The adaptive response to iron involves changes in energetic strategies in the pathogen Candida albicans

Extracellular BSA-degrading SAPs in the rare pathogen Meyerozyma guilliermondii strain SO as potential virulence factors in candidiasis

Meyerozyma guilliermondii (Candida guilliermondii) is one of the Candida species associated with invasive candidiasis. With the potential for expressing industrially important enzymes, M. guilliermondii strain SO possessed 99 % proteome similarity with the clinical ATCC 6260 isolate and showed pathogenicity towards zebrafish embryos. Recently, three secreted aspartyl proteinases (SAPs) were computationally identified as potential virulence factors in this strain without in vitro verification of SAP activity. The quantification of Candida SAPs activity in liquid broth were also scarcely reported. Thus, this study aimed to characterize M. guilliermondii strain SO's ability to produce SAPs (MgSAPs) in different conditions (morphology and medium) besides analyzing its growth profile. MgSAPs' capability to cleave bovine serum albumin (BSA) was also determined to propose that MgSAPs as the potential virulence factors compared to the avirulent Saccharomyces cerevisiae. M. guilliermondii strain SO produced more SAPs (higher activity) in yeast nitrogen base-BSA-dextrose broth compared to yeast extract-BSA-dextrose broth despite insignificantly different SAP activity in both planktonic and biofilm cells. FeCl3 supplementation significantly increased the specific protein activity (∼40 %). The BSA cleavage by MgSAPs at an acidic pH was proven through semi-quantitative SDS-PAGE, sharing similar profile with HIV-1 retropepsin. The presented work highlighted the MgSAPs on fungal cell wall and extracellular milieu during host infection could be corroborated to the quantitative production in different growth modes presented herein besides shedding lights on the potential usage of retropepsin's inhibitors in treating candidiasis. Molecular and expression analyses of MgSAPs and their deletion should be further explored to attribute their respective virulence effects.

Bibliometric analysis and thematic review of Candida pathogenesis: Fundamental omics to applications as potential antifungal drugs and vaccines

Invasive candidiasis caused by the pathogenic Candida yeast species has resulted in elevating global mortality. The pathogenicity of Candida spp. is not only originated from its primary invasive yeast-to-hyphal transition; virulence factors (transcription factors, adhesins, invasins, and enzymes), biofilm, antifungal drug resistance, stress tolerance, and metabolic adaptation have also contributed to a greater clinical burden. However, the current research theme in fungal pathogenicity could hardly be delineated with the increasing research output. Therefore, our study analysed the research trends in Candida pathogenesis over the past 37 years via a bibliometric approach against the Scopus and Web of Science databases. Based on the 3993 unique documents retrieved, significant international collaborations among researchers were observed, especially between Germany (Bernhard Hube) and the UK (Julian Naglik), whose focuses are on Candida proteinases, adhesins, and candidalysin. The prominent researchers (Neils Gow, Alistair Brown, and Frank Odds) at the University of Exeter and the University of Aberdeen (second top performing affiliation) UK contribute significantly to the mechanisms of Candida adaptation, tolerance, and stress response. However, the science mapping of co-citation analysis performed herein could not identify a hub representative of subsequent work since the clusters were semi-redundant. The co-word analysis that was otherwise adopted, revealed three research clusters; the cluster-based thematic analyses indicated the severeness of Candida biofilm and antifungal resistance as well as the elevating trend on molecular mechanism elucidation for drug screening and repurposing. Importantly, the in vivo pathogen adaptation and interactions with hosts are crucial for potential vaccine development.

Berberine inhibits Candida albicans growth by disrupting mitochondrial function through the reduction of iron absorption

AIMS

This study aimed to investigate whether berberine (BBR) can inhibit the iron reduction mechanism of Candida albicans, lowering the iron uptake of the yeast and perhaps having antimicrobial effects.

METHODS AND RESULTS

We determined that BBR may cause extensive transcriptional remodeling in C. albicans and that iron permease Ftr1 played a crucial role in this process through eukaryotic transcriptome sequencing. Mechanistic research showed that BBR might selectively inhibit the iron reduction pathway to lower the uptake of exogenous iron ions, inhibiting C. albicans from growing and metabolizing. Subsequent research revealed that BBR caused significant mitochondrial dysfunction, which triggered the process of mitochondrial autophagy. Moreover, we discovered that C. albicans redox homeostasis, susceptibility to antifungal drugs, and hyphal growth are all impacted by the suppression of this mechanism by BBR.

CONCLUSIONS

The iron reduction mechanism in C. albicans is disrupted by BBR, which disrupts mitochondrial function and inhibits fungal growth. These findings highlight the potential promise of BBR in antifungal applications.

