suggesting their potential for prognosis and treatment. Carnosine (Car) also emerged as a biomarker in arthritis and exerts protective and osteogenic effects in arthritic joints. Notably, its zinc(II) complex, polaprezinc, has been recently proposed as a drug-repurposing candidate for bone fracture healing. On these bases, this review article aims to provide an overview of the beneficial roles of Cu and Zn in bone and cartilage health and their potential application in tissue engineering. The effects of Car and polaprezinc in promoting cartilage and bone regeneration are also discussed. We hypothesize that polaprezinc could exchange Zn for Cu, present in the culture media, due to its higher sequestering ability towards Cu. However, future studies should unveil the potential contribution of Cu in the beneficial effects of polaprezinc.

Total transcriptome analysis of Candida auris planktonic cells exposed to tyrosol

Tyrosol, a secondary metabolite of Candida species, regulates fungal morphogenesis, and its application may represent a novel innovative therapy against emerging multi-resistant fungal superbug such as Candida auris. In the current study, the effects of tyrosol on growth, redox homeostasis, intracellular microelement contents and activities of virulence-related enzymes released by C. auris were examined. To gain further information about the effect of tyrosol exposure, we revealed gene transcriptional changes using total transcriptome sequencing (RNA-Seq). At a concentration of 15 mM, tyrosol significantly decrease the growth of fungal cells within 2 h of its addition (5.6 × 107±1.2 × 107 and 2.5 × 107±0.6 × 107 colony forming unit/mL for control and tyrosol-treated cells, respectively). Furthermore, it enhanced the release of reactive oxygen species as confirmed by a dichlorofluorescein (DCF) assay (7.3 ± 1.8 [nmol DCF (OD640)-1] versus 16.8 ± 3.9 [nmol DCF (OD640)-1]), which was coincided with elevated superoxide dismutase, catalase and glutathione peroxidase activities. Tyrosol exerted in a 37%, 25%, 34% and 55% decrease in intracellular manganese, iron, zinc and copper contents, respectively, compared to control cells. The tyrosol treatment led to a 142 and 108 differentially transcripted genes with at least a 1.5-fold increase or decrease in transcription, respectively. Genes related to iron and fatty acid metabolism as well as nucleic acid synthesis were down-regulated, whereas those related to the antioxidative defence, adhesion and oxoacid metabolic processes were up-regulated. This study shows that tyrosol significantly influences growth, intracellular physiological processes and gene transcription in C. auris, which could highly support the development of novel treatment approaches against this important pathogen.

Regulation of pseurotin A biosynthesis by GliZ and zinc in Aspergillus fumigatus

Recently, we reported that zinc regulates gliotoxin biosynthesis via ZafA, which is a zinc-responsive transcriptional activator. From an HPLC analysis of culture media of Aspergillus fumigatus, we found a trend of decreasing gliotoxin production but increasing pseurotin A and fumagillin production in proportion to the zinc concentration. The expression of the genes involved in pseurotin A biosynthesis was upregulated under high zinc concentrations. Furthermore, upregulated expression of pseurotin A biosynthetic genes and higher production of pseurotin A were observed in the zafA deletion strain. Interestingly, the deletion of gliZ, a transcriptional activator of gliotoxin biosynthesis genes, resulted in upregulated expression of pseurotin A biosynthetic genes and increased production of pseurotin A. We detected upregulation of fumR expression in the gliZ and zafA deletion mutants. The overexpression of gliZ observed in the zafA deletion mutant resulted in the failure of the mutant to increase pseurotin A production, which is a phenotype of the zafA deletion mutant. These results suggest that ZafA sequentially regulates pseurotin A biosynthesis through GliZ. Finally, we found through a murine virulence test that the gliZ and fumR double-deletion mutants showed a delayed death rate compared with the single-deletion mutants of either gliZ or fumR. Taken together, these results suggested that the biosynthesis of gliotoxin and pseurotin A are regulated in opposite ways by zinc utilization and that each secondary metabolite is synthesized when the synthesis of another secondary metabolite fails to protect it against the defense system of the host.

Transcriptome Analysis and Functional Validation Identify a Putative bZIP Transcription Factor, Fpkapc, that Regulates Development, Stress Responses, and Virulence in Fusarium pseudograminearum

Fusarium pseudograminearum is a soilborne, hemibiotrophic phytopathogenic fungus that causes Fusarium crown rot and Fusarium head blight in wheat. The basic leucine zipper proteins (bZIPs) are evolutionarily conserved transcription factors that play crucial roles in a range of growth and developmental processes and the responses to biotic and abiotic stresses. However, the roles of bZIP transcription factors remains unknown in F. pseudograminearum. In this study, a bZIP transcription factor Fpkapc was identified to localize to the nucleus in F. pseudograminearum. A mutant strain (Δfpkapc) was constructed to determine the role of Fpkapc in growth and pathogenicity of F. pseudograminearum. Transcriptomic analyses revealed that many genes involved in basic metabolism and oxidation-reduction processes were downregulated, whereas many genes involved in metal iron binding were upregulated in the Δfpkapc strain, compared with the wild type (WT). Correspondingly, the mutant had severe growth defects and displayed abnormal hyphal tips. Conidiation in the Fpkapc mutant was reduced, with more conidia in smaller size and fewer septa than in the WT. Also, relative to WT, the Δfpkapc strain showed greater tolerance to ion stress, but decreased tolerance to H₂O₂. The mutant caused smaller disease lesions on wheat and barley plants, but significantly increased TRI gene expression, compared with the WT. In summary, Fpkapc plays multiple roles in governing growth, development, stress responses, and virulence in F. pseudograminearum.

