Physicochemical characterization and antioxidant activity of melanin from a novel strain of Aspergillus bridgeri ICTF-201

Characterization of melanin from Exophiala mesophila with the prospect of potential biotechnological applications

Introducion

Fungal melanin is an underexplored natural biomaterial of great biotechnological interest in different areas. This study investigated the physical, chemical, electrochemical, and metal-binding properties of melanin extracted from the metallotolerant black fungus Exophiala mesophila strain IRTA-M2-F10.

Materials and methods

Specific inhibitory studies with tricyclazole and biochemical profiling of whole cells by synchrotron radiation-based Fourier-transform infrared spectral microscopy (SR-FTIRM) were performed. An optimized extraction protocol was implemented, and purified fungal melanin was characterized using an array of spectrophotometric techniques (UV-Vis, FTIR, and EPR) and by cyclic voltammetry (CV) experiments. The metal-binding capacity of melanin extracts was also assessed by using Cr(VI) as a model heavy metal.

Results

Inhibitory studies indicated that 1,8-dihydroxynaphthalene may be the main precursor molecule of E. mesophila melanin (DHN-melanin). The biochemical characterization of fungal melanin extracts were benchmarked against those from two melanins comprising the precursor molecule L-3,4-dihydroxiphenylalanine (DOPA-melanin): extracts from the ink of the cephalopod Sepia officinalis and DOPA-melanin synthesized in the laboratory. The CV results of melanin extracts incubated with and without cell suspensions of the electroconductive bacterium Geobacter sulfurreducens were indicative of novel semiquinone/hydroquinone redox transformations specific for each melanin type. These interactions may play an important role in cation exchange for the adsorption of metals and in microbial interspecies electron transfer processes.

Discussion

The obtained results provided further evidence for the DHN-nature of E. mesophila melanin. The FTIR profiling of melanin extracts exposed to Cr(VI), compared to unexposed melanin, resulted in useful information on the distinct surface-binding properties of fungal melanin. The parameters of the Langmuir and Freundlicht isotherms for the adsorption of Cr(VI) were determined and compared to bibliographic data. Altogether, the inherent properties of fungal melanin suggest its promising potential as a biomaterial for environmental applications.

Efficient production and characterization of melanin from Thermothelomyces hinnuleus SP1, isolated from the coal mines of Chhattisgarh, India

In the present study, fungi were isolated and screened from barren land in south-eastern Coalfields limited (SECL) in Chhattisgarh, India. Out of 14 isolated fungi, only three fungal isolates exhibited pigmentation in screening studies. The isolated fungal strain SP1 exhibited the highest pigmentation, which was further utilized for in vivo production, purification, and characterization of melanin pigment. The physical and chemical properties of the fungal pigment showed insolubility in organic solvents and water, solubility in alkali, precipitation in acid, and decolorization with oxidizing agents. The physiochemical characterization and analytical studies of the extracted pigment using ultraviolet-visible spectroscopy and Fourier transform infrared (FTIR) confirmed it as a melanin pigment. The melanin-producing fungus SP1 was identified as Thermothelomyces hinnuleus based on 18S-rRNA sequence analysis. Furthermore, to enhance melanin production, a response surface methodology (RSM) was employed, specifically utilizing the central composite design (CCD). This approach focused on selecting efficient growth as well as progressive yield parameters such as optimal temperature (34.4°C), pH (5.0), and trace element concentration (56.24 mg). By implementing the suggested optimal conditions, the production rate of melanin increased by 62%, resulting in a yield of 28.3 mg/100 mL, which is comparatively higher than the actual yield (17.48 ± 2.19 mg/100 mL). Thus, T. hinnuleus SP1 holds great promise as a newly isolated fungal strain that could be used for the industrial production of melanin.

The Metallotolerance and Biosorption of As(V) and Cr(VI) by Black Fungi

A collection of 34 melanized fungi isolated previously from anthropogenic contaminated sites were assessed for their tolerance to toxic concentrations of As(V) and Cr(VI) anions. Three strains of the species Cyphellophora olivacea, Rhinocladiella similis, and Exophiala mesophila (Chaetothyriales) were identified as hyper-metallotolerant, with estimated IC50 values that ranged from 11.2 to 16.9 g L-1 for As(V) and from 2.0 to 3.4 g L-1 for Cr(VI). E. mesophila and R. similis were selected for subsequent assays on their biosorption capacity and kinetics under different pH values (4.0 and 6.5) and types of biomass (active and dead cells and melanin extracts). The fungal biosorption of As(V) was relatively ineffective, but significant removal of Cr(VI) was observed from liquid cultures. The Langmuir model with second-order kinetics showed maximum sorption capacities of 39.81 mg Cr6+ g-1 for R. similis and 95.26 mg Cr6+ g-1 for E. mesophila on a dry matter basis, respectively, while the kinetic constant for these two fungi was 1.32 × 10-6 and 1.39 × 10-7 g (mg Cr6+ min)-1. Similar experiments with melanin extracts of E. mesophila showed maximum sorption capacities of 544.84 mg Cr6+ g-1 and a kinetic constant of 1.67 × 10-6 g (mg Cr6+ min)-1. These results were compared to bibliographic data, suggesting that metallotolerance in black fungi might be the result of an outer cell-wall barrier to reduce the diffusion of toxic metals into the cytoplasm, as well as the inner cell wall biosorption of leaked metals by melanin.

The Enigmatic World of Fungal Melanin: A Comprehensive Review

Synthetic dyes are generally not safe for human health or the environment, leading to the continuous search and growing demand for natural pigments that are considered safer, biodegrade more easily, and are environmentally beneficial. Among micro-organisms, fungi represent an emerging source of pigments due to their many benefits; therefore, they are readily viable on an industrial scale. Among all the bioactive pigments produced by fungi, melanin is an enigmatic, multifunctional pigment that has been studied for more than 150 years. This dark pigment, which is produced via the oxidative polymerization of phenolic compounds, has been investigated for its potential to protect life from all kingdoms, including fungi, from biotic and abiotic stresses. Over time, the research on fungal melanin has attracted a significant amount of scientific interest due to melanin's distinct biological activities and multifarious functionality, which is well-documented in the literature and could possibly be utilized. This review surveys the literature and summarizes the current discourse, presenting an up-to-date account of the research performed on fungal melanin that encompasses its types, the factors influencing its bioactivity, the optimization of fermentation conditions to enhance its sustainable production, its biosynthetic pathways, and its extraction, as well as biochemical characterization techniques and the potential uses of melanin in a wide range of applications in various industries. A massive scope of work remains to circumvent the obstacles to obtaining melanin from fungi and exploring its future prospects in a diverse range of applications.

