Scalable Biosynthesis of Melanin by the Basidiomycete Armillaria cepistipes

Expanding the application of tyrosine: engineering microbes for the production of tyrosine and its derivatives

Aromatic compounds are widely used in the fields of medicine, chemical industry, and food, with a considerable market size. Tyrosine, an aromatic amino acid, boasts not only a wide range of applications but also serves as a valuable precursor for synthesizing a diverse array of high-value aromatic compounds. Amid growing concerns over environmental and resource challenges, the adoption of green, clean, and sustainable biotechnology for producing aromatic compounds is gaining increasing recognition as a viable alternative to traditional chemical synthesis and plant extraction methods. This article provides an overview of the current status of tyrosine biomanufacturing and explores the methods for generating derivatives, including resveratrol, levodopa, p-coumaric acid, caffeic acid, zosteric acid, tyrosol, hydroxytyrosol, tanshinol, naringenin, eriodictyol, and salidroside, using tyrosine as a primary raw material. Furthermore, this review examines the current challenges and outlines future directions for microbial fermentation for the production of tyrosine and its derivatives.

Identification and functional characterization of major gene pcmfs, controlling cap color formation in Pleurotus cornucopiae

Oyster mushrooms are grown commercially worldwide, especially in many developing countries, for their easy cultivation and high biological efficiency. Cap color is an important commercial trait for oyster mushrooms. Little is known about the genetic mechanism of the cap color trait in oyster mushrooms, which limits molecular breeding for the improvement of cap color-type cultivars. In this study, an important candidate gene, pcmfs, for cap color in the oyster mushroom Pleurotus cornucopiae was identified based on the results of QTL (quantitative trait loci) mapping and comparative transcriptome analysis of our previous research. The pcmfs gene belonged to major facilitator superfamily (MFS) and was localized to the cell membrane. Expression pattern analysis and overexpression experiment demonstrated that pcmfs played an important positive role in cap color formation, with high expression levels leading to dark cap color. To our knowledge, this is the first reported gene that may be involved in the melanin transport in edible fungi. The results will enhance our understanding of the genetic basis for cap color formation in oyster mushrooms, ultimately facilitating the targeted molecular breeding of this phenotypic trait.IMPORTANCEOyster mushrooms are widely cultivated worldwide, particularly in developing countries, owing to their straightforward cultivation requirements and high biological efficiency. Cap color represents a significant commercial trait of oyster mushrooms. Despite its significance, the genetic basis of this trait remains poorly understood, limiting progress in molecular breeding to diversify cap color variants. Bridging this knowledge gap could improve the market appeal and consumer satisfaction of these cultivars by facilitating targeted breeding strategies. In our previous research, a major QTL of cap color in oyster mushroom P. cornucopiae was mapped and DEGs (differentially expressed genes) between the dark strains and white strains were identified. Based on this, the candidate gene for cap color pcmfs was further mined. The pcmfs gene, belonging to the major facilitator superfamily (MFS), is localized to the cell membrane. Expression pattern analysis and overexpression experiments have shown that pcmfs plays a significant role in cap color formation. To our knowledge, this is the first reported gene that may be involved in the melanin transport in edible fungi. The results contribute to elucidate the genetic mechanisms governing cap color formation in mushrooms, advancing targeted molecular breeding for this trait.

Characterization of melanin from the fungus Scolecobasidium Musae and its antioxidant and photoprotective properties

Melanin is a dark colored pigment produced by various living organisms. In this study, the melanin-producing fungus was isolated from a washing machine and identified as Scolecobasidium musae by 18 S rDNA analysis. Melanin production by S. musae was reported for the first time. Melanin was obtained from the dark-colored biomass produced by S. musae in submerged culture. The pigment was then purified, characterized, and identified. It was determined that purified melanin was dissolved easily in alkaline solutions but insoluble in organic solvents. Devices such as UV-Vis spectroscopy, XRD, FTIR, NMR, EPR, and elemental analysis were used to determine the chemical content and structure of the produced melanin. The melanin synthesis pathway was investigated using melanin inhibitors and by performing LC-MS analysis of the fermentation medium in which S. musae grew. It was found that the newly produced melanin from S. musae possesses antioxidant and photoprotective properties (sun protection and UV protection for Staphylococcus aureus). These results provide new possibilities for the biotechnological applications of this naturally producing melanin pigment.

Investigation of Eumelanin Biosynthesis in Gluconacetobacter tumulisoli FBFS 97: A Novel Insight into a Bacterial Melanin Producer

Acetic acid bacteria (AAB) are a group of bacteria, most of which can produce pigments. However, the mechanism of pigment production by AAB is unclear. A strain of AAB, Gluconacetobacter tumulisoli FBFS 97, which can produce a large amount of brown pigment (BP), was isolated in our previous research. In the current study, it was found that the BP yield of the FBFS 97 strain was enhanced in the presence of tyrosine, and an intermediate of melanin, L-3,4-dihydroxyphenylalanine (L-DOPA), was identified using ultra-performance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS). The structural properties of BP were analyzed by pyrolysis gas chromatography-mass spectrometry (Py-GC-MS). All these analyses suggest that BP may be eumelanin, a type of melanin. Then, the eumelanin biosynthetic pathway was investigated in the FBFS 97 strain, and three related genes with eumelanin including pheA, yfiH, and phhB in its genome were found and knocked out, respectively. The results showed that eumelanin production increased 1.3-fold in the pheA deletion mutant compared to the wild-type FBFS 97 strain, but when either yfiH or phhB was knocked out, the eumelanin production in the mutants was the same as that in the wild-type FBFS 97 strain. Finally, a possible biosynthetic pathway for eumelanin in the FBFS 97 strain is proposed.