Proteome and secretome profiling of zinc availability in Cryptococcus neoformans identifies Wos2 as a subtle influencer of fungal virulence determinants

BACKGROUND

Fungal infections impact over 25% of the global population. For the opportunistic fungal pathogen, Cryptococcus neoformans, infection leads to cryptococcosis. In the presence of the host, disease is enabled by elaboration of sophisticated virulence determinants, including polysaccharide capsule, melanin, thermotolerance, and extracellular enzymes. Conversely, the host protects itself from fungal invasion by regulating and sequestering transition metals (e.g., iron, zinc, copper) important for microbial growth and survival.

RESULTS

Here, we explore the intricate relationship between zinc availability and fungal virulence via mass spectrometry-based quantitative proteomics. We observe a core proteome along with a distinct zinc-regulated protein-level signature demonstrating a shift away from transport and ion binding under zinc-replete conditions towards transcription and metal acquisition under zinc-limited conditions. In addition, we revealed a novel connection among zinc availability, thermotolerance, as well as capsule and melanin production through the detection of a Wos2 ortholog in the secretome under replete conditions.

CONCLUSIONS

Overall, we provide new biological insight into cellular remodeling at the protein level of C. neoformans under regulated zinc conditions and uncover a novel connection between zinc homeostasis and fungal virulence determinants.

The role of zinc in the pathogenicity of human fungal pathogens

Fungal pathogens now account for an unprecedented burden on human health. Like all microorganisms, these fungi must successfully forage for essential micronutrients such as zinc in order to proliferate. However, pathogenic microbes face an additional hurdle in securing zinc from their environment: the action of host nutritional immunity which strictly manipulates microbial access to this essential, but also potentially toxic trace metal. This review introduces the relevant pathogenic species and goes on to cover the molecular mechanisms of zinc uptake by human fungal pathogens. Fungi scavenge zinc from their environment via two basic mechanisms: via a family of cellular zinc importers-the ZIP transporters; and via a unique secreted zinc binding protein-the zincophore. However the genetic requirement of these systems for fungal virulence is highly species-specific. As well as zinc scarcity, potential intoxification with this heavy metal can occur and, unlike bacteria, fungi deal with environmental insult this via intraorganellar compartmentalization. Zinc availability also modulates the morphogenic behavior of a subset of pathogenic yeast species. This chapter will cover these different aspects of zinc availability on the physiology of human fungal pathogens with emphasis on the major pathogenic species Candida albicans.

Proteomic Analysis of Copper Toxicity in Human Fungal Pathogen Cryptococcus neoformans

Cryptococcus neoformans is an invasive human fungal pathogen that causes more than 181,000 deaths each year. Studies have demonstrated that pulmonary C. neoformans infection induces innate immune responses involving copper, and copper detoxification in C. neoformans improves its fitness and pathogenicity during pulmonary C. neoformans infection. However, the molecular mechanism by which copper inhibits C. neoformans proliferation is unclear. We used a metallothionein double-knockout C. neoformans mutant that was highly sensitive to copper to demonstrate that exogenous copper ions inhibit fungal cell growth by inducing reactive oxygen species generation. Using liquid chromatography-tandem mass spectrometry, we found that copper down-regulated factors involved in protein translation, but up-regulated proteins involved in ubiquitin-mediated protein degradation. We propose that the down-regulation of protein synthesis and the up-regulation of protein degradation are the main effects of copper toxicity. The ubiquitin modification of total protein and proteasome activity were promoted under copper stress, and inhibition of the proteasome pathway alleviated copper toxicity. Our proteomic analysis sheds new light on the antifungal mechanisms of copper.

Immunomodulatory diet in pediatric age

In the last few decades, the importance of a functioning immune system and health status has become more evident. Multiple factors are able to influence the development of chronic diseases and diet is one of the most important environmental factors. Evidence demonstrates that dietary patterns high in fat and low in fiber are associated with the development of non-communicable diseases. Moreover, optimal nutritional status can modulate immune maturation and response to inflammation. During inflammatory conditions, nutritional deficiencies may occur, establishing a vicious circle, consequently a balanced nutritional status is essential to prevent and counteract infections. Dietary diversity can prevent allergic diseases and nutrients such as DHA, arginine, vitamins and trace elements have an impact on physical barriers (such as gut mucosal barrier and skin), on the immune system response and on microbiome modulation. Protein deficiencies can compromise innate and adaptive immune functions; arginine availability can affect the immune response in injured states and other disease processes; EPA and DHA can modulate both innate and adaptive immunity; prebiotics have a beneficial effect on the functioning of the immune system. Zinc, copper, selenium and iron are involved in the correct development and function of the immune system. Vitamins D, E, A, B and C have a role on immune system through different mechanisms of action. Since a complex interplay exists between diet, microbiome and epigenetic factors which determine nutrient-induced changes on the immune function, the effect of each single nutrient may be difficult to study. Well-designed intervention studies, investigating the effects of whole dietary pattern, should be performed to clarify impact of foods on the immune function and disease risk.

Zrg1, a cryptococcal protein associated with regulation of growth in nutrient deprivation conditions

Cryptococcus gattii is one of the causes of cryptococcosis, a life-threatening disease generally characterized by pneumonia and/or meningitis. Zinc is an essential element for life, being required for the activity of many proteins with catalytic and structural roles. Here, we characterize ZRG1 (zinc-related gene 1), which codes a product involved in zinc metabolism. Transcriptional profiling revealed that zinc availability regulated the expression of ZRG1, and its null mutants demonstrated impaired growth in zinc- and nitrogen-limiting conditions. Moreover, zrg1 strains displayed alterations in the expression of the zinc homeostasis-related genes ZAP1 and ZIP1. Notably, cryptococcal cells lacking Zrg1 displayed upregulation of autophagy-like phenotypes. Despite no differences were detected in the classical virulence-associated traits; cryptococcal cells lacking ZRG1 displayed decreased capacity for survival inside macrophages and attenuated virulence in an invertebrate model. Together, these results indicate that ZRG1 plays an important role in proper zinc metabolism, and is necessary for cryptococcal fitness and virulence.