A comparative study using response surface methodology and artificial neural network towards optimized production of melanin by Aureobasidium pullulans AKW

The effect of three independent variables (i.e., tyrosine, sucrose, and incubation time) on melanin production by Aureobasidium pullulans AKW was unraveled by two distinctive approaches: response surface methodology (i.e. Box Behnken design (BBD)) and artificial neural network (ANN) in this study for the first time ever using a simple medium. Regarding BBD, sucrose and incubation intervals did impose a significant influence on the output (melanin levels), however, tyrosine did not. The validation process exhibited a high consistency of BBD and ANN paradigms with the experimental melanin production. Concerning ANN, the predicted values of melanin were highly comparable to the experimental values, with minor errors competing with BBD. Highly comparable experimental values of melanin were achieved upon using BBD (9.295 ± 0.556 g/L) and ANN (10.192 ± 0.782 g/L). ANN accurately predicted melanin production and showed more improvement in melanin production by about 9.7% higher than BBD. The purified melanin structure was verified by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction pattern (XRD), and thermogravimetric analysis (TGA). The results verified the hierarchical architecture of the particles as small compasses by SEM analysis, inter-layer spacing in the XRD analysis, maximal atomic % for carbon, and oxygen atoms in the EDX analysis, and the great thermal stability in the TGA analysis of the purified melanin. Interestingly, the current novel endophytic strain was tyrosine-independent, and the uniquely applied ANN paradigm was more efficient in modeling the melanin production with appreciate amount on a simple medium in a relatively short time (168 h), suggesting additional optimization studies for further maximization of melanin production.

Melanin biopolymers from microbial world with future perspectives-a review

Melanin is an amorphous polymer made of heterogeneous functional groups synthesized by diverse organisms including fungi, bacteria, animals, and plants. It was widely acknowledged for its biological processes and its key role in the protection of organisms from environmental stress. Recently, melanin clutches attention in the field of nanobiotechnology, drug delivery, organic semiconductors and bioelectronics, environmental bioremediation, photoprotection, etc., Furthermore, melanin from natural sources like microbial community shows antimicrobial, fighting cancer, radical scavenging, cosmeceuticals, and many therapeutic areas as well. Though the multipotentiality nature of melanin has been put forth, real-world applications still flag fall behind, which might be anticipated to the inadequate and high price essence of natural melanin. However, current bioprocess technologies have paved for the large-scale or industrial production of microbial melanin, which could help in the replacement of synthetic melanin. Thus, this review emphasizes the various sources for melanin, i.e., types-based on its pathways and its chemical structures, functional efficiency, physical properties, and conventional and modern methods of both extraction and characterization. Moreover, an outlook on how it works in the field of medicine, bioremediation, and other related areas provides perspectives on the complete exploitation of melanin in practical applications of medicine and the environment.

Pyomelanin production via heterologous expression of 4-hydroxyphenylpyruvate dioxygenase (HPPD) and construction of HPPD inhibitor screening model

Melanin has an increasing market demand in cosmetics, food, medicine as well as aerospace due to its unique properties. Heterologous expression of 4-hydroxyphenylpyruvate dioxygenase (HPPD) from the melanin-producing strain Streptomyces fungicidicus NW-EN1 in Escherichia coli shortened the fermentation cycle of melanin. HPPD catalyzed 4-hydrophenylpyruvate (HPP) to form homologous acid (HGA) and finally form melanin. The purified melanin had the highest absorption peak at 460 nm. Fourier transform infrared spectroscopy and scanning electron microscope scanning showed that the pigment had universal characteristic peaks. The presence of HGA, a predictor of pyomelanin, was identified by high-performance liquid chromatography analysis. The recombinant E. coli produced 804.4 ± 5.9 mg/L pyomelanin within 48 h. Metal ions had a great influence on the production of pyomelanin. Pyomelanin was stable in response to light intensity and had a protective effect against bacteria under UV irradiation. Meanwhile, we utilized the chromogenic effect after whole-cell catalysis to reflect the inhibition of the HPPD inhibitors (mesotrione and isoxaflutole) on HPPD by observing the color change. As a rapid method to test the action of inhibitors, this method is expected to be useful for the development of HPPD-inhibiting herbicides.

Gene expression, molecular docking, and molecular dynamics studies to identify potential antifungal compounds targeting virulence proteins/genes VelB and THR as possible drug targets against Curvularia lunata

Curvuluria lunata is a melanized fungus pathogenic to both plants and animals including humans, causing from mild, febrile to life-threatening illness if not well treated. In humans, it is an etiological agent of keratomycosis, sinusitis, and onychomycosis in immunocompromised and immunocompetent patients. The development of multiple-drug-resistant strains poses a critical treatment issue as well as public health problem. Natural products are attractive prototypes for drug discovery due to their broad-spectrum efficacy and lower side effects. The present study explores possible targets of natural antifungal compounds (α-pinene, eugenol, berberine, and curcumin) against C. lunata via gene expression analysis, molecular docking interaction, and molecular dynamics (MD) studies. Curcumin, berberine, eugenol, and α-pinene exhibited in vitro antifungal activity at 78 μg/ml, 156 μg/ml, 156 μg/ml, and 1250 μg/ml, respectively. In addition, treatment by these compounds led to the complete inhibition of conidial germination and hindered the adherence when observed on onion epidermis. Several pathogenic factors of fungi are crucial for their survival inside the host including those involved in melanin biosynthesis, hyphal growth, sporulation, and mitogen-activated protein kinase (MAPK) signalling. Relative gene expression of velB, brn1, clm1, and pks18 responsible for conidiation, melanin, and cell wall integrity was down-regulated significantly. Results of molecular docking possessed good binding affinity of compounds and have confirmed their potential targets as THR and VelB proteins. The docked structures, having good binding affinity among all, were further refined, and rescored from their docked poses through 100-ns long MD simulations. The MDS study revealed that curcumin formed a stable and energetically stabilized complex with the target protein. Therefore, the study concludes that the antifungal compounds possess significant efficacy to inhibit C. lunata growth targeting virulence proteins/genes involved in spore formation and melanin biosynthesis.

