Melanin biosynthesis in bacteria, regulation and production perspectives

The structural complexity of pyomelanin impacts UV shielding in Pseudomonas species with different lifestyles

Pyomelanin, a polymeric pigment in Pseudomonas, arises mainly from alterations in tyrosine degradation. The chemical structure of pyomelanin remains elusive due to its heterogeneous nature. Here, we report strain-specific differences in pyomelanin structural features across Pseudomonas using PAO1 and PA14 reference strains carrying mutations in hmgA (a gene involved in pyomelanin synthesis), a melanogenic P. aeruginosa clinical isolate (PAM), and a melanogenic P. extremaustralis (PexM). UV spectra showed dual peaks for PAO1 and PA14 mutants and single peaks for PAM and PexM. FTIR phenol : alcohol ratio changes and complex NMR spectra indicated non-linear polymers. UVC radiation survival increased with pyomelanin addition, correlating with pigment absorption attenuation. P. extremaustralis UVC survival varied with melanin source, with PAO1 pyomelanin being the most protective. These findings delineate structure-based pyomelanin subgroups, having distinct physiological effects.

Physiological Roles of Eumelanin- and Melanogenesis-Associated Diseases: A Look at the Potentialities of Engineered and Microbial Eumelanin in Clinical Practice

This paper aims to highlight the physiological actions exerted by eumelanin present in several organs/tissues of the human body and to rationalise the often conflicting functional roles played by this biopolymer on the basis of its peculiar properties. Besides pigmentary disorders, a growing number of organ injuries and degenerative pathologies are presently ascribed to the modification of physiological eumelanin levels in terms of alterations in its chemical/structural features, and of a partial loss or uneven distribution of the pigment. The present review analyses the more recent research dedicated to the physiological and pathological actions of eumelanin and provides an insight into some melanogenesis-associated diseases of the skin, eye, ear, and brain, including the most significant neurodegenerative disorders. Also described are the potentialities of therapies based on the localised supply of exogeneous EU and the opportunities that EU produced via synthetic biology offers in order to redesign therapeutical and diagnostic applications.

Draft genome of the marine bacterium Alteromonas gracilis strain J4 isolated from the green coenocytic alga Caulerpa prolifera

Here, we present the draft genome sequence of Alteromonas gracilis strain J4, isolated from the green macroalga Caulerpa prolifera. The draft genome is 4,492,914 bp in size and contains 4,719 coding DNA sequences, 67 tRNAs, and 16 rRNA-coding genes. Strain J4 may exhibit host growth-promoting properties.

Mutation of hmgA, encoding homogentisate 1,2-dioxygenase, is responsible for pyomelanin production but does not impact the virulence of Burkholderia cenocepacia in a chronic granulomatous disease mouse lung infection

The Burkholderia cepacia complex (Bcc) is a group of Gram-negative opportunistic bacteria often associated with fatal pulmonary infections in patients with impaired immunity, particularly those with cystic fibrosis (CF) and chronic granulomatous disease (CGD). Some Bcc strains are known to naturally produce pyomelanin, a brown melanin-like pigment known for scavenging free radicals; pigment production has been reported to enable Bcc strains to overcome the host cell oxidative burst. In this work, we investigated the role of pyomelanin in resistance to oxidative stress and virulence in strains J2315 and K56-2, two epidemic CF isolates belonging to the Burkholderia cenocepacia ET-12 lineage. We previously reported that a single amino acid change from glycine to arginine at residue 378 in homogentisate 1,2-dioxygenase (HmgA) affects the pigment production phenotype: pigmented J2315 has an arginine at position 378, while non-pigmented K56-2 has a glycine at this position. Herein, we performed allelic exchange to generate isogenic non-pigmented and pigmented strains of J2315 and K56-2, respectively, and tested these to determine whether pyomelanin contributes to the protection against oxidative stress in vitro as well as in a respiratory infection in CGD mice in vivo. Our results indicate that the altered pigment phenotype does not significantly impact these strains' ability to resist oxidative stress with H2O2 and NO in vitro and did not change the virulence and infection outcome in CGD mice in vivo suggesting that other factors besides pyomelanin are contributing to the pathophysiology of these strains.IMPORTANCEThe Burkholderia cepacia complex (Bcc) is a group of Gram-negative opportunistic bacteria that are often associated with fatal pulmonary infections in patients with impaired immunity, particularly those with cystic fibrosis and chronic granulomatous disease (CGD). Some Bcc strains are known to naturally produce pyomelanin, a brown melanin-like pigment known for scavenging free radicals and overcoming the host cell oxidative burst. We investigated the role of pyomelanin in Burkholderia cenocepacia strains J2315 (pigmented) and K56-2 (non-pigmented) and performed allelic exchange to generate isogenic non-pigmented and pigmented strains, respectively. Our results indicate that the altered pigment phenotype does not significantly impact these strains' ability to resist H2O2 or NO in vitro and did not alter the outcome of a respiratory infection in CGD mice in vivo. These results suggest that pyomelanin may not always constitute a virulence factor and suggest that other features are contributing to the pathophysiology of these strains.