The adaptive response to alternative carbon sources in the pathogen Candida albicans involves a remodeling of thiol- and glutathione-dependent redox status

Candida albicans is an opportunist pathogen responsible for a large spectrum of infections, from superficial mycosis to systemic diseases known as candidiasis. During infection in vivo, Candida albicans must adapt to host microenvironments and this adaptive response is crucial for the survival of this organism, as it facilitates the effective assimilation of alternative carbon sources others than glucose. We performed a global proteomic analysis on the global changes in protein abundance in response to changes in micronutrient levels, and, in parallel, explored changes in the intracellular redox and metabolic status of the cells. We show here that each of the carbon sources considered - glucose, acetate and lactate - induces a unique pattern of response in C. albicans cells, and that some conditions trigger an original and specific adaptive response involving the adaptation of metabolic pathways, but also a complete remodeling of thiol-dependent antioxidant defenses. Protein S-thiolation and the overproduction of reduced glutathione are two components of the response to high glucose concentration. In the presence of acetate, glutathione-dependent oxidative stress occurs, reduced thiol groups bind to proteins, and glutathione is exported out of the cells, these changes probably being triggered by an increase in glutathione-S-transferases. Overall, our results suggest that the role of cellular redox status regulation and defenses against oxidative stress, including the thiol- and glutathione-dependent response, in the adaptive response of C. albicans to alternative carbon sources should be reconsidered.

Development of Gum-Acacia-Stabilized Silver Nanoparticles Gel of Rutin against Candida albicans

Candida spp. is one of the most causative pathogens responsible for fungal infections. It is often a hospital-acquired form of sepsis with a very high number of deaths. Currently, the most effective anti-fungal agents are based on polyenes or echinocandins. However, long-term treatments or repeated use of these anti-fungals lead to therapy limitations. Current research is urgently needed to overcome existing challenges for antimicrobials from natural sources. This study aims to determine the anti-fungal activity of rutin, which has the advantage of increasing the therapeutic value. Because of its low solubility in water and oils, rutin is limited in use. To address these constraints, we encapsulated rutin in a nanocarrier system. Silver nanoparticles (SNPs) and gum acacia (GAs) are emerging as attractive components and are widely studied as biologically safe nanomaterials/carrier systems for various drugs. Still, they are barely investigated as nano-sized vectors for the targeted delivery of rutin. In the present work, GA stabilised SNPs of rutin were successfully formulated and evaluated. It was later incorporated into carbapol 940 gels and formed SNP gels. Rutin-SNPs were developed with a consistent size in the nano range of 59.67 ± 44.24 nm in size, 0.295 ± 0.014 polydispersity index (PDI), and −11.2 ± 6.66 mV zeta potential. The drug released was found to be 81. 26 ± 4.06% in 600 min by following zero-order kinetics. The rutin-SNP gel showed considerable activity against C. albicans skin candidiasis at MIC 1.56 g/mL. The developed formulation was biocompatible. This first-ever interdisciplinary study suggests that the rutin-SNPs gel could play a vital role in drug resistance in this fungal pathogen.

Combination Effect of Novel Bimetallic Ag–Ni Nanoparticles with Fluconazole against Candida albicans

The increasing frequency of antifungal drug resistance among pathogenic yeast “Candida” has posed an immense global threat to the public healthcare sector. The most notable species of Candida causing most fungal infections is Candida albicans. Furthermore, recent research has revealed that transition and noble metal combinations can have synergistic antimicrobial effects. Therefore, a one-pot seedless biogenic synthesis of Ag-Ni bimetallic nanoparticles (Ag–Ni NPs) using Salvia officinalis aqueous leaf extract is described. Various techniques, such as UV–vis, FTIR, XRD, SEM, EDX, and TGA, were used to validate the production of Ag-Ni NPs. The antifungal susceptibility of Ag-Ni NPs alone and in combination with fluconazole (FLZ) was tested against FLZ-resistant C. albicans isolate. Furthermore, the impacts of these NPs on membrane integrity, drug efflux pumps, and biofilms formation were evaluated. The MIC (1.56 μg/mL) and MFC (3.12 μg/mL) results indicated potent antifungal activity of Ag-Ni NPs against FLZ-resistant C. albicans. Upon combination, synergistic interaction was observed between Ag-Ni NPs and FLZ against C. albicans 5112 with a fractional inhibitory concentration index (FICI) value of 0.31. In-depth studies revealed that Ag-Ni NPs at higher concentrations (3.12 μg/mL) have anti-biofilm properties and disrupt membrane integrity, as demonstrated by scanning electron microscopy results. In comparison, morphological transition was halted at lower concentrations (0.78 μg/mL). From the results of efflux pump assay using rhodamine 6G (R6G), it was evident that Ag-Ni NPs blocks the efflux pumps in the FLZ-resistant C. albicans 5112. Targeting biofilms and efflux pumps using novel drugs will be an alternate approach for combatting the threat of multi-drug resistant (MDR) stains of C. albicans. Therefore, this study supports the usage of Ag-Ni NPs to avert infections caused by drug resistant strains of C. albicans.