Neuroprotective effects of melanins and melanin derivatives from Calvatia Craniiformis and Xylaria plebeja against Parkinsonian toxins

Fungal melanins have remarkable bioactivities, but their practical applications are limited, partly due to their hydrophobic nature. Melanin modification with amino acids was reported to improve their water solubility. This research aimed to extract, and modify the melanins from Calvatia craniiformis and Xylaria plebeja with arginine, and to evaluate their neuroprotective effects against Parkinsonian toxins. MTT assay showed that all melanins and melanin derivatives could protect SH-SY5Y neuroblastoma cells from 1 mM H2O2. Xylaria plebeja melanin and melanin derivative at 100 µg/mL increased the cell viability about 16.0% compared to the negative control, whereas C. craniiformis melanin and its modified form enhanced the cell viability by 18.4% and 8.3%, respectively and that of the positive control (20 µM resveratrol) was 35.5%. Regarding neuroprotective effects against MPTP, the positive control, C. craniiformis melanin, and modified melanin increased the cell viability with approximately 5.0%, but that of X. plebeja melanin and modified melanin were 13.0%. Both melanins and melanin derivatives from C. craniiformis and X. plebeja showed significant neuroprotective effects against H2O2. However, only X. plebeja melanin and modified melanin displayed significant neuroprotective effects against MPTP and therefore they would be potential materials for follow-up research in Parkinson's disease prevention.

Suppression of mycotoxins production and efficient chelation of heavy metals using natural melanin originated from Aspergillus flavus and Aspergillus carbonarius

BACKGROUND

This study employed melanin synthesized by Aspergillus flavus and Aspergillus carbonarius to inhibit the production of mycotoxins and bioremediation of heavy metals (HMs).

METHODS

First, twenty fungal isolates were obtained from soil samples, and were evaluated to produce melanin. The melanin of the most potent producers has undergone several confirmatory experiments, including, Dihydroxyphenylalanine (DOPA)-inhibitor-kojic acid pathway detection, High-performance liquid chromatography (HPLC), Fourier-transform infrared (FTIR) and Nuclear magnetic resonance (NMR). Additionally, the melanin production culture conditions were optimized. The antioxidant activity of melanin was detected with 1,1-Diphenyl-2-picrylhydrazyl (DPPH). HPLC was used to measure the mycotoxins produced in culture media supplemented with melanin. Molecular docking study investigated molecular interactions between melanin and mycotoxins through in silico approaches. FTIR and Energy-dispersive X-ray spectroscopy (EDX) were utilized to determine the percentage of melanin-chelated HMs, and an atomic absorption spectrophotometer (AAS) was used to detect HMs removal efficiency.

RESULTS

The melanin-enriched medium (0.3% and 0.4%) exhibited complete inhibition of aflatoxin B1 (AF-B1) by A. flavus and ochratoxin A (OTA) by A. carbonarius, respectively. Furthermore, melanin showed effective HM removal efficiency, increasing with melanin concentration. The removal efficiency of Cd+2 and Cr+6 by 1 mg/mL melanin was 49% and 63%, respectively. When the concentration of melanin was increased to 15 mg/mL, the removal efficiency of Cd+2 and Cr+2 increased to 60% and 77%, respectively.

CONCLUSION

The study exhibited a natural approach for melanin production, using melanin as a heavy metal-chelating agent and capability to inhibit the production of aflatoxin B1 and ochratoxin A. Further, the study provides significant evidence regarding the bioremediation pipeline, for melanin production through biotechnological processes by filamentous fungi.

Melanin in fungi: advances in structure, biosynthesis, regulation, and metabolic engineering

Fungi can synthesize a diverse range of melanins with appropriate physicochemical and biological characteristics for numerous applications in health, environmental protection, energy, and industry. Gaining deeper insights into the chemical structures, biosynthetic pathways, and regulatory mechanisms of fungal melanin would establish a basis for metabolic engineering approaches, aimed at enhancing production efficiency and creating custom-designed melanin with desirable material properties. Due to growing interest in their beneficial effects and applications, research on the structure, biosynthesis, and regulation of fungal melanin has significantly advanced. This review highlighted recent progress in fungal melanin production and applications, concentrating on structure, biosynthesis, and regulatory networks, and suggested how an improved understanding of melanin biosynthesis could enable efficient production for future applications.

Biosorption of halophilic fungal melanized membrane - PUR/melanin polymer for heavy metal detoxification with electrospinning technology

Eradication of heavy metal pollution has become the prime priority over the conservation of water resources in the upcoming era. Herein, the study involved the halophilic fungal melanin from Curvularia lunata showed a promising biosorbent for the removal of toxic heavy metals which shows eco-friendly, cost-effective, high stability, and adsorbent efficiency. Polyurethane blended with fungal melanin polymers, makes polymeric nanofibrous membranes through electrospinning techniques. BET isotherms revealed the raw fungal melanin holds a surface area of 3.54 m2/g exhibiting type IV isotherms. BJH results in a total pore volume of 5.79 cc/g with a pore diameter of 6.54 ± 1 nm for pores smaller than 4544.8 Å. Exhibits Eumelanin properties were characterized by FE - SEM and FTIR functional elements. ICPMS confirmed the metal adsorption proficiency on both raw and melanized membranes before and after treatments. Over 17 heavy metals, Ni2+ were adsorbed with 100% efficiency by raw melanin alone with 42.48 µg/L of Ni2+ concentration in the water sample, whereas, Cu2+, Zn2+, Co2+, Cr2+, Pb2+, Mn2+, Al3+, Mo6+, Sb3+, Ba2+, Fe2+, and Mg2+ stands next with 99%. In this study, gentle/simple application of raw fungal melanin (without PUR tailored) can detoxify the maximum concentration of heavy metals present in the water bodies which are further used for irrigation and even drinking purposes. This mycoremediation approach can be easily adapted to industrial production than other high-performance membrane materials with minimal process modification, making it a promising strategy for improving the adsorption properties used in various applications after still furthermore investigation.

