Characterization of water-soluble dark-brown pigment from Antarctic bacterium, Lysobacter oligotrophicus

Biological activities of BY2-melanin, a plant-type eumelanin, isolated from cultured tobacco BY-2 cells

BY2-melanin, a plant eumelanin distinct from nitrogen-free plant allomelanins, was previously isolated from cultured BY-2 tobacco cells. Herein, the biological activities of BY2-melanin, including its ability to protect against ultraviolet radiation (UVR) and antioxidant activity, were investigated. Based on the survival rate of Escherichia coli, the ability of BY2-melanin to protect against UVR was three and eight times higher than that of melanins isolated from fungi and bacteria, respectively. Its antioxidant activities, determined as ferrous iron-chelating activity and reducing power, were 1.7-4.9 and 0.3-0.4 times higher than those of animal melanins, respectively. Its 2,2-diphenyl-1-picrylhydrazyl and superoxide radical scavenging activities were similar to those of mushroom melanin, whereas its hydroxyl radical scavenging activity was one-fourth of that of melanins derived from mushroom and black tea. These findings shed light on the development of a class of melanin biopolymers that can be used as a broad-spectrum sunscreen with antioxidant activity.

Isolation and Characterization of an Antioxidant Aryl Polyene Pigment from Antarctic Bacterium Lysobacter sp. A03

Lysobacter is known as a bacterial genus with biotechnological potential, producing an array of enzymes, antimicrobial metabolites, and bioactive antioxidant compounds, including aryl polyene (APE) pigments that have been described as protecting substances against photooxidative damage and lipid peroxidation. In this study, the pigment extracted from keratinolytic Lysobacter sp. A03 isolated from Antarctic environment was characterized. The results of KOH test, UV-vis spectroscopy, CIELAB color system, 1H-NMR, and FTIR-ATR spectroscopy suggest the pigment is a yellow xanthomonadin-like pigment. The in vitro antioxidant activity of the pigment was confirmed by the scavenging of ABTS and DPPH radicals. In silico analysis of the genome through antiSMASH software was also performed and the secondary metabolite gene clusters for APE and resorcinol synthesis were identified, suggesting that proteins responsible for the pigment biosynthesis are encoded in Lysobacter A03 genome.

Biocompatible melanin from the marine black yeast Hortaea werneckii R23 with antioxidant and photoprotection property

Pigments from diverse sources have a great deal of interest due to its multifaceted applications. Hence, this study reports the physicochemical and functional characterization of the black pigment melanin from the marine black yeast Hortaea werneckii R23. In the present study, Hortaea werneckii R23, produced a black pigment in the yeast biomass. The pigment was extracted from the harvested yeast biomass and followed by pigment purification, characterization and identification was done. Physicochemical characterization of the pigment showed acid precipitation, alkali solubilization, insolubility in most organic solvents and water. The black pigment was confirmed as melanin based on ultraviolet-visible spectroscopy, Fourier-transform infrared, and Nuclear magnetic resonance spectroscopy analyses. Furthermore, the analyses of the elemental composition indicated that the pigment possessed a moderately high percentage of nitrogen and also detectable proportion of sulfur. All these Physicochemical properties indicated that H. werneckii melanin (HwM) mostly consisted of eumelanin. HwM exhibited strong antioxidant potential as reactive oxygen species (ROS) scavenger by in vitro DPPH (1,1-diphenyl-2-picryl hydrazyl) and ABTS (2,2-azinobis-3-ethyl-benzothiozoline-6-sulphonic acid) radical scavenging assay, and lipid peroxidation assay. The photoprotectant role of HwM on UV-irradiated human epithelial cells (HEp-2) revealed its potential effect in photoprotection. In addition, cytotoxicity study by XTT and SRB assay confirmed its biocompatibility with HEp-2 cells. From these findings, it is evident that the HwM from the marine black yeast possesses strong antioxidant and photoprotectant activity, moreover, it is biocompatible to human epithelial cells. So HwM could be used as a protective agent against oxidative stress associated disorders in an environment-friendly perspective.