Design and synthesis of eugenol/isoeugenol glycoconjugates and other analogues as antifungal agents against Aspergillus fumigatus

Glycoconjugates are biologically significant molecules as they tend to serve a wide range of intra- and extra-cellular processes depending on their size and complexity. The secondary metabolites of the plant Myristica fragrans, eugenol and isoeugenol, have shown antifungal activities (IC50 1900 μM). Therefore, we envisioned that glycoconjugates based on these two scaffolds could prove to be potent antifungal agents. Triazole-containing compounds have shown prominent activities as antifungal agents. Based on this, we opined that a Cu(i) catalyzed click reaction could serve as the bridging tool between a eugenol/isoeugenol moiety and sugars to synthesize eugenol/isoeugenol based glycoconjugates. In our present work, we have coupled propargylated eugenol/isoeugenol and azido sugar to furnish eugenol/isoeugenol based glycoconjugates. In another approach, we have carried out hydroxylation of the double bond of eugenol and subsequent azidation of a primary alcohol followed by intramolecular coupling reactions leading to various other analogues. All the synthesized compounds were assayed against an opportunistic pathogenic fungus, Aspergillus fumigatus. Among the synthesized compounds, two analogues have exhibited significant antifungal activities with IC50 values of 5.42 and 9.39 μM, respectively. The study suggested that these two analogues inhibit cell wall-associated melanin hydrophobicity along with the number of conidia. The synthesized compounds were found to be non-cytotoxic to an untransformed cell line.

Microbial polyketides and their roles in insect virulence: from genomics to biological functions

Covering: May 1966 up to January 2022Entomopathogenic microorganisms have potential for biological control of insect pests. Their main secondary metabolites include polyketides, nonribosomal peptides, and polyketide-nonribosomal peptide (PK-NRP) hybrids. Among these secondary metabolites, polyketides have mainly been studied for structural identification, pathway engineering, and for their contributions to medicine. However, little is known about the function of polyketides in insect virulence. This review focuses on the role of bacterial and fungal polyketides, as well as PK-NRP hybrids in insect infection and killing. We also discuss gene distribution and evolutional relationships among different microbial species. Further, the role of microbial polyketides and the hybrids in modulating insect-microbial symbiosis is also explored. Understanding the mechanisms of polyketides in insect pathogenesis, how compounds moderate the host-fungus interaction, and the distribution of PKS genes across different fungi and bacteria will facilitate the discovery and development of novel polyketide-derived bio-insecticides.

Suggested Sustainable Medical and Environmental Uses of Melanin Pigment From Halotolerant Black Yeast Hortaea werneckii AS1

The marine ecosystem is a complex niche with unique environmental circumstances. Microbial communities from the sea are one of the main origins of compounds with tremendous capabilities. Marine yeasts have the ability to produce secondary metabolites that are architecturally distinct from those found in terrestrial species. Melanin pigment synthesized by marine halotolerant black yeast Hortaea werneckii AS1 isolated from Mediterranean salt lakes in Alexandria, Egypt was found to exert a radical scavenging effect on 2,2-diphenyl-1-picrylhydrazyl (DPPH) with an IC₅₀ of 61.38 μg/ml. Furthermore, it showed no cytotoxicity toward human skin fibroblast cell line (HSF) with an IC₅₀ value above 0.1 mg/ml. The antimicrobial capability of the pigment was revealed against the tested number of bacterial and fungal strains with the highest inhibition zone of 25 mm against Aeromonas sp. and a growth inhibition percentage up to 63.6% against Aspergillus niger. From an environmental impact point of view, the pigment disclosed a heavy metal removal efficiency of 85.7, 84.8, and 81.5% for Pb²⁺, Cd²⁺, and Ni²⁺, respectively, at 100 mg/L metal concentration. The previously mentioned results suggested melanin from H. werneckii AS1 as a promising biocompatible candidate in various medical, cosmetics, pharmaceutical, and environmental applications.

New insights and advances on pyomelanin production: from microbial synthesis to applications

Pyomelanin is a brown-black phenolic polymer and results from the oxidation of homogentisic acid (HGA) in the L-tyrosine pathway. As part of the research for natural and active ingredients issued from realistic bioprocesses, this work re-evaluates the HGA pigment and makes an updated inventory of its syntheses, microbial pathways, and properties, with tracks and recent advances for its large-scale production. The mechanism of the HGA polymerization is also well documented. In alkaptonuria, pyomelanin formation leads to connective tissue damages and arthritis, most probably due to the ROS issued from HGA oxidation. While UV radiation on human melanin may generate degradation products, pyomelanin is not photodegradable, is hyperthermostable, and has other properties better than the L-Dopa melanin. This review aims to raise awareness about the potential of this pigment for various applications, not only for skin coloring and protection but also for other cells, materials, and as a promising (semi)conductor for bioelectronics and energy.

Optimization of melanin pigment production from the halotolerant black yeast Hortaea werneckii AS1 isolated from solar salter in Alexandria

Background

Melanins are one of the magnificent natural pigments synthesized by a wide range of microorganisms including different species of fungi and bacteria. Marine black yeasts appear to be potential prospects for the synthesis of natural melanin pigment. As a result, the goal of this research was to isolate a marine black yeast melanin-producing strain and improve the culturing conditions in order to maximize the yield of such a valuable pigment.

Results

Among five locally isolated black yeast strains, the only one that demonstrated a potent remarkable melanin pigment production was identified using ITS rDNA as Hortaea werneckii AS1. The extracted pigment’s physiochemical characterization and analytical investigation with Ultraviolet-Visible (UV) spectrophotometry, Fourier Transform-Infrared spectroscopy (FTIR), and Scanning Electron Microscope (SEM) confirmed its nature as a melanin pigment. The data obtained from the polynomial model’s maximum point suggested that CaCl₂, 1.125 g/L; trace element, 0.25 ml/L; and a culture volume 225 mL/500 mL at their optimal values were the critical three elements impacting melanin production. In comparison with the baseline settings, the response surface methodology (RSM) optimization approach resulted in a 2.0 - fold improvement in melanin output.