Inkjet-Printed Bio-Based Melanin Composite Humidity Sensor for Sustainable Electronics

A lack of sustainability in the design of electronic components contributes to the current challenges of electronic waste and material sourcing. Common materials for electronics are prone to environmental, economic, and ethical problems in their sourcing, and at the end of their life often contribute to toxic and nonrecyclable waste. This study investigates the inkjet printing of flexible humidity sensors and includes biosourced and biodegradable materials to improve the sustainability of the process. Humidity sensors are useful tools for monitoring atmospheric conditions in various fields. Here, an aqueous dispersion of black soldier fly melanin was optimized for printing with a cosolvent and deposited onto interdigitated silver electrodes on flexible substrates. Impedance spectroscopy demonstrated that adding choline chloride increased the ion concentration and AC conductivity by more than 3 orders of magnitude, resulting in a significant improvement in sensing performance and reduced hysteresis. The devices exhibit fast detection (0.8 ± 0.5 s) and recovery times (0.8 ± 0.3 s), with a 170 ± 40-fold decrease in impedance for relative humidity changes from 30% to 90%. This factor is lowered upon prolonged exposure to high humidity in tests over 72 h during which a stable operation is reached. The low embodied energy of the sensor, achieved through material-efficient deposition and the use of waste management byproducts, enhances its sustainability. In addition, approaches for reusability and degradability are presented, rendering the sensor suitable for wearable or agricultural applications.

Ozone-Induced Rapid and Green Synthesis of Polydopamine Coatings with High Uniformity and Enhanced Stability

The development of green, controllable, and simplified pathways for rapid dopamine polymerization holds significant importance in the field of polydopamine (PDA) surface chemistry. In this study, a green strategy is successfully devised to accelerate and control the polymerization of dopamine through the introduction of ozone (O3 ). The findings reveal that ozone serves as an eco-friendly trigger, significantly accelerating the dopamine polymerization process across a broad pH range, spanning from 4.0 to 10.0. Notably, the deposition rate of PDA coatings on a silicon wafer reaches an impressive value of ≈64.8 nm h-1 (pH 8.5), which is 30 times higher than that of traditional air-assisted PDA and comparable to the fastest reported method. Furthermore, ozone exhibits the ability to accelerate dopamine polymerization even under low temperatures. It also enables control over the inhibition-initiation of the polymerization process by regulating the "ON/OFF" mode of the ozone gas. Moreover, the ozone-induced PDA coatings demonstrate exceptional characteristics, including high homogeneity, good hydrophilicity, and remarkable chemical and mechanical stability. Additionally, the ozone-induced PDA coatings can be rapidly and effectively deposited onto a wide range of substrates, particularly those that are adhesion-resistant, such as polytetrafluoroethylene (PTFE).

Efficient Production of Melanin by Aureobasidium Melanogenum Using a Simplified Medium and pH-Controlled Fermentation Strategy with the Cell Morphology Analysis

Natural melanin is a biopolymer with wide application prospects in medicine, food, cosmetics, environmental protection, agriculture, and so on. Microbial fermentation is an important and effective way to produce melanin. In this study, Aureobasidium melanogenum, known as black yeast with cellular pleomorphism, was used for the production of melanin. Based on the characteristic of A. melanogenum secreting melanin under oligotrophic stress, a simple medium containing only glucose, MgSO4·7H2O, and KCl was constructed for the production of melanin. The melanin titer of 6.64 ± 0.22 g/L was obtained after 20 days of fermentation without pH control. The cell morphological changes of A. melanogenum during the production of melanin were recorded, and the results showed that chlamydospore might be the most favorable cell morphology for melanin synthesis. Then, different fermentation strategies with cell morphology analysis were developed to further improve the production of melanin in a 5-L fermenter. Results showed that the maximum titer of melanin reached 18.50 g/L by using the fermentation strategy integrating pH control, ammonium salt addition, and H2O2 stimulation, which increased by 178.6% than that of the strategy without pH control. Furthermore, the melanin obtained from the fermentation broth was characterized as eumelanin containing an indole structure. This study provided a potentially feasible fermentation strategy for the industrial production of melanin.

Melanin Synthesized by the Endophytic Aureobasidium Pullulans AKW: A Multifaceted Biomolecule with Antioxidant, Wound Healing, and Selective Anti-Cancer Activity

INTRODUCTION

This study explores the potential of the endophytic fungus Aureobasidium pullulans AKW for melanin production and its anticancer activity.

METHOD

We report a significant achievement: A. pullulans AKW synthesized 4.89 g/l of melanin in a simple fermentation medium devoid of tyrosine, a precursor typically required for melanin biosynthesis. This suggests a potentially novel pathway for melanin production compared to previous studies relying on complex media and tyrosine. Furthermore, the isolated and characterized melanin exhibited promising selectivity as an anti-cancer agent. It triggered apoptosis in A431 cancer cells, demonstrating some selectivity compared to normal cells. This selectivity was confirmed by IC50 values and further supported by gene expression changes in A431 cells. Melanin treatment downregulated the anti-apoptotic Bcl2 gene while upregulating pro-apoptotic Bax and p53 genes, indicating its ability to induce programmed cell death in cancer cells.

RESULT

Our results demonstrate that A. pullulans AKW-derived melanin exhibits cytotoxic effects against A431, HEPG2, and MCF7 cell lines. Interestingly, the present fungal strain synthesized melanin in a simple medium without requiring precursors.

CONCLUSION

The selective activity of the current melanin towards cancer cells, its ability to induce apoptosis, and its relatively low toxicity towards normal cells warrant further investigation for its development as a novel therapeutic option.

A Comparative Study of Cr(VI) Sorption by Aureobasidium pullulans AKW Biomass and Its Extracellular Melanin: Complementary Modeling with Equilibrium Isotherms, Kinetic Studies, and Decision Tree Modeling

Melanin as a natural polymer is found in all living organisms, and plays an important role in protecting the body from harmful UV rays from the sun. The efficiency of fungal biomass (Aureobasidium pullulans) and its extracellular melanin as Cr(VI) biosorbents was comparatively considered. The efficiency of Cr(VI) biosorption by the two sorbents used was augmented up to 240 min. The maximum sorption capacities were 485.747 (fungus biomass) and 595.974 (melanin) mg/g. The practical data were merely fitted to both Langmuir and Freundlich isotherms. The kinetics of the biosorption process obeyed the pseudo-first-order. Melanin was superior in Cr(VI) sorption than fungal biomass. Furthermore, four independent variables (contact time, initial concentration of Cr(VI), biosorbent dosage, and pH,) were modeled by the two decision trees (DTs). Conversely, to equilibrium isotherms and kinetic studies, DT of fungal biomass had lower errors compared to DT of melanin. Lately, the DTs improved the efficacy of the Cr(VI) removal process, thus introducing complementary and alternative solutions to equilibrium isotherms and kinetic studies. The Cr(VI) biosorption onto the biosorbents was confirmed and elucidated through FTIR, SEM, and EDX investigations. Conclusively, this is the first report study attaining the biosorption of Cr(VI) by biomass of A. pullulans and its extracellular melanin among equilibrium isotherms, kinetic study, and algorithmic decision tree modeling.