Bioproduction and optimization of newly characterized melanin pigment from Streptomyces djakartensis NSS-3 with its anticancer, antimicrobial, and radioprotective properties

BACKGROUND

Melanin is a natural pigment that is considered a promising biomaterial for numerous biotechnological applications across several industries. Melanin has biomedical applications as antimicrobial, anticancer, and antioxidant properties. Additionally, in the pharmaceutical and cosmetic industries, it is used in drug delivery and as a radioprotective agent. Also, melanin has environmental uses in the fields of bioremediation and the food industry. The biosynthesis of melanin pigment is an area of interest for researchers due to its multifunctionality, high compatibility, and biodegradability. Therefore, our present work is the first attempt to characterize and optimize the productivity of melanin pigment from Streptomyces djakartensis NSS-3 concerning its radioprotection and biological properties.

RESULTS

Forty isolates of soil actinobacteria were isolated from the Wadi Allaqui Biosphere Reserve, Egypt. Only one isolate, ACT3, produced a dark brown melanin pigment extracellularly. This isolate was identified according to phenotypic properties and molecular phylogenetic analysis as Streptomyces djakartensis NSS-3 with accession number OP912881. Plackett-Burman experimental design (PBD) and response surface methodology (RSM) using a Box-Behnken design (BBD) were performed for optimum medium and culturing conditions for maximum pigment production, resulting in a 4.19-fold improvement in melanin production (118.73 mg/10 mL). The extracted melanin pigment was purified and characterized as belonging to nitrogen-free pyomelanin based on ultraviolet-visible spectrophotometry (UV-VIS), Fourier transform infrared (FT-IR), Raman spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and NMR studies. Purified melanin demonstrated potent scavenging activity with IC50 values of 18.03 µg/mL and revealed high potency as sunscreens (in vitro SPF = 18.5). Moreover, it showed a nontoxic effect on a normal cell line (WI38), while it had a concentration-dependent anticancer effect on HCT116, HEPG, and MCF7 cell lines with IC50 = 108.9, 43.83, and 81.99 µg/mL, respectively. Also, purified melanin had a detrimental effect on the tested MDR bacterial strains, of which PA-09 and SA-04 were clearly more susceptible to melanin compared with other strains with MICs of 6.25 and 25 µg/mL, respectively.

CONCLUSION

Our results demonstrated that the newly characterized pyomelanin from Streptomyces djakartensis NSS-3 has valuable biological properties due to its potential photoprotective, antioxidant, anticancer, antimicrobial, and lack of cytotoxic activities, which open up new prospects for using this natural melanin pigment in various biotechnological applications and avoiding chemical-based drugs.

Bacteria as biofactory of pigments: Evolution beyond therapeutics and biotechnological advancements

Bacterial pigments are the wonder molecules of nature that have attracted the attention of industries in recent years. To date, various synthetic pigments have been in use in food, cosmetics, and textile industries that have not only shown a notoriously toxic nature but also posed threat to the ecosystem. Moreover, nutraceuticals, fisheries, and animal husbandry were highly dependent on plant sources for products that aid in disease prevention and improve stock health. In this context, the use of bacterial pigments as new-generation colorants, food fortifiers, and supplements can hold great prospects as low-cost, healthy, and eco-friendly alternatives. The majority of studies on these compounds were restricted to antimicrobial, antioxidant, and anticancer potentials to date. Each of these can be highly beneficial for the development of new-generation drugs, but their other potential niche in various industries that pose health and environmental risks needs to be explored. Recent advances in novel strategies of metabolic engineering, advancements in optimization tools for the fermentation process, and the design of appropriate delivery systems will greatly expand the market of bacterial pigments in industries. This review summarizes the current technologies for enhancing production, recovery, stability, and appreciable use of bacterial pigments in industries apart from therapeutics with proper financial aspects. The toxicity perspectives have been focused to emphasize that these wonder molecules are the need of the hour and their future prospects have been highlighted. Extensive literature has been studied to include the challenges of bacterial pigments from environmental and health risk perspectives.

Evaluation of the composition of konjac glucomannan on the color changes during the deacetylation reaction

As a newly superior konjac variety, the Amorphophallus bulbifer (A. bulbifer) has several unique advantages of high reproductive coefficient, short growth cycle, high disease resistance, high konjac glucomannan (KGM) content and climate adaption to hot or humid conditions. However, the gel formed by KGM from the A. bulbifer flour is easily browning during the alkali-induced process and the mechanism underlying them is still unclear. In order to explore the browning mechanisms, the changes of composition and color parameters of KGM were investigated during deacetylation in this research. The L*, h*, total phenols, total flavonoids, reducing sugars, and amino acids decreased along with the increase of deacetylation degree of KGM while a*, ΔЕ, and browning index increased. The results indicated that the oxidation or polymerization of polyphenols and flavones in alkaline circumstances, and the carbonyl ammonia reaction between reducing sugars and amino acids may be the main reasons for color changes of KGM flour during deacetylation. Hence, this study was expected to provide the theoretical basis for the inhibition of KGM gel browning and further broaden the application range of KGM in food and other industries.