AutoClassWeb: a simple web interface for Bayesian clustering of omics data

Objective

Data clustering is a common exploration step in the omics era, notably in genomics and proteomics where many genes or proteins can be quantified from one or more experiments. Bayesian clustering is a powerful unsupervised algorithm that can classify several thousands of genes or proteins. AutoClass C, its original implementation, handles missing data, automatically determines the best number of clusters but is not user-friendly.

Results

We developed an online tool called AutoClassWeb, which provides an easy-to-use and simple web interface for Bayesian clustering with AutoClass. Input data are entered as TSV files and quality controlled. Results are provided in formats that ease further analyses with spreadsheet programs or with programming languages, such as Python or R. AutoClassWeb is implemented in Python and is published under the 3-Clauses BSD license. The source code is available at https://github.com/pierrepo/autoclassweb along with a detailed documentation.

Genome Sequence and Analysis of the Flavinogenic Yeast Candida membranifaciens IST 626

The ascomycetous yeast Candida membranifaciens has been isolated from diverse habitats, including humans, insects, and environmental sources, exhibiting a remarkable ability to use different carbon sources that include pentoses, melibiose, and inulin. In this study, we isolated four C. membranifaciens strains from soil and investigated their potential to overproduce riboflavin. C. membranifaciens IST 626 was found to produce the highest concentrations of riboflavin. The volumetric production of this vitamin was higher when C. membranifaciens IST 626 cells were cultured in a commercial medium without iron and when xylose was the available carbon source compared to the same basal medium with glucose. Supplementation of the growth medium with 2 g/L glycine favored the metabolization of xylose, leading to biomass increase and consequent enhancement of riboflavin volumetric production that reached 120 mg/L after 216 h of cultivation. To gain new insights into the molecular basis of riboflavin production and carbon source utilization in this species, the first annotated genome sequence of C. membranifaciens is reported in this article, as well as the result of a comparative genomic analysis with other relevant yeast species. A total of 5619 genes were predicted to be present in C. membranifaciens IST 626 genome sequence (11.5 Mbp). Among them are genes involved in riboflavin biosynthesis, iron homeostasis, and sugar uptake and metabolism. This work put forward C. membranifaciens IST 626 as a riboflavin overproducer and provides valuable molecular data for future development of superior producing strains capable of using the wide range of carbon sources, which is a characteristic trait of the species.

Silver nanoparticles offer a synergistic effect with fluconazole against fluconazole-resistant Candida albicans by abrogating drug efflux pumps and increasing endogenous ROS

OBJECTIVES

A frequent emergence of drug resistance has been observed and posed great threat to global public health recently. This work aimed to investigate the potential synergistic effect and the underlying mechanisms of AgNPs-fluconazole combination more extensively through 2 clinically isolated fluconazole-resistant Candida albicans (C. albicans) strains.

METHODS

Antifungal properties of AgNPs and fluconazole alone or together against planktonic cells and biofilms were tested. Cellular and molecular targets associated with fluconazole resistance were monitored after AgNPs treatment. Antifungal potential of AgNPs-fluconazole combination was also explored in vivo using a mouse model of disseminated candidiasis. Tissue burden and survival rate were analyzed.

RESULTS

The results indicated that AgNPs worked synergistically with fluconazole against both planktonic cells of fluconazole-resistant C. albicans and biofilms formed <12 h. AgNPs treatment down-regulated ERG1, ERG11, ERG25, and CDR2, decreased membrane ergosterol levels and membrane fluidity, reduced membrane content of Cdr1p, Cdr2p, and thus efflux bump activity. The elevated ROS production was also a likely cause of the synergistic effect. In vivo, AgNPs and fluconazole combination significantly decreased the fungal burden and improved the survival rate of infected mice.

CONCLUSION

In conclusion, these results further confirm that AgNPs-fluconazole combination is a hopeful strategy for the treatment of fluconazole-resistant fungal infections.