Copper(II) and Zinc(II) Complexes with the Clinically Used Fluconazole: Comparison of Antifungal Activity and Therapeutic Potential

Copper(II) and zinc(II) complexes with clinically used antifungal drug fluconazole (fcz), {[CuCl2(fcz)2].5H2O}n, 1, and {[ZnCl2(fcz)2]·2C2H5OH}n, 2, were prepared and characterized by spectroscopic and crystallographic methods. The polymeric structure of the complexes comprises four fluconazole molecules monodentately coordinated via the triazole nitrogen and two chlorido ligands. With respect to fluconazole, complex 2 showed significantly higher antifungal activity against Candida krusei and Candida parapsilosis. All tested compounds reduced the total amount of ergosterol at subinhibitory concentrations, indicating that the mode of activity of fluconazole was retained within the complexes, which was corroborated via molecular docking with cytochrome P450 sterol 14α-demethylase (CYP51) as a target. Electrostatic, steric and internal energy interactions between the complexes and enzyme showed that 2 has higher binding potency to this target. Both complexes showed strong inhibition of C. albicans filamentation and biofilm formation at subinhibitory concentrations, with 2 being able to reduce the adherence of C. albicans to A549 cells in vitro. Complex 2 was able to reduce pyocyanin production in Pseudomonas aeruginosa between 10% and 25% and to inhibit its biofilm formation by 20% in comparison to the untreated control. These results suggest that complex 2 may be further examined in the mixed Candida-P. aeruginosa infections.

Copper Tolerance Mediated by FgAceA and FgCrpA in Fusarium graminearum

All organisms must secure essential trace elements (e.g., Cu) for survival and reproduction. However, excess trace element accumulation in cells is highly toxic. The maintenance of copper (Cu) homeostasis has been extensively studied in mammals, bacteria, and yeast but not in plant pathogens. In this study, we investigated the molecular mechanisms of copper tolerance in Fusarium graminearum, the important wheat head scab fungus. RNA-seq revealed induced expression of the P-type ATPase transporter FgCrpA and metallothionein (MT) FgCrdA after excess Cu treatment. Deletion of FgCrpA but not FgCrdA resulted in reduced tolerance to Cu toxicity. The “Cu fist” transcription factor FgAceA was involved in Cu detoxification through activation of FgCrpA. △FgAceA was more sensitive to copper toxicity than △FgCrpA and overexpression of FgCrpA restored copper tolerance in △FgAceA. FgAceA negatively regulated aurofusarin production and its biosynthetic gene expression. △FgCrpA and △FgAceA were reduced in virulence in flowering wheat heads and synthesized decreased amounts of the mycotoxin deoxynivalenol when challenged with excess Cu. Taken together, these results suggest that mediation of Cu tolerance in F. graminearum mainly relies on the Cu efflux pump and that FgAceA governs Cu detoxification through activation of FgCrpA.

Candida albicans reprioritizes metal handling during fluconazole stress

Maintenance of metal homeostasis is critical to cell survival due to the multitude of cellular processes that depend on one or more metal cofactors. Here, we show that the opportunistic fungal pathogen Candida albicans extensively remodels its metal homeostasis networks to respond to treatment with the antifungal drug fluconazole. Disruption of the ergosterol biosynthetic pathway by fluconazole requires C. albicans adaptation, including increased Cu import and storage, increased retention of Fe, Mn, and Zn, altered utilization of Cu- and Mn-dependent enzymes, mobilization of Fe stores, and increased production of the heme prosthetic group utilized by the enzyme target of fluconazole. The findings offer a new perspective for thinking about fungal response to drug stress that pushes cells out of their metal homeostatic zones, leading them to enact metal-associated adaptation mechanisms to restore homeostasis to survive.

Candida and Candidiasis-Opportunism Versus Pathogenicity: A Review of the Virulence Traits

One of the most important questions in microbiology nowadays, is how apparently harmless, commensal yeasts like Candida spp. can cause a rising number of infections. The occurrence of the disease requires firstly the attachment to the host cells, followed by the invasion of the tissue. The adaptability translates into a rapid ability to respond to stress factors, to take up nutrients or to multiply under different conditions. By forming complex intracellular networks such as biofilms, Candida spp. become not only more refractive to antifungal therapies but also more prone to cause disease. The inter-microbial interactions can enhance the virulence of a strain. In vivo, the fungal cells face a multitude of challenges and, as a result, they develop complex strategies serving one ultimate goal: survival. This review presents the virulence factors of the most important Candida spp., contributing to a better understanding of the onset of candidiasis and raising awareness of the highly complex interspecies interactions that can change the outcome of the disease.

Type I Interferons Ameliorate Zinc Intoxication of Candida glabrata by Macrophages and Promote Fungal Immune Evasion

Host and fungal pathogens compete for metal ion acquisition during infectious processes, but molecular mechanisms remain largely unknown. Here, we show that type I interferons (IFNs-I) dysregulate zinc homeostasis in macrophages, which employ metallothionein-mediated zinc intoxication of pathogens as fungicidal response. However, Candida glabrata can escape immune surveillance by sequestering zinc into vacuoles. Interestingly, zinc-loading is inhibited by IFNs-I, because a Janus kinase 1 (JAK1)-dependent suppression of zinc homeostasis affects zinc distribution in macrophages as well as generation of reactive oxygen species (ROS). In addition, systemic fungal infections elicit IFN-I responses that suppress splenic zinc homeostasis, thereby altering macrophage zinc pools that otherwise exert fungicidal actions. Thus, IFN-I signaling inadvertently increases fungal fitness both in vitro and in vivo during fungal infections. Our data reveal an as yet unrecognized role for zinc intoxication in antifungal immunity and suggest that interfering with host zinc homeostasis may offer therapeutic options to treat invasive fungal infections.