Effects of W/O Nanoemulsion on Improving the Color Tone of Beijing Roast Duck

Traditional Beijing roast duck is often brushed with a high concentration of maltose solution (15% w/v) and shows ununiform color after roasting. A novel W/O nanoemulsion was applied to improve the color tone of Beijing roast ducks and, meanwhile, reduced the amount of sugar. For the W/O emulsion, 3% (w/v) xylose solution as the aqueous phase, soybean oil as the oil phase, and polyglycerol polyricinoleate (PGPR) and whey protein isolate (WPI) as co-emulsifiers were fabricated by high-pressure homogenization. Particle size measurement by Zetasizer and stability analysis by Turbiscan stability analyzer showed that WPI as co-emulsifier and internal aqueous phase at pH 9 decreased the droplet size and improved the emulsion stability. In addition, by color difference evaluation, the W/O nanoemulsion improved the Maillard reaction degree and color tone of Beijing roast duck. The molecular structure and key composition of pigments on the surface of Beijing roast duck skins were also identified and characterized by UV-vis spectroscopy and UHPLC-MS. This study creatively offers theoretical guidance for increasing applications of W/O-nanoemulsion-based Maillard reaction in the roast food industry, especially for the development of reduced-sugar Beijing roast duck with uniform and desired color satisfying consumers' acceptance and marketability.

Biocolorants in food: Sources, extraction, applications and future prospects

Color of a food is one of the major factors influencing its acceptance by consumers. At presently synthetic dyes are the most commonly used food colorant in food industry by providing more esthetically appearance and as a means to quality control. However, the growing concern about health and environmental due to associated toxicity with synthetic food colorants has accelerated the global efforts to replace them with safer and healthy food colorants obtained from natural resources (plants, microorganisms, and animals). Further, many of these biocolorants not only provide myriad of colors to the food but also exert biological properties, thus they can be used as nutraceuticals in foods and beverages. In order to understand the importance of nature-derived pigments as food colorants, this review provides a thorough discussion on the natural origin of food colorants. Following this, different extraction methods for isolating biocolorants from plants and microbes were also discussed. Many of these biocolorants not only provide color, but also have many health promoting properties, for this reason their physicochemical and biological properties were also reviewed. Finally, current trends on the use of biocolorants in foods, and the challenges faced by the biocolorants in their effective utilization by food industry and possible solutions to these challenges were discussed.

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.

MaAts, an Alkylsulfatase, Contributes to Fungal Tolerances against UV-B Irradiation and Heat-Shock in Metarhizium acridum

Sulfatases are commonly divided into three classes: type I, type II, and type III sulfatases. The type III sulfatase, alkylsulfatase, could hydrolyze the primary alkyl sulfates, such as sodium dodecyl sulfate (SDS) and sodium octyl sulfate. Thus, it has the potential application of SDS biodegradation. However, the roles of alkylsulfatase in biological control fungus remain unclear. In this study, an alkylsulfatase gene MaAts was identified from Metarhizium acridum. The deletion strain (ΔMaAts) and the complemented strain (CP) were constructed to reveal their functions in M. acridum. The activity of alkylsulfatase in ΔMaAts was dramatically reduced compared to the wild-type (WT) strain. The loss of MaAts delayed conidial germination, conidiation, and significantly declined the fungal tolerances to UV-B irradiation and heat-shock, while the fungal conidial yield and virulence were unaffected in M. acridum. The transcription levels of stress resistance-related genes were significantly changed after MaAts inactivation. Furthermore, digital gene expression profiling showed that 512 differential expression genes (DEGs), including 177 up-regulated genes and 335 down-regulated genes in ΔMaAts, were identified. Of these DEGs, some genes were involved in melanin synthesis, cell wall integrity, and tolerances to various stresses. These results indicate that MaAts and the DEGs involved in fungal stress tolerances may be candidate genes to be adopted to improve the stress tolerances of mycopesticides.