Physicochemical characterization of the brown pigment produced by Azospirillum brasilense HM053 using tryptophan as precursor

Microorganisms are known to be a promising source of biopigments because they are easy to obtain, can be produced on a commercial scale, and are environmentally friendly. Therefore, the aim of this work was to characterize a brown pigment (BP) produced by HM053 in NFbHPN-lactate medium. The BP was extracted from the pellet (BPP) or supernatant (BPS), in the presence (BPPTrp, BPSTrp) or absence (BPPw, BPSw) of tryptophan (Trp). The UV-vis results were similar among all BP samples and compared with commercial melanin used as a standard, and the maximum absorption was observed around 200-220 nm. FTIR spectra showed that BP and commercial melanin had slight differences, with a small band between 3000-2840 cm- 1, related to C-H in the CH2 and CH3 aliphatic groups, which is not observed in the commercial melanin. Between BPP and BPS showed a different structure with bands in the region 1230-1070 cm- 1 related to groups C-O. The thermogravimetric curves for BPSw and BPSTrp showed similar behavior, with 4 stages of mass loss. The similarity between BPPw and BPPTrp with 2 stages of mass loss was also observed. Scanning electron microscopy results showed morphological differences between BPP and BPS, where BPP had a physical structure more homogeneous and a regular flat surface, while the BPS physical structure did not seem homogeneous and the surface was uneven with some spherical structures as commercial melanin.

Exploring the Agricultural Applications of Microbial Melanin

Microbial melanins are a group of pigments with protective effects against harsh conditions, showing fascinating photoprotective activities, mainly due to their capability to absorb UV radiation. In bacteria, they are produced by the oxidation of L-tyrosine, generating eumelanin and pheomelanin. Meanwhile, allomelanin is produced by fungi through the decarboxylative condensation of malonyl-CoA. Moreover, melanins possess antioxidant and antimicrobial activities, revealing significant properties that can be used in different industries, such as cosmetic, pharmaceutical, and agronomical. In agriculture, melanins have potential applications, including the development of new biological products based on this pigment for the biocontrol of phytopathogenic fungi and bacteria to reduce the excessive and toxic levels of agrochemicals used in fields. Furthermore, there are possibilities to develop and improve new bio-based pesticides that control pest insects through the use of melanin-producing and toxin-producing Bacillus thuringiensis or through the application of melanin to insecticidal proteins to generate a new product with improved resistance to UV radiation that can then be applied to the plants. Melanins and melanin-producing bacteria have potential applications in agriculture due to their ability to improve plant growth. Finally, the bioremediation of water and soils is possible through the application of melanins to polluted soils and water, removing synthetic dyes and toxic metals.

Increased secretion of bacterial pyomelanin caused by light accelerates corrosion of low alloy steel

Microorganisms in the waterline zone can secrete pigments to avoid damage caused by ultraviolet radiation, some of which have corrosive effects. In this work, we found that the secretion of pyomelanin by P3 strain of Pseudoalteromonas lipolytica significantly increases under strong lighting conditions, accelerating the corrosion of the material. Molecular mechanisms indicate that strong light, as a stressful environmental factor, enhances the expression of melanin secretion-related genes to prevent bacteria from being damaged by ultraviolet radiation. Therefore, this work proposes a new corrosion mechanism in the waterline zone, pigment-producing microorganisms are also involved in the waterline corrosion process.

Skin microbiome profiling reveals the crucial role of microbial metabolites in anti-photoaging

BACKGROUND

Skin microbiota is essential for health maintenance. Photoaging is the primary environmental factor that affects skin homeostasis, but whether it influences the skin microbiota remains unclear.