Transcriptome Analysis Uncovers a Link Between Copper Metabolism, and Both Fungal Fitness and Antifungal Sensitivity in the Opportunistic Yeast Candida albicans

Copper homeostasis is an important determinant for virulence of many human pathogenic fungi such as the highly prevalent yeast Candida albicans. However, beyond the copper transporter Ctr1, little is known regarding other genes and biological processes that are affected by copper. To gain insight into the cellular processes that are modulated by copper abundance in C. albicans, we monitored the global gene expression dynamic under both copper depletion and excess using RNA-seq. Beyond copper metabolism, other different transcriptional programs related to fungal fitness such as stress responses, antifungal sensitivity, host invasion and commensalism were modulated in response to copper variations. We have also investigated the transcriptome of the mutant of the copper utilization regulator, mac1, and identified potential direct targets of this transcription factor under copper starvation. We also showed that Mac1 was required for the invasion and adhesion to host cells and antifungal tolerance. This study provides a framework for future studies to examine the link between copper metabolism and essential functions that modulate fungal virulence and fitness inside the host.

Zinc(II) complexes with aromatic nitrogen-containing heterocycles as antifungal agents: Synergistic activity with clinically used drug nystatin

Three novel Zn(II) complexes, [ZnCl₂(qz)₂] (1), [ZnCl₂(1,5-naph)]_n (2) and [ZnCl₂(4,7-phen)₂] (3), where qz is quinazoline, 1,5-naph is 1,5-naphthyridine and 4,7-phen is 4,7-phenanthroline, were synthesized by the reactions of ZnCl₂ and the corresponding N-heterocyclic ligand in 1:2 molar ratio in ethanol at ambient temperature. The characterization of these complexes was done by NMR, IR and UV-Vis spectroscopy, and their crystal structures were determined by single-crystal X-ray diffraction analysis. Complexes 1 and 3 are mononuclear species, in which Zn(II) ion is tetrahedrally coordinated by two nitrogen atoms belonging to two qz or 4,7-phen ligands, respectively, and by two chloride anions, while complex 2 is a 1D coordination polymer that contains 1,5-naph as bridging ligand between two metal ions. In agar disc-diffusion assay, complexes 1-3 manifested good inhibitory activity against two investigated Candida strains (C. albicans and C. parapsilosis), while not inducing toxic effects on the healthy human fibroblast cell line (MRC-5). This activity was not fungicidal, as revealed by the broth microdilution assay, however complex 3 showed the ability to modulate Candida hyphae formation, which is an important process during infection and showed significant synergistic effect with clinically used antifungal polyene nystatin.

Adapting to survive: How Candida overcomes host-imposed constraints during human colonization

Successful human colonizers such as Candida pathogens have evolved distinct strategies to survive and proliferate within the human host. These include sophisticated mechanisms to evade immune surveillance and adapt to constantly changing host microenvironments where nutrient limitation, pH fluctuations, oxygen deprivation, changes in temperature, or exposure to oxidative, nitrosative, and cationic stresses may occur. Here, we review the current knowledge and recent findings highlighting the remarkable ability of medically important Candida species to overcome a broad range of host-imposed constraints and how this directly affects their physiology and pathogenicity. We also consider the impact of these adaptation mechanisms on immune recognition, biofilm formation, and antifungal drug resistance, as these pathogens often exploit specific host constraints to establish a successful infection. Recent studies of adaptive responses to physiological niches have improved our understanding of the mechanisms established by fungal pathogens to evade the immune system and colonize the host, which may facilitate the design of innovative diagnostic tests and therapeutic approaches for Candida infections.

Common trace metals in rheumatoid arthritis: A systematic review and meta-analysis

INTRODUCTION

Environmental risk factors regrading rheumatoid arthritis (RA) have not been explored extensively. Selenium (Se), zinc (Zn) and copper (Cu) nutrients were reported to associate with RA, but the results were inconsistent. Therefore, we conduct present study to meta-analyze the relationship between serum Se, Zn and Cu and RA and review the potential mechanisms.

METHODS

PubMed, Web of Science and Cochrane Library were comprehensively searched till October 1, 2018 for pertinent studies. Standard mean differences (SMDs) and 95% confident intervals (CIs) were calculated according to random effects model.

RESULTS

Finally 41 literatures were included. Meta-analysis of 16 studies involving 806 RA patients and 959 health controls showed that serum Se (SMD = -1.04, 95% CI = -1.58 to -0.50) was decreased in RA patients, and 23 literatures with 1398 patients and 1299 controls reported serum Zn (SMD = -1.20, 95% CI = -1.74 to -0.67) was decreased. But serum Cu (SMD = 1.26, 95% CI = 0.63 to -1.89) was increased with 26 studies including 1723 patients and 1451 controls. Meta-regression reported that steroid use was positively related to serum level of Se in RA (β = 0.041, 95% CI = 0.002 to 0.079). Differences in serum Se, Zn and Cu between rheumatoid arthritis patients and controls were all related with the geographical distribution.

CONCLUSIONS

Patients with RA have significant decreased serum Se and Zn and increased serum Cu than health controls, suggesting potential roles of Se, Zn and Cu in the pathogenesis of RA. Patients and rheumatologist should give enough attention to the monitor of these elements during follow up.