Characterization of an Insoluble and Soluble Form of Melanin Produced by Streptomyces cavourensis SV 21, a Sea Cucumber Associated Bacterium

Melanin is a widely distributed and striking dark-colored pigment produced by countless living organisms. Although a wide range of bioactivities have been recognized, there are still major constraints in using melanin for biotechnological applications such as its fragmentary known chemical structure and its insolubility in inorganic and organic solvents. In this study, a bacterial culture of Streptomyces cavourensis SV 21 produced two distinct forms of melanin: (1) a particulate, insoluble form as well as (2) a rarely observed water-soluble form. The here presented novel, acid-free purification protocol of purified particulate melanin (PPM) and purified dissolved melanin (PDM) represents the basis for an in-depth comparison of their physicochemical and biological properties, which were compared to the traditional acid-based precipitation of melanin (AM) and to a synthetic melanin standard (SM). Our data show that the differences in solubility between PDM and PPM in aqueous solutions may be a result of different adjoining cation species, since the soluble PDM polymer is largely composed of Mg²⁺ ions and the insoluble PPM is dominated by Ca²⁺ ions. Furthermore, AM shared most properties with SM, which is likely attributed to a similar, acid-based production protocol. The here presented gentler approach of purifying melanin facilitates a new perspective of an intact form of soluble and insoluble melanin that is less chemical altered and thus closer to its original biological form.

Natural Pigments of Bacterial Origin and Their Possible Biomedical Applications

Microorganisms are considered one of the most promising niches for prospecting, production, and application of bioactive compounds of biotechnological interest. Among them, bacteria offer certain distinctive advantages due to their short life cycle, their low sensitivity to seasonal and climatic changes, their easy scaling as well as their ability to produce pigments of various colors and shades. Natural pigments have attracted the attention of industry due to an increasing interest in the generation of new products harmless to humans and nature. This is because pigments of artificial origin used in industry can have various deleterious effects. On this basis, bacterial pigments promise to be an attractive niche of new biotechnological applications, from functional food production to the generation of new drugs and biomedical therapies. This review endeavors to establish the beneficial properties of several relevant pigments of bacterial origin and their relation to applications in the biomedical area.

Production, purification, and process optimization of intracellular pigment from novel psychrotolerant Paenibacillus sp. BPW19

A pink pigment-producing bacterial strain was isolated from wastewater and identified as Paenibacillus sp. BPW19. The motile bacterial strain was Gram-positive, acid fermenting, glucose, sucrose utilizing and rod-shaped with an average cell length of 1.55 μm as studied under the Environmental Scanning Electron Microscope. Even though being psychrotolerant, the cell growth condition of BPW19 was optimized as 25 ºC along with pH 8, and 2.25% inoculum concentration considering the operational ease of the production. Sonication assisted solvent extraction produced 5.41% crude pigment which showed zones of exclusion against gram-negative strains Escherichia coli DH5α, Enterobacter sp. EtK3, and Klebsiella sp. SHC1. Gas Chromatography-Mass Spectrometry analysis of the crude pigment exhibited the dominant presence of major compounds as dotriacontane; 3,7 dimethyl 7 octanal; 1-eicosene and erucic acid. While column chromatography (ethanol:chloroform in 1:4 (v/v) ratio) purified pigment was identified as erucic acid using Nuclear Magnetic Resonance with a net yield of 3.06%.

Pigments from Antarctic bacteria and their biotechnological applications

Pigments from microorganisms have triggered great interest in the market, mostly by their "natural" appeal, their favorable production conditions, in addition to the potential new chemical structures or naturally overproducing strains. They have been used in: food, feed, dairy, textile, pharmaceutical, and cosmetic industries. The high rate of pigment production in microorganisms recovered from Antarctica in response to selective pressures such as: high UV radiation, low temperatures, and freezing and thawing cycles makes this a unique biome which means that much of its biological heritage cannot be found elsewhere on the planet. This vast arsenal of pigmented molecules has different functions in bacteria and may exhibit different biotechnological activities, such as: extracellular sunscreens, photoprotective function, antimicrobial activity, biodegradability, etc. However, many challenges for the commercial use of these compounds have yet to be overcome, such as: the low stability of natural pigments in cosmetic formulations, the change in color when subjected to pH variations, the low yield and the high costs in their production. This review surveys the different types of natural pigments found in Antarctic bacteria, classifying them according to their chemical structure. Finally, we give an overview of the main pigments that are used commercially today.