Conclusions

A maximum melanin yield of 0.938 g/L proved the halotolerant H. werneckii AS1 potentiality as a source for natural melanin pigment synthesis ‘when compared to some relevant black yeast strains’ and hence, facilitating its incorporation in a variety of pharmaceutical and environmental applications.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02505-1.

Melanin and Melanin-Functionalized Nanoparticles as Promising Tools in Cancer Research-A Review

Cancer poses an ongoing global challenge, despite the substantial progress made in the prevention, diagnosis, and treatment of the disease. The existing therapeutic methods remain limited by undesirable outcomes such as systemic toxicity and lack of specificity or long-term efficacy, although innovative alternatives are being continuously investigated. By offering a means for the targeted delivery of therapeutics, nanotechnology (NT) has emerged as a state-of-the-art solution for augmenting the efficiency of currently available cancer therapies while combating their drawbacks. Melanin, a polymeric pigment of natural origin that is widely spread among many living organisms, became a promising candidate for NT-based cancer treatment owing to its unique physicochemical properties (e.g., high biocompatibility, redox behavior, light absorption, chelating ability) and innate antioxidant, photoprotective, anti-inflammatory, and antitumor effects. The latest research on melanin and melanin-like nanoparticles has extended considerably on many fronts, allowing not only efficient cancer treatments via both traditional and modern methods, but also early disease detection and diagnosis. The current paper provides an updated insight into the applicability of melanin in cancer therapy as antitumor agent, molecular target, and delivery nanoplatform.

Natural Melanin: Current Trends, and Future Approaches, with Especial Reference to Microbial Source

Melanin is a universal natural dark polymeric pigment, arising in microorganisms, animals, and plants. There is a couple of pieces of literature on melanin, each focusing on a different issue, the goal of the present review is to focus on microbial melanin. It has numerous benefits with very few drawbacks. The current situation and expected trends are discussed. Intriguing, numerous studies have provoked a serious necessity for a comprehensive assessment of microbial melanin pigments. So that, such review would help scholars from diverse backgrounds to realize the importance of melanin pigments isolated from microorganisms, with this aim in mind, information, and hypothesis from this review could be the paradigm for studies on melanin in the next era.

Isoeugenol affects expression pattern of conidial hydrophobin gene RodA and transcriptional regulators MedA and SomA responsible for adherence and biofilm formation in Aspergillus fumigatus

Aspergillus fumigatus is one of the major pathogenic fungal species, causing life-threatening infections. Due to a limited spectrum of available antifungals, exploration of new drug targets as well as potential antifungal molecules has become pertinent. Rodlet layer plays an important role in adherence of fungal conidia to hydrophobic cell surfaces in host, which also leads to A. fumigatus biofilm formation, contributing factor to fungal pathogenicity. From decades, natural sources have been known for the development of new active molecules. The present study investigates effect of isoeugenol on genes responsible for hydrophobins (RodA), adhesion as well as biofilm formation (MedA and SomA) of A. fumigatus. Minimum inhibitory concentrations (MIC and IC₅₀) of isoeugenol against A. fumigatus were determined using broth microdilution assay. The IC₅₀ results showed reduced hydrophobicity and biofilm formation as well as eradication after treatment with the compound and electron micrograph data corroborated these findings. The qRT-PCR showed a significant downregulation of genes RodA, MedA, SomA and pksP involved in hydrophobicity and biofilm formation. SwissADME studies potentiated drug-like propensity for isoeugenol which formed four hydrogen bonds with low binding energy (− 4.54 kcal/mol) at the catalytic site of RodA protein studied via AutoDock4. Hence, the findings conclude that isoeugenol inhibits conidial hydrophobicity and biofilm formation of A. fumigatus and further investigations are warranted in this direction.

The Dark Pigment in the Sesame (Sesamum indicum L.) Seed Coat: Isolation, Characterization, and Its Potential Precursors

Sesame is a worldwide oilseed crop used in the food pharmacy. Its seed phenotypes determine the seed quality values. However, a thorough assessment of seed coat metabolites is lacking, and the dark pigment in the seed coat is not well-characterized. Herein, we report the isolation of melanin by the alkali method from the black and brown sesame seeds. Physicochemical methods, including scanning electron microscopy (SEM), solubility, precipitation, UV-Vis spectroscopy, Fourier transform infrared (FT-IR) spectroscopy, and thermogravimetric-differential scanning calorimetry (TG-DSC), were used to characterize the sesame melanins. The results clearly showed that the isolated pigments were similar to melanin from other sources. Both melanins were heat-stable and exhibited numerous characteristic absorption peaks. Through a comprehensible LC-MS/MS-based metabolome profiles analysis of NaOH and methanol extracts of black and white sesame seeds, caffeic, protocatechuic, indole-carboxylic, homogentisic, ferulic, vanillic, and benzoic acids were identified as the potential precursors of the sesame melanin. Our findings widen our understanding of dark seeds pigmentation in sesame. Furthermore, they show that black sesame seeds are promising sources of edible melanin for food and biotechnological applications.

Characterization and biological activities of melanin pigment from root endophytic fungus, Phoma sp. RDSE17

Melanins are high molecular weight hydrophobic pigments which have gained popularity for their role in virulence against different pathogens. In the present study, we isolated and characterized the melanin pigment produced by a dark septate endophyte fungus Phoma sp. RDSE17, which was associated with the roots of an indigenous Oryza sativa cv. 'Chakhao amubi' in Manipur, Northeast India. The biological properties of purified melanin from the fungus were evaluated for their antioxidant, antimicrobial and anticancerous activities. The pigment was extracted from Phoma sp. by alkaline-acid hydrolysis method and confirmed as melanin through physico-chemical tests and spectral (UV, FTIR, and EPR) analysis. The analyses of the elemental composition indicated that the pigment possessed a low percentage of nitrogen (N) contents, and therefore, would not fall under DOPA class of melanin. Exposure of the fungus to melanin pathway inhibitors revealed a positive melanin inhibition by tricyclazole, but not by kojic acid. Thus, the melanin from Phoma sp. may be a member of the DHN family. Moreover, the purified melanin showed high DPPH (1, 1-Diphenyl-2-picrylhydrazyl) free radical-scavenging activity with an EC₅₀ of 69 µg/mL and inhibited human lung cancer cell (A549 cells) proliferation at 80 µg/mL. The present study demonstrates that melanin from Phoma sp. RDSE17 could be employed as a potential biological (antioxidant) and antimicrobial agent for inhibiting the growth of humans and phytopathogens.