Spliceosomal Prp8 intein at the crossroads of protein and RNA splicing

The spliceosome is a large ribonucleoprotein complex that removes introns from pre-mRNAs. At its functional core lies the essential pre-mRNA processing factor 8 (Prp8) protein. Across diverse eukaryotes, this protein cofactor of RNA catalysis harbors a self-splicing element called an intein. Inteins in Prp8 are extremely pervasive and are found at 7 different sites in various species. Here, we focus on the Prp8 intein from Cryptococcus neoformans (Cne), a human fungal pathogen. We solved the crystal structure of this intein, revealing structural homology among protein splicing sequences in eukaryotes, including the Hedgehog C terminus. Working with the Cne Prp8 intein in a reporter assay, we find that the biologically relevant divalent metals copper and zinc inhibit intein splicing, albeit by 2 different mechanisms. Copper likely stimulates reversible modifications on a catalytically important cysteine, whereas zinc binds at the terminal asparagine and the same critical cysteine. Importantly, we also show that copper treatment inhibits Prp8 protein splicing in Cne. Lastly, an intein-containing Prp8 precursor model is presented, suggesting that metal-induced protein splicing inhibition would disturb function of both Prp8 and the spliceosome. These results indicate that Prp8 protein splicing can be modulated, with potential functional implications for the spliceosome.

New insights into copper homeostasis in filamentous fungi

Copper is a metal ion that is required as a micronutrient for growth and proliferation. However, copper accumulation generates toxicity by multiple mechanisms, potentially leading to cell death. Due to its toxic nature at high concentrations, different chemical variants of copper have been extensively used as antifungal agents in agriculture and medicine. Most studies on copper homeostasis have been carried out in bacteria, yeast, and mammalian organisms. However, knowledge on filamentous fungi is less well documented. This review summarizes the knowledge gathered in the last few years about copper homeostasis in the filamentous fungi Aspergillus fumigatus and Aspergillus nidulans: The mechanism of action of copper, the uptake and detoxification systems, their regulation at the transcriptional level, and the role of copper homeostasis in fungal pathogenicity are presented.

Pseudomonas aeruginosa inhibits Rhizopus microsporus germination through sequestration of free environmental iron

Rhizopus spp are the most common etiological agents of mucormycosis, causing over 90% mortality in disseminated infection. Key to pathogenesis is the ability of fungal spores to swell, germinate, and penetrate surrounding tissues. Antibiotic treatment in at-risk patients increases the probability of the patient developing mucormycosis, suggesting that bacteria have the potential to control the growth of the fungus. However, research into polymicrobial relationships involving Rhizopus spp has not been extensively explored. Here we show that co-culturing Rhizopus microsporus and Pseudomonas aeruginosa results in the inhibition of spore germination. This inhibition was mediated via the secretion of bacterial siderophores, which induced iron stress on the fungus. Addition of P. aeruginosa siderophores to R. microsporus spores in the zebrafish larval model of infection resulted in inhibition of fungal germination and reduced host mortality. Therefore, during infection antibacterial treatment may relieve bacterial imposed nutrient restriction resulting in secondary fungal infections.

Molecular Characteristics of the Conserved Aspergillus nidulans Transcription Factor Mac1 and Its Functions in Response to Copper Starvation

Copper is an essential cofactor of enzymes during a variety of biochemical processes. Therefore, Cu acquisition plays critical roles in cell survival and proliferation, especially during Cu starvation. Knowledge of the key motif(s) by which the low-Cu-responsive transcription factor Mac1 senses Cu is important for understanding how Cu uptake is controlled. Findings in this study demonstrated that the Cu fist motif, but not Cys-rich motifs, is essential for Mac1-mediated Cu uptake in Aspergillus. In addition, Cu transporters CtrA2 and CtrC are both required for Mac1-mediated Cu uptake during Cu starvation in A. nidulans, indicating that species-specific machinery exists for Cu acquisition in Aspergillus.

Copper (Cu) is an essential trace element in all organisms, and Cu acquisition during periods of starvation is important for cell survival and proliferation. Although the Cu starvation-responsive transcription factor Mac1 as well as its targeted Cu transporters have been identified in Aspergillus fumigatus, the molecular mechanisms of Mac1-mediated Cu acquisition have not yet been investigated in Aspergillus. We demonstrated that Mac1 and its regulated Cu transporters are required for growth and conidiophore development during Cu starvation in Aspergillus nidulans. Moreover, A. nidulans Mac1 (AnMac1) showed highly functional conservation with the A. fumigatus homolog but not with homologs in Saccharomyces cerevisiae and Schizosaccharomyces pombe. Molecular characterization of Mac1 in A. nidulans demonstrated that the “Cu fist” motif (i.e., residues 1 through 40) harboring Cys, RGHR, and GRP residues is required for the Mac1-mediated low-Cu response but not the Cys-rich motifs REP-I and REP-II. Notably, overexpression of either the CtrA2 Cu transporter or the CtrC Cu transporter individually was unable to functionally rescue the defects in the AnMac1 deletion strain, implying that Cu uptake might require both CtrA2 and CtrC during Cu starvation, which is different from results seen with A. fumigatus. Findings in this study further suggest that the conserved Mac1-mediated Cu uptake machinery in A. fumigatus and A. nidulans is also species specific.

IMPORTANCE Copper is an essential cofactor of enzymes during a variety of biochemical processes. Therefore, Cu acquisition plays critical roles in cell survival and proliferation, especially during Cu starvation. Knowledge of the key motif(s) by which the low-Cu-responsive transcription factor Mac1 senses Cu is important for understanding how Cu uptake is controlled. Findings in this study demonstrated that the Cu fist motif, but not Cys-rich motifs, is essential for Mac1-mediated Cu uptake in Aspergillus. In addition, Cu transporters CtrA2 and CtrC are both required for Mac1-mediated Cu uptake during Cu starvation in A. nidulans, indicating that species-specific machinery exists for Cu acquisition in Aspergillus.