Microbiota entrapped in recently-formed ice: Paradana Ice Cave, Slovenia

Paradana is one of the biggest ice caves in Slovenia, with an estimated ice volume of 8,000 m³. Reflecting climatological conditions, the cave ice undergoes repeated freeze-thaw cycles and regular yearly deposition of fresh ice. Three distinct ice block samples, collected from the frozen lake in May 2016, were analysed to obtain data on ice physicochemical properties and the composition of associated microbiota. Isotopic composition of the ice samples (¹⁸O, ²H) and a local meteoric water line (LMWL) constructed for monthly precipitation at Postojna were used to estimate the isotopic composition of the water that formed the ice, which had high values of deuterium excess and low concentrations of chloride, sulphate and nitrate. The values of total organic carbon (1.93–3.95 mg/l) within the ice blocks fall within the range of those measured in karst streams. Total cell count in the ice was high and the proportion of cell viability increased along the depth gradient and ranged from 4.67 × 10⁴ to 1.52 × 10⁵ cells/ml and from 51.0 to 85.4%, respectively. Proteobacteria represented the core of the cave-ice microbiome (55.9–79.1%), and probably play an essential role in this ecosystem. Actinobacteria was the second most abundant phylum (12.0–31.4%), followed in abundance by Bacteroidetes (2.8–4.3%). Ice phylotypes recorded amounted to 442 genera, but only 43 genera had abundances greater than 0.5%. Most abundant were Pseudomonas, a well-known ice dweller, and Lysobacter, which previously was not reported in this context. Finally, two xanthophytes, Chloridella glacialis and Ellipsoidion perminimum, known from polar environments, were cultured from the ice. This indicates that the abundance and ecological role of phototrophs in such environments might be greater than previously deduced.

Identifying and characterizing the components related to the brown color of Chinese sugar-smoked chicken during processing

The desired color is a key indicator for consumer acceptability of Chinese sugar-smoked chicken. To investigate the formation of color attributes of Chinese sugar-smoked chicken during processing, color values, structural characteristics, and components of brown pigment were evaluated in 2 groups, which were defined as brown skin (BS) and normal skin (NS) of Chinese sugar-smoked chicken based on their color values. Compared with the NS samples, the BS samples showed significantly lower values of lightness, redness, and yellowness and higher content of malondialdehyde and 5-hydroxymethylfurfural. UV-visible and Fourier-transform infrared spectra suggested that the structure of brown pigment was similar to melanin. The brown pigment consisted of multiple chemical components including the polymer of fructose and glucose, and derivatives produced by lipid oxidation, which were identified by HPLC-tandem mass spectrometry. The polymer content of glucose and fructose, which was demonstrated as sucrose by HPLC analysis, was higher in the BS group than in the NS group. Our results indicated that the higher content of the polymer of glucose and fructose was mainly responsible for the brown color of Chinese sugar-smoked chicken.

Pigment production by cold-adapted bacteria and fungi: colorful tale of cryosphere with wide range applications

Pigments are an essential part of everyday life on Earth with rapidly growing industrial and biomedical applications. Synthetic pigments account for a major portion of these pigments that in turn have deleterious effects on public health and environment. Such drawbacks of synthetic pigments have shifted the trend to use natural pigments that are considered as the best alternative to synthetic pigments due to their significant properties. Natural pigments from microorganisms are of great interest due to their broader applications in the pharmaceutical, food, and textile industry with increasing demand among the consumers opting for natural pigments. To fulfill the market demand of natural pigments new sources should be explored. Cold-adapted bacteria and fungi in the cryosphere produce a variety of pigments as a protective strategy against ecological stresses such as low temperature, oxidative stresses, and ultraviolet radiation making them a potential source for natural pigment production. This review highlights the protective strategies and pigment production by cold-adapted bacteria and fungi, their industrial and biomedical applications, condition optimization for maximum pigment extraction as well as the challenges facing in the exploitation of cryospheric microorganisms for pigment extraction that hopefully will provide valuable information, direction, and progress in forthcoming studies.