Phenotypic Switching of B16F10 Melanoma Cells as a Stress Adaptation Response to Fe3O4/Salicylic Acid Nanoparticle Therapy

Melanoma is a melanocyte-derived skin cancer that has a high heterogeneity due to its phenotypic plasticity, a trait that may explain its ability to survive in the case of physical or molecular aggression and to develop resistance to therapy. Therefore, the therapy modulation of phenotypic switching in combination with other treatment modalities could become a common approach in any future therapeutic strategy. In this paper, we used the syngeneic model of B16F10 melanoma implanted in C57BL/6 mice to evaluate the phenotypic changes in melanoma induced by therapy with iron oxide nanoparticles functionalized with salicylic acid (SaIONs). The results of this study showed that the oral administration of the SaIONs aqueous dispersion was followed by phenotypic switching to highly pigmented cells in B16F10 melanoma through a cytotoxicity-induced cell selection mechanism. The hyperpigmentation of melanoma cells by the intra- or extracellular accumulation of melanic pigment deposits was another consequence of the SaIONs therapy. Additional studies are needed to assess the reversibility of SaIONs-induced phenotypic switching and the impact of tumor hyperpigmentation on B16F10 melanoma’s progression and metastasis abilities.

Bioinspired Living Coating System in Service: Evaluation of the Wood Protected with Biofinish during One-Year Natural Weathering

The service life performance of timber products exposed to natural weathering is a critical factor limiting the broad use of wood as an external building element. The goal of this study was to investigate the in-service characterization of an innovative biofinish coating system. It is a novel surface finishing solution based on the bioinspired concept of living fungal cells designed for effective wood protection. The performance of Scots pine (Pinus sylvestris L.) wood coated with biofinish was compared with uncoated references. Samples were exposed to natural weathering for 12 months under the climatic conditions of northern Italy. The visual appearance, colour, gloss, wettability, and 3D surface topography of the wood surface were examined. Results revealed that the total colour changes (∆E) of biofinish-coated wood were negligible. Untreated Scots pine wood revealed the changes in colour after just three months of exposure. The gloss changes of both surface types were small. The contact angle measured on biofinish-coated wood was higher compared to that of uncoated Scots pine. Surface roughness increased in uncoated wood due to the erosion effect caused by the weathering progress. Conversely, the surface roughness of biofinish-coated samples decreased along the exposure time. This phenomenon was explained by two self-healing mechanisms: migration of non-polymerized oil to the cracked surface, where it polymerizes and creates a closed layer, and local regrowth to cover damaged spots by living fungal cells present in the coating. The obtained results revealed the superior aesthetic performance of the biofinish surface treatment against natural weathering. By considering the fully bio-based nature of the investigated coating, it was concluded that this solution can be an attractive alternative for state-of-the-art wood protection technologies.

Microbial melanin: Recent advances in biosynthesis, extraction, characterization, and applications

Melanin is a common name for a group of biopolymers with the dominance of potential applications in medical sciences, cosmeceutical, bioremediation, and bioelectronic applications. The broad distribution of these pigments suggests their role to combat abiotic and biotic stresses in diverse life forms. Biosynthesis of melanin in fungi and bacteria occurs by oxidative polymerization of phenolic compounds predominantly by two pathways, 1,8-dihydroxynaphthalene [DHN] or 3,4-dihydroxyphenylalanine [DOPA], resulting in different kinds of melanin, i.e., eumelanin, pheomelanin, allomelanin, pyomelanin, and neuromelanin. The enzymes responsible for melanin synthesis belong mainly to tyrosinase, laccase, and polyketide synthase families. Studies have shown that manipulating culture parameters, combined with recombinant technology, can increase melanin yield for large-scale production. Despite significant efforts, its low solubility has limited the development of extraction procedures, and heterogeneous structural complexity has impaired structural elucidation, restricting effective exploitation of their biotechnological potential. Innumerable studies have been performed on melanin pigments from different taxa of life in order to advance the knowledge about melanin pigments for their efficient utilization in diverse applications. These studies prompted an urgent need for a comprehensive review on melanin pigments isolated from microorganisms, so that such review encompassing biosynthesis, bioproduction, characterization, and potential applications would help researchers from diverse background to understand the importance of microbial melanins and to utilize the information from the review for planning studies on melanin. With this aim in mind, the present report compares conventional and modern ideas for environment-friendly extraction procedures for melanin. Furthermore, the characteristic parameters to differentiate between eumelanin and pheomelanin are also mentioned, followed by their biotechnological applications forming the basis of industrial utilization. There lies a massive scope of work to circumvent the bottlenecks in their isolation and structural elucidation methodologies.

Correlation between the synthesis of pullulan and melanin in Aureobasidium pullulans

The content of pullulan and melanin in 500 mutants of Aureobasidum pullulans obtained by ultraviolet mutagenesis were examined and statistically analyzed, and a strong positive correlation was found between them. The result was further confirmed by culturing wild type strain As3.3984 in different media. Then we constructed melanin-deletion mutant As-Δalb1 and pullulan-deletion mutant As-Δpul. As-Δalb1 was a melanin-free strain with the yield of pullulan decreased by 41.01%. The supplementation of melanin in the culture of As-Δalb1 increased the production of pullulan. As-Δpul synthesized neither pullulan nor melanin and recovered melanin synthesis by adding pullulan to the medium. The results suggested that high concentration- of pullulan induced morphological transformation and synthesis of melanin, and melanin promoted the synthesis of pullulan. The pullulan biosynthetic genes, upt, pgm, ugp, and pul, were down-regulated, while the negative regulatory gene of pullulan synthesis, creA, was up-regulated by melanin deficiency.

New insight into melanin for food packaging and biotechnology applications

Melanin is a dark brown to black biomacromolecule with biologically active multifunctional properties that do not have a precise chemical structure, but its structure mainly depends on the polymerization conditions during the synthesis process. Natural melanin can be isolated from various animal, plant, and microbial sources, while synthetic melanin-like compounds can be synthesized by simple polymerization of dopamine. Melanin is widely used in various areas due to its functional properties such as photosensitivity, light barrier property, free radical scavenging ability, antioxidant activity, etc. It also has an excellent ability to act as a reducing agent and capping agent to synthesize various metal nanoparticles. Melanin nanoparticles (MNP) or melanin-like nanoparticles (MLNP) have the unique potential to act as functional materials to improve nanocomposite films' physical and functional properties. Various food packaging and biomedical applications have been made alone or by mixing melanin or MLNP. In this review, the general aspects of melanin that highlight biological activity, along with a description of MNP and the use as nanofillers in packaging films as well as reducing and capping agents and biomedical applications, were comprehensively reviewed.