Rapid, high-titer biosynthesis of melanin using the marine bacterium Vibrio natriegens

Melanin is one of the most abundant natural biomolecules on Earth. These macromolecular biopolymers display several unique physical and chemical properties and have garnered interest as biomaterials for various commercial and industrial applications. To this end, extensive research has gone into refining methods for the synthesis and extraction of melanin from natural and recombinant sources. In this study, we developed and refined a procedure using a recombinant microbial system for the biosynthesis of melanin using the tyrosinase enzyme Tyr1 and tyrosine as a substrate. Using the emergent microbial chassis organisms Vibrio natriegens, we achieved maximal yields of 7.57 g/L, and one of the highest reported volumetric productivities of 473 mg L-1 h-1 with 100% conversion rates in an optimized, minimally defined medium. Additionally, we identified and investigated the use of a native copper responsive promoter in V. natriegens for stringent regulation of heterologous protein expression as a cost effective alternative to traditional IPTG-based induction. This research represents a promising advancement towards a green, rapid, and economical alternative for the biomanufacture of 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.

Genetic and Environmental Factors Influencing the Production of Select Fungal Colorants: Challenges and Opportunities in Industrial Applications

Natural colorants, mostly of plant and fungal origins, offer advantages over chemically synthetic colorants in terms of alleviating environmental pollution and promoting human health. The market value of natural colorants has been increasing significantly across the globe. Due to the ease of artificially culturing most fungi in the laboratory and in industrial settings, fungi have emerged as the organisms of choice for producing many natural colorants. Indeed, there is a wide variety of colorful fungi and a diversity in the structure and bioactivity of fungal colorants. Such broad diversities have spurred significant research efforts in fungi to search for natural alternatives to synthetic colorants. Here, we review recent research on the genetic and environmental factors influencing the production of three major types of natural fungal colorants: carotenoids, melanins, and polyketide-derived colorants. We highlight how molecular genetic studies and environmental condition manipulations are helping to overcome some of the challenges associated with value-added and large-scale productions of these colorants. We finish by discussing potential future trends, including synthetic biology approaches, in the commercial production of fungal colorants.

Genome Sequencing and Analysis Reveal Potential High-Valued Metabolites Synthesized by Lasiodiplodia iranensis DWH-2

Lasiodiplodia sp. is a typical opportunistic plant pathogen, which can also be classified as an endophytic fungus. In this study, the genome of a jasmonic-acid-producing Lasiodiplodia iranensis DWH-2 was sequenced and analyzed to understand its application value. The results showed that the L. iranensis DWH-2 genome was 43.01 Mb in size with a GC content of 54.82%. A total of 11,224 coding genes were predicted, among which 4776 genes were annotated based on Gene Ontology. Furthermore, the core genes involved in the pathogenicity of the genus Lasiodiplodia were determined for the first time based on pathogen-host interactions. Eight Carbohydrate-Active enzymes (CAZymes) genes related to 1,3-β-glucan synthesis were annotated based on the CAZy database and three relatively complete known biosynthetic gene clusters were identified based on the Antibiotics and Secondary Metabolites Analysis Shell database, which were associated with the synthesis of 1,3,6,8-tetrahydroxynaphthalene, dimethylcoprogen, and (R)-melanin. Moreover, eight genes associated with jasmonic acid synthesis were detected in pathways related to lipid metabolism. These findings fill the gap in the genomic data of high jasmonate-producing strains.

Fungi as a source of eumelanin: current understanding and prospects

Melanins represent a diverse collection of pigments with a variety of structures and functions. One class of melanin, eumelanin, is recognizable to most as the source of the dark black color found in cephalopod ink. Sepia officinalis is the most well-known and sought-after source of non-synthetic eumelanin, but its harvest is limited by the availability of cuttlefish, and its extraction from an animal source brings rise to ethical concerns. In recent years, these limitations have become more pressing as more applications for eumelanin are developed-particularly in medicine and electronics. This surge in interest in the applications of eumelanin has also fueled a rise in the interest of alternative, bio-catalyzed production methods. Many culinarily-utilized fungi are ideal candidates in this production scheme, as examples exist which have been shown to produce eumelanin, their growth at large scales is well understood, and they can be cultivated on recaptured waste streams. However, much of the current research on the fungal production of eumelanin focuses on pathogenic fungi and eumelanin's role in virulence. In this paper, we will review the potential for culinary fungi to produce eumelanin and provide suggestions for new research areas that would be most impactful in the search for improved fungal eumelanin producers.

Kinetic study of polydopamine sphere synthesis using TRIS: relationship between synthesis conditions and final properties

The synthesis and characterization of polydopamine (PDA) using dopamine (DA) as the monomer and (hydroxymethyl)aminomethane (TRIS) as the oxidant is studied. The effect of temperature and TRIS concentration on the kinetics of dopamine polymerization is evaluated, and the kinetic parameters are also calculated. Three TRIS concentrations are used to assess their effect on DA polymerization kinetics. The reaction at 1.5 mmol of TRIS shows a sustained increase of the rate constant with temperature from 2.38 × 10^-4 to 5.10 × 10^-4 when the temperature is increased from 25 to 55 °C; however, not all reactions follow an Arrhenius law. In addition, the correlation between the synthesis parameters and morphological, structural, and thermal properties of polydopamine is established. The morphology of the PDA particles is evaluated by Scanning Electron Microscopy (SEM), the relationships between the diameter, distribution size, and the rate constant. Thermal characterization by Differential Scanning Calorimetry (DSC) shows an endothermic transition around 130 °C associated with the melting of PDA's regular structure. It is supported by structural studies, such as infrared and Raman spectroscopy and X-ray Diffraction (XRD), by observing a broad peak at 23.1° (2θ) that fits with a graphitic-like structure of PDA.