Thermodynamic and spectroscopic study of Cu(ii) and Zn(ii) complexes with the (148–156) peptide fragment of C4YJH2, a putative metal transporter of Candida albicans

The linker sequence between the two main Cu(ii) and Zn(ii) coordination sites of C4YJH2, a putative metal transporter of Candida albicans, contributes in a non-negligible way to the protein chelating capability.

Vitamin Biosynthesis as an Antifungal Target

The large increase in the population of immunosuppressed patients, coupled with the limited efficacy of existing antifungals and rising resistance toward them, have dramatically highlighted the need to develop novel drugs for the treatment of invasive fungal infections. An attractive possibility is the identification of possible drug targets within essential fungal metabolic pathways not shared with humans. Here, we review the vitamin biosynthetic pathways (vitamins A⁻E, K) as candidates for the development of antifungals. We present a set of ranking criteria that identify the vitamin B2 (riboflavin), B5 (pantothenic acid), and B9 (folate) biosynthesis pathways as being particularly rich in new antifungal targets. We propose that recent scientific advances in the fields of drug design and fungal genomics have developed sufficiently to merit a renewed look at these pathways as promising sources for the development of novel classes of antifungals.

For Cryptococcus neoformans, responding to the copper status in a colonization niche is not just about copper

Most fungi express two transcription factors that regulate the expression of genes associated with copper uptake for nutritional needs, and with copper resistance when copper approaches a cytotoxic level. These factors are characterized by cysteine-rich motifs which are associated with copper-sensing, DNA-binding and release, and/or cytoplasmic retention. Cryptococcus neoformans differs from most in that it expresses a single such copper-sensing trans-factor, Cuf1, a protein that up-regulates copper uptake when copper is scarce, and up-regulates copper sequestration when cells become super-replete. For C. neoformans this is an essential task in as much as copper is relatively bioavailable in lung airways while the brain interstitium can be copper-limiting for growth. While fungal dependence on and sensitivity to copper have long been considered targets for anti-fungal chemistry, fungi have proven adept at finding 'work arounds' by using a chelated form of copper as nutrient or adapting to a copper-surfaced hospital bed by increased resistance. However, the cohort of Cuf1 targets identified in this report represent far more than just the uptake and sequestration machinery, but include additional loci that, perhaps, are less easily 'defended' by the fungus. Garcia-Santamarina et al. provide that list and thus lay the ground-work for developing novel anti-fungal reagents.

Cyclic AMP Pathway Activation and Extracellular Zinc Induce Rapid Intracellular Zinc Mobilization in Candida albicans

Zinc is an essential micronutrient, required for a range of zinc-dependent enzymes and transcription factors. In mammalian cells, zinc serves as a second messenger molecule. However, a role for zinc in signaling has not yet been established in the fungal kingdom. Here, we used the intracellular zinc reporter, zinbo-5, which allowed visualization of zinc in the endoplasmic reticulum and other components of the internal membrane system in Candida albicans. We provide evidence for a link between cyclic AMP/PKA- and zinc-signaling in this major human fungal pathogen. Glucose stimulation, which triggers a cyclic AMP spike in this fungus resulted in rapid intracellular zinc mobilization and this “zinc flux” could be stimulated with phosphodiesterase inhibitors and blocked via inhibition of adenylate cyclase or PKA. A similar mobilization of intracellular zinc was generated by stimulation of cells with extracellular zinc and this effect could be reversed with the chelator EDTA. However, zinc-induced zinc flux was found to be cyclic AMP independent. In summary, we show that activation of the cyclic AMP/PKA pathway triggers intracellular zinc mobilization in a fungus. To our knowledge, this is the first described link between cyclic AMP signaling and zinc homeostasis in a human fungal pathogen.

Oxidative responses and fungal infection biology

The balance between reactive oxygen species and reactive nitrogen species production by the host and stress response by fungi is a key axis of the host-pathogen interaction. This review will describe emerging themes in fungal pathogenesis underpinning this axis.

Candida-Epithelial Interactions

A plethora of intricate and dynamic molecular interactions occur between microbes and the epithelial cells that form the mucosal surfaces of the human body. Fungi, particularly species of Candida, are commensal members of our microbiota, continuously interacting with epithelial cells. Transient and localised perturbations to the mucosal environment can facilitate the overgrowth of fungi, causing infection. This minireview will examine the direct and indirect mechanisms by which Candida species and epithelial cells interact with each other, and explore the factors involved in the central processes of adhesion, invasion, and destruction of host mucosal surfaces.

Investigation on the metal binding sites of a putative Zn(ii) transporter in opportunistic yeast species Candida albicans

The protein fragment C4YJH2 of Candida albicans has the ability to tightly coordinate Zn(ii) at its C-terminal region by means of an evolutionarily well-conserved histidine-rich sequence.

Metal-homeostasis in the pathobiology of the opportunistic human fungal pathogen Aspergillus fumigatus

In contrast to obligate pathogens opportunistic pathogens such as Aspergillus fumigatus do not need a specific host to propagate or survive. However several characteristics of the saprophytic life-style and the selective pressure encountered in the primary ecological niche contribute to the virulence of A. fumigatus. All fungi depend on metals for growth and proliferation, like iron, copper, zinc, manganese or calcium. In the recent past several studies explored the manifold impact of metals modulating virulence of pathogens. Components which might be scarce in the natural environment but also in the host due to nutritional immunity. This review recapitulates molecular constituents of metal ion uptake systems in A. fumigatus, their regulation and their significance at the host-pathogen battlefield.