Deletion of pksA attenuates the melanogenesis, growth and sporulation ability and causes increased sensitivity to stress response and antifungal drugs in the human pathogenic fungus Fonsecaea monophora

Fonsecaea monophora, which is very similar to Fonsecaea pedrosoi in morphological features, has been commonly misdiagnosed as F. pedrosoi. Like F. pedrosoi, F. monophora has been also identified as a predominant pathogen of Chromoblastomycosis (CBM). Melanin has been recognized as a virulence factor in several fungi, however, it is still largely unknown about the biological role of melanin and how melanin is synthesized in F. monophora. In this study, we identified two putative polyketide synthase genes (pks), AYO21_03016 (pksA) and AYO21_10638, by searching against the genome of F. monophora. AYO21_03016 and AYO21_10638 were further targeted disrupted by Agrobacterium tumefaciens-mediated transformation (ATMT). We discovered that pksA gene was the major polyketide synthase required for melanin synthesis in F. monophora, rather than AYO21_10638. Phenotypic analysis showed that, knocking out of the pksA gene attenuated melanogenesis, growth rate, sporulation ability and virulence of F. monophora, as compared with wild-type and complementation strain (pksA-C). Furthermore, the ΔpksA mutant was confirmed to be more sensitive to the oxidative stress, extreme pH environment, and antifungal drugs including itraconazole (ITC), terbinafine (TER), and amphotericin B (AMB). Taken together, these findings enabled us to comprehend the role of pksA in regulating DHN-melanin pathway and its effect on the biological function of F. monophora.

Inhibition of Staphylococcus aureus LC554891 by Moringa oleifera Seed Extract either Singly or in Combination with Antibiotics

Bacterial outbreaks caused by Staphylococcus aureus (S. aureus) are interesting due to the existence of multidrug resistant (MDR) isolates. Therefore, there is a need to develop novel ways to control such MDR S. aureus. In this study, some natural agents such as honey bee (HB), extracts of either Moringa oleifera seeds (MSE), or leaves (MLE) and essential oils of garlic, clove, and moringa were studied for their inhibitory activity against this S. aureus pathogen. About 100 food samples including beef luncheon (n = 25), potato chips (n = 50), and corn flakes (n = 25) were investigated for possible pollution with the S. aureus bacteria. The isolated bacteria suspected to belong S. aureus that grew well onto Baird-Parker agar (Oxoid) and shiny halo zones and positive coagulase reaction were selected and identified by API-Kits; all of them that were approved belong to S. aureus (18 strains). The sensitivity of the obtained 18 S. aureus bacterial strains to 12 antibiotics were evaluated; all of them were resistant to ofloxacin; however, other antibiotics tested showed variable results. Interestingly, the S. aureus No. B3 isolated from beef luncheon was resistant to10 antibiotics out of 12 ones tested. Multiple antibiotic resistance index (MAR) of this S. aureus strain was about 83.3%. Therefore, its identification was confirmed by sequencing of a 16S rRNA gene which approved a successful biochemical identification carried out by API Kits and such strain was designated S. aureus LC 554891. The genome of such strain appeared to contain mecA gene encoding methicillin resistance; it was found to contain hla, hlb, tsst-1, and finbA that encode α-blood hemolysis, β-blood hemolysis, toxic shock syndrome gene, and fibrinogen-binding protein gene, respectively. In addition, the virulence factors viz. sea; seb; sec encoding enterotoxins were detected in the DNA extracted from S. aureus B3 strain. Aqueous extract of Moringa oleifera seeds (MSE) showed inhibitory activity against S. aureus LC 554891 better than that obtained by tetracycline, essential oils or HB. Minimum inhibitory concentration (MIC) of MSE was 20µg/mL. Instrumental analysis of MSE showed 14 bioactive chemical compounds. Combinations of both MSE and tetracycline showed distinctive inhibitory activity against S. aureus LC 554891 than that obtained by either tetracycline or MSE singly.

Biological activities of melanin pigment extracted from Bombyx mori gut-associated yeast Cryptococcus rajasthanensis KY627764

Melanin pigment has been produced and extracted from a wide variety of living forms ranging from microorganisms to higher organisms. Owing to the therapeutic nature of the pigment, various microbial populations have been explored for its production. Hence, we isolated a melanin producing yeast from the insect Bombyx mori gut microflora and identified it as Cryptococcus rajasthanensis based on the molecular characterization. The isolated yeast produced enhanced melanin pigment when cultured in the minimal L-tyrosine broth as compared to the Saboraud medium. The pigment was extracted and characterized as melanin based on UV-Visible spectroscopy, FTIR (Fourier-transform infrared) spectroscopy and ¹H NMR (Nuclear magnetic resonance). The melanin pigment was evaluated as a potent bioactive molecule with bioactivity like antimicrobial, antioxidant, anti-inflammatory, and anticancer activity that describes the therapeutic nature of the extracted melanin pigment. Distinct from the biologically active role the melanin pigment isolated from the yeast, the Cryptococcus extract also exhibited killer toxin activity against the pathogenic yeast Candida albicans.

Comprehensive utilization of edible mushroom Auricularia auricula waste residue-Extraction, physicochemical properties of melanin and its antioxidant activity

In order to promote the comprehensive utilization of the Auricularia auricula waste residue, the extraction process and the physicochemical properties of melanin from A. auricula waste residue were studied. Furthermore, the chemical antioxidant activity of waste residue melanin and its protective effect on cell oxidative injury induced by H2O2 were investigated. The results indicated that the ultrasonic-assisted extraction process could be used to extract the melanin from A. auricula waste residue. Melanin had a good solubility in alkali solution and exhibited a certain stability to thermal. There was no significant difference between A. auricula melanin control group and waste residue melanin on ABTS, DPPH, and hydroxyl radical scavenging activity. Waste residue melanin significantly inhibited the cell death caused by H2O2, and the cell viability was restored to 98.09 ± 5.97% when the melanin concentration was 1.6 mg/ml. Cell morphology observation confirmed that the melanin ameliorated the morphological changes of cells induced by oxidative stress.