Production of Satratoxin G and H Is Tightly Linked to Sporulation in Stachybotrys chartarum

Stachybotrys chartarum is a toxigenic fungus that is frequently isolated from damp building materials or improperly stored forage. Macrocyclic trichothecenes and in particular satratoxins are the most potent mycotoxins known to be produced by this fungus. Exposure of humans or animals to these secondary metabolites can be associated with severe health problems. To assess the pathogenic potential of S. chartarum isolates, it is essential to cultivate them under conditions that reliably promote toxin production. Potato dextrose agar (PDA) was reported to be the optimal nutrition medium for satratoxin production. In this study, the growth of S. chartarum genotype S strains on PDA from two manufacturers led to divergent results, namely, well-grown and sporulating cultures with high satratoxin concentrations (20.8 ± 0.4 µg/cm2) versus cultures with sparse sporulation and low satratoxin production (0.3 ± 0.1 µg/cm2). This finding is important for any attempt to identify toxigenic S. chartarum isolates. Further experiments performed with the two media provided strong evidence for a link between satratoxin production and sporulation. A comparison of three-point and one-point cultures grown on the two types of PDA, furthermore, demonstrated an inter-colony communication that influences both sporulation and mycotoxin production of S. chartarum genotype S strains.

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.

Isolation and identification of pigments from oyster mushrooms with black, yellow and pink caps

The genus Pleurotus, namely oyster mushroom, is widely cultivated and consumed worldwide. Cap color is an important commercial trait for oyster mushroom. Diverse color is determined by various pigment constituents. However, the pigments of oyster mushrooms are still ambiguous. In this study, we extracted and identified pigments of oyster mushroom species with black, yellow and pink cap color. The extracted pigments appearing the three color types correspondingly to the cap color, which were all identified as melanin using a panel of spectroscopic and physical/imaging techniques. Nevertheless, HPLC and elemental analysis indicated that the melanin in oyster mushrooms was actually a mixture of eumelanin and phaeomelanin. Differences in the quantities and relative proportions of eumelanin and phaeomelanin resulted in the color variation in oyster mushroom caps. Electron microscopy studies showed that the melanin units are likely located in the cell wall, as reported in other fungi. The pigments in oyster mushrooms with three different cap color were extracted and identified for the first time in this study, which provided fundamental knowledge for future studies on the mechanism of color formation in mushrooms.

New Findings on the Biology and Ecology of the Ecuadorian Amazon Fungus Polyporus leprieurii var. yasuniensis

Polyporus leprieurii var. yasuniensis is a prolific wood-decay fungus inhabiting the forest floor of one of the most biodiverse places on earth, the Yasuní National Park in Ecuador. Basidiocarps and aerial rhizomorphs are commonly found growing on woody debris distributed along the floor of this forest ecosystem. Because of the extraordinary abundance of this fungus in the tropical rainforest, we carried out investigations to better understand the biological and ecological aspects contributing to its prolific distribution. Data on growth inhibition in paired competition studies with sixteen fungal isolates exemplifies defense mechanisms used to defend its territory, including pseudosclerotial plates and the development of a melanized rhizomorphic mat. Results of biomass loss on eleven types of tropical wood in microcosm experiments demonstrated the broad decay capacity of the fungus. In and ex situ observations provided information on how long rhizomorphs can prevail in highly competitive ecosystems as well as stressful conditions in the laboratory. Finally, high concentrations of metal ions occur on rhizomorphs as compared to colonized wood. Sequestration of metal ions from the environment by the melanized rhizomorphs may offer protection against competitors. The development of melanized rhizomorphs is key to find and colonize new substrates and resist changing environmental conditions.

Stress Dependent Biofilm Formation and Bioactive Melanin Pigment Production by a Thermophilic Bacillus Species from Chilean Hot Spring

Thermophilic bacteria able to survive extreme temperature stress are of great biotechnological interest due to their extracellular production of bioactive molecules as a part of a survival strategy, or by intracellular modifications. In the present study, thermophilic Bacillus haynesii CamB6, isolated from a Chilean hot spring, was studied for the formation of different stress response molecules. The polymeric pigment produced by the bacterial strain was characterized by different physicochemical techniques. On exposure to ranges of temperature (50–60 °C), pH (5.0–7.0), and sources of nitrogen and carbon (1–5 g·L⁻¹), the bacteria responded with a biofilm network formation in a hydrophobic polystyrene surface. Biofilm formation under fed-batch conditions was also statistically validated. The bacteria showed a planktonic pellicle network formation in the presence of induced hypoxia and salinity stress (19.45 g·L⁻¹) under static conditions. Salinity stress also resulted in the intracellular response of brown pigment production. The pigment was structurally and functionally characterized by UV-Vis absorbance and the presence of different characteristic peaks via FTIR analysis (bacterial pyomelanin fingerprints) were assessed. A high thermal stability and TGA profile indicated the brown pigment was a probable pyomelanin candidate. Micropyrolysis (Py-GC/MS) showed that isoprene, pyrrole, benzene, pyridine, and their derivatives were the major components detected. In addition, acetic acid, indole, phenol, and its derivatives were observed. The absence of sulfocompounds in the pyrolyzed products agreed with those reported in the literature for pyomelanin. The pigment surface morphology was analyzed via SEM, and the elemental composition via EDS also demonstrated the similarity of the brown pigment to that of the melanin family. The pyomelanin pigment was observed to be bioactive with promising antioxidant capacity (H₂O₂, Fe²⁺) compared to the standard antioxidant molecules. In conclusion, B. haynesii CamB6 demonstrated the formation of several biomolecules as a stress response mechanism that is bioactive, showing its probable biotechnological applications in future.