Copper and Melanin Play a Role in Myxococcus xanthus Predation on Sinorhizobium meliloti

Myxococcus xanthus is a soil myxobacterium that exhibits a complex lifecycle with two multicellular stages: cooperative predation and development. During predation, myxobacterial cells produce a wide variety of secondary metabolites and hydrolytic enzymes to kill and consume the prey. It is known that eukaryotic predators, such as ameba and macrophages, introduce copper and other metals into the phagosomes to kill their prey by oxidative stress. However, the role of metals in bacterial predation has not yet been established. In this work, we have addressed the role of copper during predation of M. xanthus on Sinorhizobium meliloti. The use of biosensors, variable pressure scanning electron microscopy, high-resolution scanning transmission electron microscopy, and energy dispersive X ray analysis has revealed that copper accumulates in the region where predator and prey collide. This accumulation of metal up-regulates the expression of several mechanisms involved in copper detoxification in the predator (the P_1B-ATPase CopA, the multicopper oxidase CuoA and the tripartite pump Cus2), and the production by the prey of copper-inducible melanin, which is a polymer with the ability to protect cells from oxidative stress. We have identified two genes in S. meliloti (encoding a tyrosinase and a multicopper oxidase) that participate in the biosynthesis of melanin. Analysis of prey survivability in the co-culture of M. xanthus and a mutant of S. meliloti in which the two genes involved in melanin biosynthesis have been deleted has revealed that this mutant is more sensitive to predation than the wild-type strain. These results indicate that copper plays a role in bacterial predation and that melanin is used by the prey to defend itself from the predator. Taking into consideration that S. meliloti is a nitrogen-fixing bacterium in symbiosis with legumes that coexists in soils with M. xanthus and that copper is a common metal found in this habitat as a consequence of several human activities, these results provide clear evidence that the accumulation of this metal in the soil may influence the microbial ecosystems by affecting bacterial predatory activities.

Melanin biosynthesis in bacteria, regulation and production perspectives

The production of black pigments in bacteria was discovered more than a century ago and related to tyrosine metabolism. However, their diverse biological roles and the control of melanin synthesis in different bacteria have only recently been investigated. The broad distribution of these pigments suggests that they have an important role in a variety of organisms. Melanins protect microorganisms from many environmental stress conditions, ranging from ultraviolet radiation and toxic heavy metals to oxidative stress. Melanins can also affect bacterial interactions with other organisms and are important in pathogenesis and survival in many environments. Bacteria produce several types of melanin through dedicated pathways or as a result of enzymatic imbalances in altered metabolic routes. The control of the melanin synthesis in bacteria involves metabolic and transcriptional regulation, but many aspects remain still largely unknown. The diverse properties of melanins have spurred a large number of applications, and recent efforts have been done to produce the pigment at biotechnologically relevant scales.

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.

Soluble melanins of the Randia echinocarpa fruit - Structural characteristics and toxicity

The water-soluble melanins (SM) of Randia echinocarpa fruit possess interesting biological activities and have been scarcely characterized. In this study, SM were obtained at boiling (SMBT) and room (SMRT) temperatures and characterized by UV-Vis, IR, thermogravimetric analysis, and GC-MS of the hydrolysis products of the SM; besides, the solid-state ¹³ C NMR, elemental analysis, and acute and sub-acute toxicity of the SMBT were determined. SMBT and SMRT contain organic acids and carbohydrates and their spectroscopic signals and thermograms were similar, but the SMBT yield was higher. The SMBT were characterized by their elemental composition (C 48.260 ± 0.011%, N 3.693 ± 0.009% and H 6.093 ± 0.076%) consistent with the presence of aromatic rings and eumelanins, degradation temperature at 300°C, ¹³ C NMR signals supporting melanin-bonding with carbohydrates and organic acids, and innocuity in Balb/C mice (acute assay, LD₅₀  > 5 g/kg b.w.; sub-acute assay, no lethality at 500 mg/kg b.w. for 30 days). PRACTICAL APPLICATIONS: The consumption of melanins has been associated with health benefits because of their biological activities (e.g., antioxidant, immunostimulatory, UV- and radiation-protective). Randia echinocarpa is employed in Mexican traditional medicine against chronic degenerative diseases (e.g., cancer and diabetes) and ailments of organs (e.g., kidney and lung) and systems (e.g., circulatory and gastrointestinal). The R. echinocarpa fruit contains water-soluble melanins (SM) that inhibit carbohydrate-digestive enzymes and show high antioxidant activity; thus, SM could be useful for the prevention and treatment of diabetes. This study showed that the SM structure contains melanin-bonding organic acids and carbohydrates, which could be associated with the SM solubility and higher yield, and that SMBT were innocuous in the acute and sub-acute assays in mice. Thus, the R. echinocarpa SMBT could be used as safe potential ingredients to develop functional products.