Fungal Diversity in Intertidal Mudflats and Abandoned Solar Salterns as a Source for Biological Resources

Intertidal zones are unique environments that are known to be ecological hot spots. In this study, sediments were collected from mudflats and decommissioned salterns on three islands in the Yellow Sea of South Korea. The diversity analysis targeted both isolates and unculturable fungi via Illumina sequencing, and the natural recovery of the abandoned salterns was assessed. The phylogeny and bioactivities of the fungal isolates were investigated. The community analysis showed that the abandoned saltern in Yongyudo has not recovered to a mudflat, while the other salterns have almost recovered. The results suggested that a period of more than 35 years may be required to return abandoned salterns to mudflats via natural restoration. Gigasporales sp. and Umbelopsis sp. were selected as the indicators of mudflats. Among the 53 isolates, 18 appeared to be candidate novel species, and 28 exhibited bioactivity. Phoma sp., Cladosporium sphaerospermum, Penicillium sp. and Pseudeurotium bakeri, and Aspergillus urmiensis showed antioxidant, tyrosinase inhibition, antifungal, and quorum-sensing inhibition activities, respectively, which has not been reported previously. This study provides reliable fungal diversity information for mudflats and abandoned salterns and shows that they are highly valuable for bioprospecting not only for novel microorganisms but also for novel bioactive compounds.

Melanin incorporated electroactive and antioxidant silk fibroin nanofibrous scaffolds for nerve tissue engineering

Nerve restoration and repair in the central nervous system is complicated and requires several factors to be considered while designing the scaffolds like being bioactive as well as having neuroinductive, neuroconductive and antioxidant properties. Aligned electrospun nanofibers provide necessary guidance and topographical cues required for directing the axonal and neurite outgrowth during regeneration. Conduction of nerve impulses is a mandatory feature of a typical nerve. The neuro-conductive property can be imparted by blending the biodegradable, bioactive polymers with conductive polymers. This will provide additional features, i.e., electrical cues to the already existing topographical and bioactive cues in order to make it a more multifaceted neuroregenerative approach. Hence in the present study, we used a combination of silk fibroin and melanin for the fabrication of random and aligned electrospun nanofibrous composite scaffolds. We performed the physico-chemical characterization and also assessed their antioxidant properties. We also evaluated their neurogenic potential using human neuroblastoma cells (SH-SY5Y) for their cellular viability, proliferation, adhesion and differentiation levels. Designed nanofibrous scaffolds had adequate physical properties suitable as neural substrates to promote neuronal growth and regeneration. They stimulated the neuroblastoma cell attachment and viability indicating their biocompatible nature. Silk/melanin composite scaffolds have specifically exhibited high antioxidant nature proven by the radical scavenging activity. Additionally, the melanin incorporated aligned silk fibroin scaffolds promoted the cell differentiation into neurons and orientation along their axis. Our results confirmed the potential of melanin incorporated aligned silk fibroin scaffolds as the promising candidates for effective nerve regeneration and recovery.

Melanin particles isolated from the fungus Fonsecaea pedrosoi activates the human complement system

BACKGROUND

Melanin production has been associated with virulence in various pathogenic fungi, including Fonsecaea pedrosoi, the major etiological agent for chromoblastomycosis, a subcutaneous fungal disease that occurs in South America.

OBJECTIVE

The aim of this study was to evaluate the effects of acid-basic extracted F. pedrosoi melanin particles and fungal cell ghosts obtained by Novozym 234 treatment on their ability to activate the human complement system.

METHODS

The ability of melanin particles and fungal cell ghosts to activate the human complement system was evaluated by complement consumption, immunofluorescence, and enzyme-linked immunosorbent assay (ELISA).

FINDINGS

Unsensitised melanin particles and melanin ghosts presented complement consumption of 82.67 ± 2.08% and 96.04 ± 1.13%, respectively. Immunofluorescence assays revealed intense deposition of the C3 and C4 fragments on the surface of melanin particles and ghosts extracted from F. pedrosoi. Deposition of the C3, C4, and C5 fragments onto melanin samples and zymosan was confirmed by ELISA. Deposition of small amounts of C1q and C9 onto melanin samples and zymosan was detected by ELISA.

CONCLUSION

Fonsecaea pedrosoi melanin particles and fungal cell ghosts activated the complement system mainly through an alternative pathway.

Optimisation and characterisation of the orange pigment produced by a cold adapted strain of Penicillium sp. (GBPI_P155) isolated from mountain ecosystem

With globalisation and growing health risks of synthetic colourants, search for pigments from natural sources has increased owing to their non-toxic nature. The present study highlights the bioprospection of natural pigment from a cold adapted fungal strain of Penicillium sp. (GBPI_P155), isolated from soil of Indian Himalayan region. The fungus produced insoluble and orange-coloured pigment in liquid medium with maximum production recorded in potato dextrose (PD) broth at 15°C and 3 pH, while maximum biomass was produced at 25°C and pH 3. While examining the effect of different mineral salts, and carbon and nitrogen sources on pigment production, maximum accumulation of pigment was recorded in PD broth supplemented with 2% maltose. Following production, extraction of pigment was performed using chloroform and characterised partially by UV/vis (λmax at 495 nm and a shoulder peak at 530 nm) and Fourier Transform Infrared (FT-IR) spectroscopy. Thin layer chromatography of chloroform extract resulted in separation of pigment in three fractions with Rf values 0.911, 0.852 and 0.808, which were further analysed using Liquid Chromatography Mass Spectrometry (LC/MS). The overall approach resulted in identification of pigment as a mixture of different derivatives of carotenoids. The extracted pigment also possessed antimicrobial activity against Gram-positive and Gram-negative bacteria and actinobacteria.