OBJECTIVE

The objective of this study is to investigate the relationship between photoaging and skin microbiome.

METHODS

A cohort of senior bus drivers was considered as a long-term unilateral ultraviolet (UV) irradiated population. 16S rRNA amplicon sequencing was conducted to assess skin microbial composition variations on different sides of their faces. The microbiome characteristics of the photoaged population were further examined by photoaging guinea pig models, and the correlations between microbial metabolites and aging-related cytokines were analyzed by high-throughput sequencing and reverse transcription polymerase chain reaction.

RESULTS

Photoaging decreased the relative abundance of microorganisms including Georgenia and Thermobifida in human skin and downregulated the generation of skin microbe-derived antioxidative metabolites such as ectoin. In animal models, Lactobacillus and Streptobacillus abundance in both the epidermis and dermis dropped after UV irradiation, resulting in low levels of skin antioxidative molecules and leading to elevated expressions of the collagen degradation factors matrix metalloproteinase (MMP)-1 and MMP-2 and inflammatory factors such as interleukin (IL)-1β and IL-6.

CONCLUSIONS

Skin microbial characteristics have an impact in photoaging and the loss of microbe-derived antioxidative metabolites impairs skin cells and accelerates the aging process. Therefore, microbiome-based therapeutics may have potential in delaying skin aging.

Interactions of Melanin with Electromagnetic Radiation: From Fundamentals to Applications

Melanin, especially integumentary melanin, interacts in numerous ways with electromagnetic radiation, leading to a set of critical functions, including radiation protection, UV-protection, pigmentary and structural color productions, and thermoregulation. By harnessing these functions, melanin and melanin-like materials can be widely applied to diverse applications with extraordinary performance. Here we provide a unified overview of the melanin family (all melanin and melanin-like materials) and their interactions with the complete electromagnetic radiation spectrum (X-ray, Gamma-ray, UV, visible, near-infrared), which until now has been absent from the literature and is needed to establish a solid fundamental base to facilitate their future investigation and development. We begin by discussing the chemistries and morphologies of both natural and artificial melanin, then the fundamentals of melanin-radiation interactions, and finally the exciting new developments in high-performance melanin-based functional materials that exploit these interactions. This Review provides both a comprehensive overview and a discussion of future perspectives for each subfield of melanin that will help direct the future development of melanin from both fundamental and applied perspectives.

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

Introducion

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

Materials and methods

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

Results

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

Discussion

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

AHL-Based Quorum Sensing Regulates the Biosynthesis of a Variety of Bioactive Molecules in Bacteria

Bacteria are social microorganisms that use communication systems known as quorum sensing (QS) to regulate diverse cellular behaviors including the production of various secreted molecules. Bacterial secondary metabolites are widely studied for their bioactivities including antibiotic, antifungal, antiparasitic, and cytotoxic compounds. Besides playing a crucial role in natural bacterial niches and intermicrobial competition by targeting neighboring organisms and conferring survival advantages to the producer, these bioactive molecules may be of prime interest to develop new antimicrobials or anticancer therapies. This review focuses on bioactive compounds produced under acyl homoserine lactone-based QS regulation by Gram-negative bacteria that are pathogenic to humans and animals, including the Burkholderia, Serratia, Pseudomonas, Chromobacterium, and Pseudoalteromonas genera. The synthesis, regulation, chemical nature, biocidal effects, and potential applications of these identified toxic molecules are presented and discussed in light of their role in microbial interactions.

Blue Biotechnology: Marine Bacteria Bioproducts

The ocean is the habitat of a great number of organisms with different characteristics. Compared to terrestrial microorganisms, marine microorganisms also represent a vast and largely unexplored reservoir of bioactive compounds with diverse industrial applications like terrestrial microorganisms. This review examines the properties and potential applications of products derived from marine microorganisms, including bacteriocins, enzymes, exopolysaccharides, and pigments, juxtaposing them in some cases against their terrestrial counterparts. We discuss the distinct characteristics that set marine-derived products apart, including enhanced stability and unique structural features such as the amount of uronic acid and sulfate groups in exopolysaccharides. Further, we explore the uses of these marine-derived compounds across various industries, ranging from food and pharmaceuticals to cosmetics and biotechnology. This review also presents a broad description of biotechnologically important compounds produced by bacteria isolated from marine environments, some of them with different qualities compared to their terrestrial counterparts.