Spore Germination of Pathogenic Filamentous Fungi

Fungi, algae, plants, protozoa, and bacteria are all known to form spores, especially hardy and ubiquitous propagation structures that are also often the infectious agents of diseases. Spores can survive for thousands of years, frozen in the permafrost (Kochkina et al., 2012), with the oldest viable spores extracted after 250 million years from salt crystals (Vreeland, Rosenzweig, & Powers, 2000). Their resistance to high levels of UV, desiccation, pressure, heat, and cold enables the survival of spores in the harshest conditions (Setlow, 2016). For example, Bacillus subtilis spores can survive and remain viable after experiencing conditions similar to those on Mars (Horneck et al., 2012). Spores are disseminated through environmental factors. Wind, water, or animal carriage allow spores to be spread ubiquitously throughout the environment. Spores will break dormancy and begin to germinate once exposed to favorable conditions. Germination is the mechanism that converts the spore from a dormant biological organism to one that grows vegetatively and is capable of either sexual or asexual reproduction. The process of germination has been well studied in plants, moss, bacteria, and many fungi (Hohe & Reski, 2005; Huang & Hull, 2017; Vesty et al., 2016). Unfortunately, information on the complex signaling involved in the regulation of germination, particularly in fungi remains lacking. This chapter will discuss germination of fungal spores covering our current understanding of the regulation, signaling, outcomes, and implications of germination of pathogenic fungal spores. Owing to the morphological similarities between the spore-hyphal and yeast-hyphal transition and their relevance for disease progression, relevant aspects of fungal dimorphism will be discussed alongside spore germination in this chapter.

Transcriptome sequencing and analysis of zinc-uptake-related genes in Trichophyton mentagrophytes

Background

Trichophyton mentagrophytes is an important zoonotic dermatophytic (ringworm) pathogen; causing severe skin infection in humans and other animals worldwide. Fortunately, commonly used fungal skin disease prevention and treatment measures are relatively simple. However, T. mentagrophytes is primarily studied at the epidemiology and drug efficacy research levels, yet current study has been unable to meet the needs of clinical medicine.

Zinc is a crucial trace element for the growth and reproduction of fungi and other microorganisms. The metal ions coordinate within a variety of proteins to form zinc finger proteins, which perform many vital biological functions. Zinc transport regulatory networks have not been resolved in T. mentagrophytes. The T. mentagrophytes transcriptome will allow us to discover new genes, particularly those genes involved in zinc uptake.

Result

We found T. mentagrophytes growth to be restricted by zinc deficiency; natural T. mentagrophytes growth requires zinc ions. T. Mentagrophytes must acquire zinc ions for growth and development.

The transcriptome of T. mentagrophytes was sequenced by using Illumina HiSeq™ 2000 technology and the de novo assembly of the transcriptome was performed by using the Trinity method, and functional annotation was analyzed. We got 10,751 unigenes. The growth of T. mentagrophytes is severely inhibited and there were many genes showing significant up regulation and down regulation respectively in T. mentagrophytes when zinc deficiency. Zinc deficiency can affect the expression of multiple genes of T. mentagrophytes. The effect of the zinc deficiency could be recovered in the normal medium. And we finally found the zinc-responsive activating factor (ZafA) and speculated that 4 unigenes are zinc transporters. We knocked ZafA gene by ATMT transformation in T. mentagrophytes, the result showed that ZafA gene is very important for the growth and the generation of conidia in T. mentagrophytes. The expression of 4 zinc transporter genes is potentially regulated by the zinc-responsive activating factor. The data of this study is also sufficient to be used as a support to study T. mentagrophytes.

Conclusion

We reported the first large transcriptome study carried out in T. mentagrophytes where we have compared physiological and transcriptional responses to zinc deficiency, and analyzed the expression of genes involved in zinc uptake. The study also produced high-resolution digital profiles of global genes expression relating to T. mentagrophytes growth.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4284-3) contains supplementary material, which is available to authorized users.

The cause and effect of Cryptococcus interactions with the host

Upon Cryptococcus neoformans infection of the host lung, the fungus enters a nutrient poor environment and must adapt to a variety of host-specific stress conditions (temperature, nutrient limitation, pH, CO₂). Fungal spores enter this milieu with limited nutritional reserves, germinate, and begin proliferating by budding as yeast. Although relatively little is known about the initial stages of infection, recent work has characterized changes that occur upon germination. This program and subsequent yeast-phase proliferation progress in a dynamic environment as host nutrient immunity responds to the infection via toxic accumulation or sequestration of essential micronutrients and innate immune cells are recruited to the site of infection. Adaptation to the host environment and evasion of the immune response through pathogenicity factor expression allows proliferation and dissemination to multiple sites throughout the body, including, most significantly for human disease, the central nervous system. Here we will discuss recent insights into mechanisms underlying C. neoformans interactions with the host during infection.

Zinc Limitation Induces a Hyper-Adherent Goliath Phenotype in Candida albicans

Pathogenic microorganisms often face acute micronutrient limitation during infection due to the action of host-mediated nutritional immunity. The human fungal pathogen Candida albicans is polymorphic and its morphological plasticity is one of its most widely recognized pathogenicity attributes. Here we investigated the effect of zinc, iron, manganese, and copper limitation on C. albicans morphology. Restriction of zinc specifically resulted in the formation of enlarged, spherical yeasts, a phenotype which we term Goliath cells. This cellular response to zinc restriction was conserved in C. albicans, C. dubliniensis and C. tropicalis, but not in C. parapsilosis, C. lusitaniae or Debaryomyces hansenii, suggesting that it may have emerged in the last common ancestor of these related pathogenic species. Cell wall analysis revealed proportionally more chitin exposure on the Goliath cell surface. Importantly, these cells were hyper-adherent, suggesting a possible role in pathogenicity. Interestingly, the zincophore-encoding gene PRA1 was expressed by Goliath cells in zinc limited media and lack of Pra1 inhibited both cellular enlargement and adhesion. Goliath cells represent a further layer of Candida phenotypic plasticity.