Isolation and Characterization of Allomelanin from Pathogenic Black Knot Fungus-a Sustainable Source of Melanin

Melanin, a widespread pigment found in many taxa, is widely recognized for its high refractive index, ultraviolet (UV) protection, radical quenching ability, metal binding, and many other unique properties. The aforementioned characteristic traits make melanin a potential candidate for biomedical, separation, structural coloration, and space applications. However, the commercially available natural (sepia) and synthetic melanin are very expensive, limiting their use in various applications. Additionally, eumelanin has been the primary focus in most of these studies. In the present study, we demonstrate that melanin can be extracted from the pathogenic black knot fungus Apiosporina morbosa with a yield of ∼10% using the acid-base extraction method. The extracted melanin shows irregular morphology. Chemical characterization using X-ray photoelectron spectroscopy, infrared spectroscopy, and solid-state nuclear magnetic resonance spectroscopy reveals that the melanin derived from black knots is the less explored nitrogen-free allomelanin. Additionally, the extracted melanin shows broadband UV absorption typical of other types of melanin. Because of the wide availability and low cost of black knots and the invasive nature of the fungus, black knots can serve as an alternative green source for obtaining allomelanin at a low cost, which could stimulate its use as an UV light absorber and antioxidant in cosmetics and packaging industries.

Bioprocess of Microbial Melanin Production and Isolation

Melanin is one of the most abundant pigments found in the biosphere. Owing to its high biocompatibility and diverse biological activities, it has been widely applied as a functional biomaterial in the cosmetic, pharmaceutical, biopolymer, and environmental fields. In this study, the production of melanin was comprehensively reviewed concerning bioconversion and isolation processes. First, several melanogenic microbes, including fungi and bacteria, were summarized. Melanin production was classified by host and melanin type and was analyzed by titers in g/L in addition to reaction conditions, including pH and temperature. The production was further interpreted using a space-time yields chart, which showed two distinct classifications in productivity, and reaction conditions were analyzed using a pH-temperature-titer chart. Next, the extraction process was summarized by crude and pure melanin preparation procedures, and the extraction yields were highlighted. Finally, the recent applications of melanin were briefly summarized, and prospects for further application and development in industrial applications were suggested.

Melanized-Cationic Cellulose Nanofiber Foams for Bioinspired Removal of Cationic Dyes

In recent years, water pollution has developed into a severe environmental and public health problem due to rapid urbanization and industrialization, especially in some developing countries. Finding solutions to tackle water pollution is urgently required and is of global importance. Currently, a range of water treatment methods are available; however, a water remediation process that is simple, inexpensive, eco-friendly, and effective for the removal of pollutants down to ppm/ppb concentrations has long been sought after. Herein, we describe a novel approach using fungal melanin for developing melanized-cationic cellulose nanofiber (melanized-C-CNF) foams that can successfully remove pollutants in water systems. The foam can be recycled several times while retaining its adsorption/desorption property, indicating high practicability for adsorbing the cationic dye crystal violet. This work highlights the opportunity to combine both the advanced features of sustainable polymers such as cellulose and the unique properties of fungal melanin to manufacture biohybrid composites for water purification.

Fungal Melanins and Applications in Healthcare, Bioremediation and Industry

Melanin is a complex multifunctional pigment found in all kingdoms of life, including fungi. The complex chemical structure of fungal melanins, yet to be fully elucidated, lends them multiple unique functions ranging from radioprotection and antioxidant activity to heavy metal chelation and organic compound absorption. Given their many biological functions, fungal melanins present many possibilities as natural compounds that could be exploited for human use. This review summarizes the current discourse and attempts to apply fungal melanin to enhance human health, remove pollutants from ecosystems, and streamline industrial processes. While the potential applications of fungal melanins are often discussed in the scientific community, they are successfully executed less often. Some of the challenges in the applications of fungal melanin to technology include the knowledge gap about their detailed structure, difficulties in isolating melanotic fungi, challenges in extracting melanin from isolated species, and the pathogenicity concerns that accompany working with live melanotic fungi. With proper acknowledgment of these challenges, fungal melanin holds great potential for societal benefit in the coming years.

Utilization of extracellular fungal melanin as an eco-friendly biosorbent for treatment of metal-contaminated effluents

Fungal melanins have been considered as potential biosorbents due to their metal-binding properties, stability, and scalability. Previous studies established scalable fungal melanin production methods with promising strains, however, their applicability for metal-contaminated effluents treatment has not been sufficiently reported. Herein, melanin pigment derived from Amorphotheca resinae was produced and characterized using microscopy and spectroscopy techniques. Adsorptive properties towards Cu(II), Pb(II), Cd(II), and Zn(II) were evaluated using batch tests. Melanin pigment was composed of aggregates of nanosized particles with indole-based constituents. Adsorption capacities increased with the pH of solution, especially at pH > 4.0. Maximum binding capacities of Cu(II), Pb(II), Cd(II), and Zn(II) on melanin were 69.18, 103.23, 24.31, and 13.57 mg/g, respectively. The competitive adsorption experiments elucidated affinity as Cu(II)>Pb(II)≫Cd(II)>Zn(II). Adsorption time generally required <2.5 h to reach equilibrium; the pseudo-second-order kinetic model well described the kinetics. Chelating ability of free radicals in pigment was considered as a possible mechanism for adsorption. Initial adsorption capacities remained almost intact even after 5 consecutive adsorption-desorption cycles. Complete removal of Cu(II), Pb(II), and Cd(II) from metal-contaminated effluent was confirmed. Consequently, melanin pigment derived from A. resinae can be used as a biosorbent suitable for the treatment of metal-contaminated aqueous solutions.