Genetic validation and spectroscopic detailing of DHN-melanin extracted from an environmental fungus

Accurate characterization of melanin using analytical methodologies has proved to be difficult due to its heterogeneity, insolubility in wide pH and broad range of solvents. The present study was undertaken to characterize melanin extracted from an environmental Aspergillus fumigatus AFGRD105 by studying its genes, chemical properties and spectral data. A gene based approach to confirm the type of melanin carried out indicated the extracted melanin to be of the dihydroxynaphthalene type. On comparison with synthetic melanin, UV–Vis and IR spectra of the extracted melanin revealed characteristic peaks that can be further used for confirmation of DHN-melanin extracted from any source. Solid state ¹³C NMR spectroscopy established the presence of the hydroxyl-naphthalene moiety and validated the results obtained by genetic analysis. The correct assignment of the observed spectral frequency characteristic of functional groups can be further adapted in future works that deal with binding capacities and biomolecule systems involving melanin.

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DNA was extracted by a standardised protocol that can be adapted for environmental and clinically isolated fungi.

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The presence of genes was used to identify the type of melanin.

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Physico chemical characterization of the melanin extracted was performed.

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UV–Vis and IR spectra were used to confirm the type of melanin. Further, the chemical moieties were substantiated using ¹³C solid state NMR spectroscopy.

Differential Antifungal Activity of Human and Cryptococcal Melanins with Structural Discrepancies

Melanin is a pigment found in all biological kingdoms, and plays a key role in protection against ultraviolet radiation, oxidizing agents, and ionizing radiation damage. Melanin exerts an antimicrobial activity against bacteria, fungi, and parasites. We demonstrated an antifungal activity of synthetic and human melanin against Candida sp. The members of the Cryptococcus neoformans and C. gattii species complexes are capsulated yeasts, which cause cryptococcosis. For both species melanin is an important virulence factor. To evaluate if cryptococcal and human melanins have antifungal activity against Cryptococcus species they both were assayed for their antifungal properties and physico-chemical characters. Melanin extracts from human hair and different strains of C. neoformans (n = 4) and C. gattii (n = 4) were investigated. The following minimum inhibitory concentrations were found for different melanins against C. neoformans and C. gattii were (average/range): 13.7/(7.8–15.6) and 19.5/(15.6–31.2) μg/mL, respectively, for human melanin; 273.4/(125–>500) and 367.2/(125.5–>500) μg/mL for C. neoformans melanin and 125/(62.5–250) and 156.2/(62–250) μg/mL for C. gattii melanin. Using Scanning Electron Microscopy we observed that human melanin showed a compact conformation and cryptococcal melanins exposed an amorphous conformation. Infrared spectroscopy (FTIR) showed some differences in the signals related to C-C bonds of the aromatic ring of the melanin monomers. High Performance Liquid Chromatography established differences in the chromatograms of fungal melanins extracts in comparison with human and synthetic melanin, particularly in the retention time of the main compound of fungal melanin extracts and also in the presence of minor unknown compounds. On the other hand, MALDI-TOF-MS analysis showed slight differences in the spectra, specifically the presence of a minor intensity ion in synthetic and human melanin, as well as in some fungal melanin extracts. We conclude that human melanin is more active than the two fungal melanins against Cryptococcus. Although some physico-chemical differences were found, they do not explain the differences in the antifungal activity against Cryptococcus of human and cryptococcal melanins. More detailed studies on the structure should be considered to associate structure and antifungal activity.

Biological evaluation of 3-hydroxybenzyl alcohol, an extrolite produced by Aspergillus nidulans strain KZR-132

AIMS

The aim of the study was to purify and characterize a bioactive compound from Aspergillus nidulans strain KZR-132 and its biological evaluation.

METHODS AND RESULTS

A bioactive extolite was purified from A. nidulans strain KZR-132, and its chemical structure was elucidated as 3-hydroxylbenzyl alcohol (3-HBA) based on ¹ H and ¹³ C NMR, FT-IR and mass spectroscopic analysis. The antimicrobial efficacy of 3-HBA was established against Gram-positive, Gram-negative bacteria and different Candida strains. It also showed promising antibiofilm activity against various tested microbial strains. Reactive oxygen species induced by 3-HBA treatment on different Candida strains killed most of the cells and showed necrotic effect. It also exhibited dose-dependent antioxidant and anti-inflammatory activities.

CONCLUSIONS

This bioactive extrolite produced by A. nidulans isolated from a niche habitat was demonstrated to possess significant biotechnological and pharmacological potential since it exhibited broad-spectrum antimicrobial and antibiofilm activities which are reported for the first time.

SIGNIFICANCE AND IMPACT OF THE STUDY

The overall study demonstrates that 3-HBA produced by A. nidulansKZR-132 is a promising bioactive metabolite and possibly can function as a pharmacologically suitable broad-spectrum antimicrobial drug candidate against various dreaded human-related bacterial and fungal pathogens.

Pharmacological Properties of Melanin and its Function in Health

The biological pigment melanin is present in most of the biological systems. It manifests a host of biological and pharmacological properties. Its role as a molecule with special properties and functions affecting general health, including photoprotective and immunological action, are well recognized. Its antioxidant, anti-inflammatory, immunomodulatory, radioprotective, hepatic, gastrointestinal and hypoglycaemic benefits have only recently been recognized and studied. It is also associated with certain disorders of the nervous system. In this MiniReview, we consider the steadily increasing literature on the bioavailability and functional activity of melanin. Published literature shows that melanin may play a number of possible pharmacological effects such as protective, stimulatory, diagnostic and curative roles in human health. In this MiniReview, possible health roles and pharmacological effects are considered.

GC-MS, FTIR and Raman Analysis of Antioxidant Components of Red Pigments from Stemphylium lycopersici

Many microorganisms can generate pigments with different colours and structures during the growth process. In this study, an endophytic fungus producing red pigments was isolated from Cynanchum auriculatum Royle ex Wight tissue. PCR amplification sequencing was conducted, and phylogenetic analysis was performed on the ITS region sequences. Combined with morphological observation, the fungus was identified as Stemphylium lycopersici. The antioxidant activities of the pigments were evaluated in vitro and showed good antioxidant properties. Ultraviolet (UV), Raman, and Fourier transform infrared (FTIR) spectroscopy and gas chromatography-mass spectroscopy (GC-MS) were used to analyse the pigments' components, which were shown to contain phenolics and anthraquinones. Most of these components have not been previously reported in Stemphylium lycopersici, especially physcione. This study is the first report of Stemphylium lycopersici secondary metabolites and their potential use as red pigments and antioxidants. Further optimisation of the culture conditions of this fungal strain might permit its application for pigment production.