Modulation of Zinc Homeostasis in Acanthamoeba castellanii as a Possible Antifungal Strategy against Cryptococcus gattii

Cryptococcus gattii is a basidiomycetous yeast that can be found in the environment and is one of the agents of cryptococcosis, a life-threatening disease. During its life cycle, cryptococcal cells take hold inside environmental predators such as amoebae. Despite their evolutionary distance, macrophages and amoebae share conserved similar steps of phagocytosis and microbial killing. To evaluate whether amoebae also share other antifungal strategies developed by macrophages, we investigated nutritional immunity against cryptococcal cells. We focused on zinc homeostasis modulation in Acanthamoeba castellanii infected with C. gattii. The intracellular proliferation rate (IPR) in amoebae was determined using C. gattii R265 and mutants for the ZIP1 gene, which displays defects of growth in zinc-limiting conditions. We detected a reduced IPR in cells lacking the ZIP1 gene compared to wild-type strains, suggesting that amoebae produce a low zinc environment to engulfed cells. Furthermore, flow cytometry analysis employing the zinc probe Zinpyr-1 confirmed the reduced concentration of zinc in cryptococcal-infected amoebae. qRT-PCR analysis of zinc transporter-coding genes suggests that zinc export by members of the ZnT family would be involved in the reduced intracellular zinc concentration. These results indicate that amoebae may use nutritional immunity to reduce fungal cell proliferation by reducing zinc availability for the pathogen.

Cu-sensing transcription factor Mac1 coordinates with the Ctr transporter family to regulate Cu acquisition and virulence in Aspergillus fumigatus

Copper (Cu) is an essential trace element and is regarded as an important virulence factor in fungal pathogens. Previous studies suggest that a putative Cu-sensing transcription factor Mac1 and the Cu transporter Ctr family play important roles during fungal development and virulence. However, how Cu importers of the Ctr family are involved in the Cu acquisition and what is the functional relationship between them have not been fully investigated yet. Here, we demonstrate that the yeast Mac1 homolog in the opportunistic human pathogen Aspergillus fumigatus is required during colony development under low Cu conditions. Transcriptional profiling combined with LacZ reporter analyses indicate that Cu transporters ctrA2 and ctrC are expressed in an Afmac1-dependent manner upon Cu starvation, and over-expression of ctrA2 or ctrC transporters almost completely rescue the Afmac1-deletion defects, suggesting a redundancy of both transporters in Afmac1-mediated Cu uptake. Genetic analysis showed that ctrC may play a dominant role against Cu starvation relative to ctrA2 and elevated expression of ctrA2 can compensate for ctrC deletion under Cu starvation. Interestingly, both ctrA2 and ctrC deletions can suppress ctrB deletion colony defects. Our findings suggest that Ctr family proteins might coordinately regulate their functions to adapt to different Cu environments. Compared to yeast homologs, Cu family proteins in A. fumigatus may have their own working styles. Most importantly, the Afmac1 deletion strain shows a significantly attenuated pathogenicity in the neutropenic immunocompromised (a combination of cyclophosphamide and hydrocortisone) mice model, demonstrating that Afmac1 is required for pathogenesis in vivo.

A Mini HIP HOP Assay Uncovers a Central Role for Copper and Zinc in the Antifungal Mode of Action of Allicin

Garlic contains the organosulfur compound allicin which exhibits potent antifungal activity. Here we demonstrate the use of a highly simplified yeast chemical genetic screen to characterize its mode of action. By screening 24 validated yeast gene deletion "signature" strains for which hypersensitivity is characteristic for common antifungal modes of action, yeast lacking the high affinity Cu²⁺ transporter Ctr1 was found to be hypersensitive to allicin. Focusing on transition metal related genes identified two more hypersensitive strains lacking the Cu²⁺ and Zn²⁺ transcription factors Mac1 and Zap1. Hypersensitivity in these strains was reversed by the addition of Cu²⁺ and Zn²⁺ ions, respectively. The results suggest the antifungal activity of allicin is mediated through restricted Cu²⁺ and Zn²⁺ uptake or inhibition of Cu²⁺ and Zn²⁺ metalloproteins. As certain antimicrobial modes of action are much more common than others, the approach taken here provides a useful way to identify them early on.

sRNAs as possible regulators of retrotransposon activity in Cryptococcus gattii VGII

Background

The absence of Argonaute genes in the fungal pathogen Cryptococcus gattii R265 and other VGII strains indicates that yeasts of this genotype cannot have a functional RNAi pathway, an evolutionarily conserved gene silencing mechanism performed by small RNAs. The success of the R265 strain as a pathogen that caused the Pacific Northwest and Vancouver Island outbreaks may imply that RNAi machinery loss could be beneficial under certain circumstances during evolution. As a result, a hypermutant phenotype would be created with high rates of genome retrotransposition, for instance. This study therefore aimed to evaluate in silicio the effect of retrotransposons and their control mechanisms by small RNAs on genomic stability and synteny loss of C. gattii R265 through retrotransposons sequence comparison and orthology analysis with other 16 C. gattii genomic sequences available.

Results

Retrotransposon mining identified a higher sequence count to VGI genotype compared to VGII, VGIII, and VGIV. However, despite the lower retrotransposon number, VGII exhibited increased synteny loss and genome rearrangement events. RNA-Seq analysis indicated highly expressed retrotransposons as well as sRNA production.

Conclusions

Genome rearrangement and synteny loss may suggest a greater retrotransposon mobilization caused by RNAi pathway absence, but the effective presence of sRNAs that matches retrotransposon sequences means that an alternative retrotransposon silencing mechanism could be active in genomic integrity maintenance of C. gattii VGII strains.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-3688-4) contains supplementary material, which is available to authorized users.