Fungal melanin as a biocompatible broad-spectrum sunscreen with high antioxidant activity

Melanin is considered a bio-inspired dermo-cosmetic component due to its high UV absorption and antioxidant activity. Among various melanin sources, fungal melanin is a promising candidate for sunscreen because of its sustainability and scalability; however, quantitative assessment of its function has not yet been sufficiently explored. In this study, melanin samples derived from Amorphotheca resinae were prepared, followed by the evaluation of their sunscreen performance, antioxidant activity, and cytotoxicity. Melanin-blended cream was prepared by blending a melanin suspension and a pure cream. The cream showed an in vitro sun protection factor value of 2.5 when the pigment content was 5%. The cream showed a critical wavelength of approximately 388 nm and a UVA/UVB ratio of more than 0.81, satisfying the broad-spectrum sunscreen requirement. Oxygen radical absorbance capacity assays indicated that fungal melanin had antioxidant activity similar to ascorbic acid but higher than reduced glutathione. Fungal melanin had no statistically significant cytotoxicity to human keratinocyte cell lines until 72 h of exposure, even at a concentration of 4 mg mL-1. Consequently, melanin pigment can be used as a biocompatible broad-spectrum sunscreen with high antioxidant activity and as a practical alternative in dermo-cosmetic formulations.

Biodegradation of bio-sourced and synthetic organic electronic materials towards green organic electronics

Ubiquitous use of electronic devices has led to an unprecedented increase in related waste as well as the worldwide depletion of reserves of key chemical elements required in their manufacturing. The use of biodegradable and abundant organic (carbon-based) electronic materials can contribute to alleviate the environmental impact of the electronic industry. The pigment eumelanin is a bio-sourced candidate for environmentally benign (green) organic electronics. The biodegradation of eumelanin extracted from cuttlefish ink is studied both at 25 °C (mesophilic conditions) and 58 °C (thermophilic conditions) following ASTM D5338 and comparatively evaluated with the biodegradation of two synthetic organic electronic materials, namely copper (II) phthalocyanine (Cu-Pc) and polyphenylene sulfide (PPS). Eumelanin biodegradation reaches 4.1% (25 °C) in 97 days and 37% (58 °C) in 98 days, and residual material is found to be without phytotoxic effects. The two synthetic materials, Cu-Pc and PPS, do not biodegrade; Cu-Pc brings about the inhibition of microbial respiration in the compost. PPS appears to be potentially phytotoxic. Finally, some considerations regarding the biodegradation test as well as the disambiguation of "biodegradability" and "bioresorbability" are highlighted.

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.

Genomic Analysis and Assessment of Melanin Synthesis in Amorphotheca resinae KUC3009

This study reports the draft genome of Amorphotheca resinae KUC30009, a fungal isolate with promising industrial-scale melanin production potential. The mechanisms for melanin or melanin-related pigment formation of this strain were examined through bioinformatic and biochemical strategies. The 30.11 Mb genome of A. resinae contains 9638 predicted genes. Genomic-based discovery analyses identified 14 biosynthetic gene clusters (BGCs) associated with secondary metabolite production. Moreover, genes encoding a specific type 1 polyketide synthase and 4-hydroxynaphthalene reductase were identified and predicted to produce intermediate metabolites of dihydroxy naphthalene (DHN)-melanin biosynthesis pathway, but not to DHN-melanin. These findings were further supported by the detection of increased flaviolin concentrations in mycelia and almost unchanged morphologies of the culture grown with tricyclazole. Apart from this, the formation of melanin in the culture filtrate appeared to depend on the laccase-like activity of multi-copper oxidases. Simultaneously, concentrations of nitrogen-containing sources decreased when the melanin formed in the media. Interestingly, melanin formation in the culture fluid was proportional to laccase-like activity. Based on these findings, we proposed novel strategies for the enhancement of melanin production in culture filtrates. Therefore, our study established a theoretical and methodological basis for synthesizing pigments from fungal isolates using genomic- and biochemical-based approaches.

Colors of life: a review on fungal pigments

Colorants find social and commercial applications in cosmetics, food, pharmaceuticals, textiles, and other industrial sectors. Among the available options, chemically synthesized colorants are popular due to their low-cost and flexible production modes, but health and environmental concerns have encouraged the valorization of biopigments that are natural and ecofriendly. Among natural biopigment producers, microorganisms are noteworthy for their all-seasonal production of stable and low-cost pigments with high-yield titers. Fungi are paramount sources of natural pigments. They occupy diverse ecological niches with adaptive metabolisms and biocatalytic pathways, making them entities with an industrial interest. Industrially important biopigments like carotenoids, melanins, riboflavins, azaphilones, and quinones produced by filamentous fungi are described within the context of this review. Most recent information about fungal pigment characteristics, biochemical production routes and pathways, potential applications, limitations, and future research perspectives are described.

Microbial Production of Melanin Pigments from Caffeic Acid and L-tyrosine Using Streptomyces glaucescens and FCS-ECH-Expressing Escherichia coli

In this study, synthetic allomelanin was prepared from wild-type Streptomyces glaucescens and recombinant Escherichia coli BL21(DE3) strains. S. glaucescens could produce 125.25 ± 6.01 mg/L of melanin with a supply of 5 mM caffeic acid within 144 h. The ABTS radical scavenging capacity of S. glaucescens melanin was determined to be approximately 7.89 mg/mL of IC50 value, which was comparable to L-tyrosine-based eumelanin. The isolated melanin was used in cotton fabric dyeing, and the effect of copper ions, laccase enzyme treatment, and the dyeing cycle on dyeing performance was investigated. Interestingly, dyeing fastness was greatly improved upon treatment with the laccase enzyme during the cotton dyeing process. Besides, the supply of C5-diamine, which was reported to lead to more complex crosslinking between melanin units, to caffeic acid-based melanin synthesis was also investigated for higher production and novel functionalities. To facilitate the supply of caffeic acid and C5-diamine, E. coli strains expressing each or combinations of tyrosine ammonia lyase/p-coumarate 3-hydroxylase, feruloyl-CoA synthetase/enoyl-CoA hydratase/aldolase, and tyrosinase/lysine decarboxylase enzymes were prepared and investigated for their eumelanin, C5-diamine, and allomelanin production from L-tyrosine and L-lysine, respectively. Finally, H-NMR, FT-IR, and MALDI-TOF analysis of the synthetic melanin pigments were attempted to obtain the chemical information.