Role of the high-affinity reductive iron acquisition pathway of Candida albicans in prostaglandin E2 production, virulence, and interaction with Pseudomonas aeruginosa

Components of the iron reductive pathway of Candida albicans have been implicated in the production of prostaglandin E2 (PGE2) and virulence. However, it is unknown whether other components of this pathway influence PGE2. We investigated the role of the iron reductive pathway of C. albicans in biofilm formation, PGE2 production, and virulence in Caenorhabditis elegans. Additionally, as the co-occurrence of C. albicans and Pseudomonas aeruginosa in host tissues is frequent and involves competition for host-associated iron, we examined the effects of this interaction. Deletion of multicopper oxidase gene, FET99, and iron permease genes, FTH1 and FTH2, affected biofilm metabolic activity, and for the FTH2 mutant, also biofilm morphology. Deletion of CCC1 (vacuolar iron transporter) and CCC2 (P-type ATPase copper importer) also influenced biofilm morphology. For PGE2 production, deletion of FET99, FTH1, FTH2, CCC1, and CCC2 caused a significant reduction by monomicrobial biofilms, while FTH2deletion caused the highest reduction in polymicrobial biofilms. URA3 positive mutants of FET99 and FTH2 demonstrated attenuated virulence in C. elegans, potentially due to the inability of mutants to form hyphae in vivo. Deductively, the role of the iron reductive pathway in PGE2 synthesis is indirect, possibly due to their role in iron homeostasis.

LAY SUMMARY

Iron uptake is vital for disease-causing microbes like Candida albicans. Using strains deficient in some iron-uptake genes, we show that iron-uptake genes, especially FET99 and FTH2, play a role in biofilm formation, prostaglandin production, and virulence in the nematode infection model.

Association of severe early childhood caries with salivary ferritin

Aim:

To evaluate salivary ferritin levels in children with severe early childhood caries (ECC).

Materials and Methods:

One hundred twenty participants were split into a study group that consisted of 60 children with severe ECC (dmft ≥5) and a control group that was free of caries. Both groups were age and gender-matched. Saliva was collected from both groups. Salivary ferritin was assessed using chemiluminescence microparticle immunoassay. The data obtained were statistically analyzed.

Results:

Salivary ferritin levels were higher in children with severe ECC (159.53 ± 18.65 μg/dl) compared to children with no caries (92.16 ± 12.91 μg/dl) and a highly significant statistical difference was seen (P < 0.001).

Conclusions:

Salivary ferritin levels were high with children having severe ECC.

Adaptation to iron deficiency in human pathogenic fungi

Iron is an essential micronutrient for virtually all eukaryotic organisms and plays a central role during microbial infections. Invasive fungal diseases are associated with strikingly high rates of mortality, but their impact on human health is usually underestimated. Upon a fungal infection, hosts restrict iron availability in order to limit the growth and virulence of the pathogen. Here, we use two model yeasts, Saccharomyces cerevisiae and Schizosaccharomyces pombe, to delve into the response to iron deficiency of human fungal pathogens, such as Candida glabrata, Candida albicans, Aspergillus fumigatus and Cryptococcus neoformans. Fungi possess common and species-specific mechanisms to acquire iron and to control the response to iron limitation. Upon iron scarcity, fungi activate a wide range of elegant strategies to capture and import exogenous iron, mobilize iron from intracellular stores, and modulate their metabolism to economize and prioritize iron utilization. Hence, iron homeostasis genes represent remarkable virulence factors that can be used as targets for the development of novel antifungal treatments.

The adaptive response to iron involves changes in energetic strategies in the pathogen Candida albicans

Candida albicans is an opportunist pathogen responsible for a large spectrum of infections, from superficial mycosis to systemic diseases known as candidiasis. Its ability to grow in different morphological forms, such as yeasts or filamentous hyphae, contributes to its survival in diverse microenvironments. Iron uptake has been associated with virulence, and C. albicans has developed elaborate strategies for acquiring iron from its host. In this work, we analyze the metabolic changes in response to changes in iron content in the growth medium and compare C. albicans adaptation to the presence or absence of iron. Functional and morphological studies, correlated to a quantitative proteomic analysis, were performed to assess the specific pathways underlying the response to iron, both in the yeast and filamentous forms. Overall, the results show that the adaptive response to iron is associated with a metabolic remodeling affecting the energetic pathways of the pathogen. This includes changes in the thiol-dependent redox status, the activity of key mitochondrial enzymes and the respiratory chain. Iron deficiency stimulates bioenergetic pathways, whereas iron-rich condition is associated with greater biosynthetic needs, particularly in filamentous forms. Moreover, we found that C. albicans yeast cells have an extraordinary capability to adapt to changes in environmental conditions.