UV-Protective Compounds in Marine Organisms from the Southern Ocean

Solar radiation represents a key abiotic factor in the evolution of life in the oceans. In general, marine, biota-particularly in euphotic and dysphotic zones-depends directly or indirectly on light, but ultraviolet radiation (UV-R) can damage vital molecular machineries. UV-R induces the formation of reactive oxygen species (ROS) and impairs intracellular structures and enzymatic reactions. It can also affect organismal physiologies and eventually alter trophic chains at the ecosystem level. In Antarctica, physical drivers, such as sunlight, sea-ice, seasonality and low temperature are particularly influencing as compared to other regions. The springtime ozone depletion over the Southern Ocean makes organisms be more vulnerable to UV-R. Nonetheless, Antarctic species seem to possess analogous UV photoprotection and repair mechanisms as those found in organisms from other latitudes. The lack of data on species-specific responses towards increased UV-B still limits the understanding about the ecological impact and the tolerance levels related to ozone depletion in this region. The photobiology of Antarctic biota is largely unknown, in spite of representing a highly promising reservoir in the discovery of novel cosmeceutical products. This review compiles the most relevant information on photoprotection and UV-repair processes described in organisms from the Southern Ocean, in the context of this unique marine polar environment.

Study of melanin localization in the mature male Calopteryx haemorrhoidalis damselfly wings

Damselflies Calopteryx haemorrhoidalis exhibiting black wings are found in the western Mediterranean, Algeria, France, Italy, Spain and Monaco. Wing pigmentation is caused by the presence of melanin, which is involved in physiological processes including defence reactions, wound healing and sclerotization of the insect. Despite the important physiological roles of melanin, the presence and colour variation among males and females of the C. haemorrhoidalis species and the localization of the pigment within the wing membrane remain poorly understood. In this study, infrared (IR) microspectroscopy, coupled with the highly collimated synchrotron IR beam, was employed in order to identify the distribution of the pigments in the wings at a high spatial resolution. It was found that the melanin is localized in the procuticle of the C. haemorrhoidalis damselfly wings, distributed homogeneously within this layer, and not associated with the lipids of the epicuticle.

Genome sequence of Lysobacter dokdonensis DS-58(T), a gliding bacterium isolated from soil in Dokdo, Korea

Lysobacter dokdonensis DS-58, belonging to the family Xanthomonadaceae, was isolated from a soil sample in Dokdo, Korea in 2011. Strain DS-58 is the type strain of L. dokdonensis. In this study, we determined the genome sequence to describe the genomic features including annotation information and COG functional categorization. The draft genome sequence consists of 25 contigs totaling 3,274,406 bp (67.24 % G + C) and contains 3,155 protein coding genes, 2 copies of ribosomal RNA operons, and 48 transfer RNA genes. Among the protein coding genes, 75.91 % of the genes were annotated with a putative function and 87.39 % of the genes were assigned to the COG category. In the genome of L. dokdonensis, a large number of genes associated with protein degradation and antibiotic resistance were detected.

Production of natural edible melanin by Auricularia auricula and its physicochemical properties

Fermentation conditions of natural edible melanin by Auricularia auricula were optimized to obtain a high melanin yield and physicochemical properties of melanin were firstly investigated. The results indicated that yeast extract, tyrosine and lactose have significant effects on melanin production. Under the proposed optimized conditions, the melanin experimental yield (2.97 g/L) closely matched the value (3.04 g/L) predicted by the second-order model, which provided a statistically prediction of media in submerged fermentation of A. auricula. The yield achieved was 2.14-fold higher compared to the control. It was firstly revealed that tyrosine could stimulate melanin synthesis in A. auricula. The results showed that this melanin had better thermostability and light resistance, and its solubility was relatively high under alkaline conditions. Zn(2+) and Cu(2+) could result in melanin precipitation. The results should be useful for the efficient production of melanin and enable numerous applications in food, cosmetics, pharmacology, medicines and other fields.