Melanins as Sustainable Resources for Advanced Biotechnological Applications

Melanins are a class of biopolymers that are widespread in nature and have diverse origins, chemical compositions, and functions. Their chemical, electrical, optical, and paramagnetic properties offer opportunities for applications in materials science, particularly for medical and technical uses. This review focuses on the application of analytical techniques to study melanins in multidisciplinary contexts with a view to their use as sustainable resources for advanced biotechnological applications, and how these may facilitate the achievement of the United Nations Sustainable Development Goals.

Mind the mushroom: natural product biosynthetic genes and enzymes of Basidiomycota

Covering: up to September 2020 Mushroom-forming fungi of the division Basidiomycota have traditionally been recognised as prolific producers of structurally diverse and often bioactive secondary metabolites, using the methods of chemistry for research. Over the past decade, -omics technologies were applied on these fungi, and sophisticated heterologous gene expression platforms emerged, which have boosted research into the genetic and biochemical basis of the biosyntheses. This review provides an overview on experimentally confirmed natural product biosyntheses of basidiomycete polyketides, amino acid-derived products, terpenoids, and volatiles. We also present challenges and solutions particular to natural product research with these fungi. 222 references are cited.

Bio-synthesis of food additives and colorants-a growing trend in future food

Food additives and colorants are extensively used in the food industry to improve food quality and safety during processing, storage and packing. Sourcing of these molecules is predominately through three means: extraction from natural sources, chemical synthesis, and bio-production, with the first two being the most utilized. However, growing demands for sustainability, safety and "natural" products have renewed interest in using bio-based production methods. Likewise, the move to more cultured foods and meat alternatives requires the production of new additives and colorants. The production of bio-based food additives and colorants is an interdisciplinary research endeavor and represents a growing trend in future food. To highlight the potential of microbial hosts for food additive and colorant production, we focus on current advances for example molecules based on their utilization stage and bio-production yield as follows: (I) approved and industrially produced with high titers; (II) approved and produced with decent titers (in the g/L range), but requiring further engineering to reduce production costs; (III) approved and produced with very early stage titers (in the mg/L range); and (IV) new/potential candidates that have not been approved but can be sourced through microbes. Promising approaches, as well as current challenges and future directions will also be thoroughly discussed for the bioproduction of these food additives and colorants.

Comparison of physicochemical and biochemical properties of natural and arginine-modified melanin from medicinal mushroom Ganoderma lucidum

Melanin is a hydrophobic biomolecule produced widely in fungi. Compared with other fungi, health benefits have been associated with medicinal mushrooms, which may provide an excellent source of natural melanin. Nevertheless, the hydrophobicity of melanin may limit its applications. Consequently, the present study was carried out on isolation of melanin from the medicinal mushroom Ganoderma lucidum (GLM) and modification with arginine to improve its solubility. The physicochemical and biochemical properties of melanin were evaluated including structural characterization, solubility, stability, antioxidant activities, and inhibitory effect on pancreatic lipase activity. Arginine-modified melanin showed better solubility, higher color value, stronger antioxidant activity, and stronger inhibitory effect on pancreatic lipase activity in vitro than GLM. In addition, both have good stability in the dark and natural light. These results opened possibilities for providing an excellent source of natural melanin in health food or food additives fields.

Microbial production of melanin and its various applications

Melanins are natural biopolymers that are known to contribute to different biological processes and to protect organisms from adverse environmental conditions. During the past decade, melanins have attracted increasing attention for their use in organic semiconductors and bioelectronics, drug delivery, photoprotection and environmental bioremediation. Although considerable advances in these fields have been achieved, real-world applications of melanins are still scarce, probably due to the limited and expensive source of natural melanin. Nevertheless, recent biotechnological advances have allowed for relatively large-scale production of microbial melanins, which could replace current commercial melanin. In this review, we first describe different melanin sources and highlight the advantages and disadvantages of each production method. Our focus is on the microbial synthesis of melanins, including the methodology and mechanism of melanin formation. Applications of microbial melanins are also discussed, and an outlook on how to push the field forward is discussed.

Production and characterization of melanin pigments derived from Amorphotheca resinae

As melanin has emerged as functional pigment with cosmetic, health and food applications, the demand for the pigments is expected to increase. However, the conventional sources (e.g. mushroom, hair, and wool) of melanin production entail pigments inside the substrates which requires the costly extraction procedures, leading to inappropriate scalable production. In this study, we screened 102 of fungal isolates for their ability to produce melanin in the supernatant and selected the only Amorphotheca resinae as a promising candidate. In the peptone yeast extract glucose broth, A. resinae produced the melanin rapidly during the autolysis phase of growth, reaching up 4.5 g/L within 14 days. Structural characterization of the purified melanin from A. resinae was carried out by using elemental analysis, electron paramagnetic resonance, ¹³C solid-state nuclear magnetic resonance spectroscopy, and pyrolysis-gas chromatography-mass spectrometry in comparison with the standard melanins. The results indicate that the structural properties of A. resinae melanin is similar to the eumelanin which has a wide range of industrial uses. For example, the purified melanin from A. resinae has the potent antioxidant activities as a result of free radical scavenging assays. Consequently, A. resinae KUC3009 can be a promising candidate for scalable production of industrially applicable melanin.

Paramagnetism and Relaxation Dynamics in Melanin Biomaterials

Spectroscopical characterization of melanins is a prior requirement for the efficient tailoring of their radical scavenging, ultraviolet-visible radiation absorption, metal chelation, and natural pigment properties. Electron paramagnetic resonance (EPR), exploiting the common persistent paramagnetism of melanins, represents the elective standard for the structural and dynamical characterization of their constituting radical species. Although melanins are mainly investigated using X-band (9.5 GHz) continuous wave (CW)-EPR, an integration with the application of Q-band (34 GHz) in CW and pulse EPR for the discrimination of melanin pigments of different compositions is presented here. The longitudinal relaxation times measured highlight faster relaxation rates for cysteinyldopa melanin, compared to those of the most common dopa melanin pigment, suggesting pulse EPR spin-lattice relaxation time measurements as a complementary tool for characterization of pigments of interest for biomimetic materials engineering.