Production and characterization of melanin pigment from black fungus Curvularia soli AS21 ON076460 assisted gamma rays for promising medical uses

Owing to the growing need for natural materials in different fields, studying melanin production from biological sources is imperative. In the current study, the extracellular melanin pigment was produced by the fungus Curvularia soli AS21 ON076460. The factors that affect the production of melanin were optimized by the Plackett-Burman design (P-BD). The effect of gamma irradiation on melanin productivity was investigated. The maximum melanin yield (3.376 mg/L) was elicited by a stimulus of gamma irradiation at 1.0 kGy. The results evoked that, Curvularia soli AS21 ON076460 melanin exhibited excellent antimicrobial activity against all tested bacteria and fungi. Klebsiella pneumoniae ATCC 13883 and P. digitatum were mostly affected by melanin registering the inhibition zone diameters of 37.51 ± 0.012 and 44.25 ± 0.214 mm, respectively. Moreover, Curvularia soli AS21 ON076460 melanin indicated a significant antiviral efficacy (77% inhibition) of Herpes simplex virus (HSV1). The melanin pigment showed antioxidant activities with IC50 of 42 ± 0.021 and 17 ± 0.02 µg/mL against DPPH and NO, respectively. Melanin had cytotoxic action against human breast cancer and skin cancer cell lines (Mcf7and A431) as well as exerting a low percentage of cell death against normal skin cell lines (Hfb4). Melanin was effective in wound management of human skin cells by 63.04 ± 1.83% compared with control (68.67 ± 1.10%). The novelty in the study is attributed to the possibility of using gamma rays as a safe method in small economic doses to stimulate melanin production from the fungi that have been isolated. In summary, melanin produced from fungi has significant biological activities that encourage its usage as a supportive medical route.

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.

"Structural responses of non-targeted bacterial and hppd communities to the herbicide tembotrione in soil"

Tembotrione (TBT) is a β-triketone herbicide targeting the 4-Hydroxyphenylpyruvate dioxygenase enzyme (4-HPPD) of weeds. This molecule can also affect soil microorganisms, either through both direct and indirect toxic effects for microorganisms expressing 4-HPPD, or by promoting tolerant and/or degrading microbial populations. Our study aimed to characterize the impacts of TBT on the diversity of total- and hppd (coding for 4-HPPD) -soil bacterial communities. Soil microcosms were treated with the active ingredient TBT at the recommended field dose (100 g a.i/ha; D1) or the tenfold dose (D10). Soil samples were collected from 0 to 55 days post-treatment to study: (i) total- and hppd-bacterial diversities using 16SrRNA and hppd amplicons sequencing, respectively; (ii) TBT dissipation in soil. Both total- and hppd-bacterial community composition was not affected by TBT treatments (D1 and D10). However, D10 treatment slightly increased richness and phylogenetic diversity of the total bacterial community while decreasing hppd richness. Overall, the highest dose of TBT seemed to promote TBT-tolerant or TBT-degrading bacterial populations and to deplete TBT-sensitive ones. These effects were transient as TBT was rapidly dissipated with a DT50 of 7 days and 15 days for D1 and D10, respectively. Differential abundance analysis with a Generalized Linear Model allowed the identification of Sphingomonas, Steroidobacter and Lysobacter as genus that were influenced by TBT, and which could be used as a new class of exposure biomarkers.

Microbial Pigments: Major Groups and Industrial Applications

Microbial pigments have many structures and functions with excellent characteristics, such as being biodegradable, non-toxic, and ecologically friendly, constituting an important source of pigments. Industrial production presents a bottleneck in production cost that restricts large-scale commercialization. However, microbial pigments are progressively gaining popularity because of their health advantages. The development of metabolic engineering and cost reduction of the bioprocess using industry by-products opened possibilities for cost and quality improvements in all production phases. We are thus addressing several points related to microbial pigments, including the major classes and structures found, the advantages of use, the biotechnological applications in different industrial sectors, their characteristics, and their impacts on the environment and society.

Can we manage microbial systems to enhance carbon storage?

Climate change is an urgent environmental issue with wide-ranging impacts on ecosystems and society. Microbes are instrumental in maintaining the balance between carbon (C) accumulation and loss in the biosphere, actively regulating greenhouse gas fluxes from vast reservoirs of organic C stored in soils, sediments and oceans. Heterotrophic microbes exhibit varying capacities to access, degrade and metabolise organic C-leading to variations in remineralisation and turnover rates. The present challenge lies in effectively translating this accumulated knowledge into strategies that effectively steer the fate of organic C towards prolonged sequestration. In this article, we discuss three ecological scenarios that offer potential avenues for shaping C turnover rates in the environment. Specifically, we explore the promotion of slow-cycling microbial byproducts, the facilitation of higher carbon use efficiency, and the influence of biotic interactions. The ability to harness and control these processes relies on the integration of ecological principles and management practices, combined with advances in economically viable technologies to effectively manage microbial systems in the environment.

Phenotypic and Genomic Characterization of Streptomyces pakalii sp. nov., a Novel Species with Anti-Biofilm and Anti-Quorum Sensing Activity in ESKAPE Bacteria

The increasing number of infections caused by antimicrobial multi-resistant microorganisms has led to the search for new microorganisms capable of producing novel antibiotics. This work proposes Streptomyces pakalii sp. nov. as a new member of the Streptomycetaceae family. The strain ENCB-J15 was isolated from the jungle soil in Palenque National Park, Chiapas, Mexico. The strain formed pale brown, dry, tough, and buried colonies in the agar with no diffusible pigment in GAE (glucose-asparagine-yeast extract) medium. Scanning electron micrographs showed typical mycelium with long chains of smooth and oval-shaped spores (3-10 m). The strain grew in all of the International Streptomyces Project (ISP)'s media at 28-37 °C with a pH of 6-9 and 0-10% NaCl. S. pakalii ENCB-J15 assimilated diverse carbon as well as organic and inorganic nitrogen sources. The strain also exhibited significant inhibitory activity against the prodigiosin synthesis of Serratia marcescens and the inhibition of the formation and destruction of biofilms of ESKAPE strains of Acinetobacter baumannii and Klebsiella pneumoniae. The draft genome sequencing of ENCB-J15 revealed a 7.6 Mb genome with a high G + C content (71.6%), 6833 total genes, and 6746 genes encoding putative proteins. A total of 26 accessory clusters of proteins associated with carbon sources and amino acid catabolism, DNA modification, and the antibiotic biosynthetic process were annotated. The 16S rRNA gene phylogeny, core-proteome phylogenomic tree, and virtual genome fingerprints support that S. pakalii ENCB-J15 is a new species related to Streptomyces badius and Streptomyces globisporus. Similarly, its average nucleotide identity (ANI) (96.4%), average amino acid identity (AAI) (96.06%), and virtual DNA-DNA hybridization (67.3%) provide evidence to recognize it as a new species. Comparative genomics revealed that S. pakalli and its closest related species maintain a well-conserved genomic synteny. This work proposes Streptomyces pakalii sp. nov. as a novel species that expresses anti-biofilm and anti-quorum sensing activities.

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.

Light effects on Lasiodiplodia theobromae metabolome cultured in vitro

INTRODUCTION

The present work identified and compared intracellular metabolites and metabolic networks in mycelial cultures of Lasiodiplodia theobromae grown under 12 natural light and 24 hours' dark using a 1 H NMR-based metabolomics approach.

MATERIALS AND METHODS

Fungal cultures were grown in potato dextrose media, and metabolites were extracted by sonication with sodium phosphate-buffered saline (pH = 6.0, 10% D2O, 0.1 mM TSP) from mycelium samples collected every week over four weeks.

RESULTS

Multivariate analyses revealed that the light exposure group showed a positive correlation within beta-hydroxybutyrate, acetoacetate, acetone, betaine, choline, glycerol, and phosphocholine. On the other hand, phenyl acetate, leucine, isoleucine, valine, and tyrosine were positively correlated with dark conditions. Light favored the oxidative degradation of valine, leucine, and isoleucine, leading to the accumulation of choline, phosphocholine, betaine, and ketone bodies (ketogenesis). Ketogenesis, gluconeogenesis, and the biosynthesis of choline, phosphocholine, and betaine, were considered discriminatory routes for light conditions. The light-sensing pathways were interlinked with fungal development, as verified by the increased production of mycelia biomass without fruiting bodies and stress signaling, as demonstrated by the increased production of pigments.

AdpAlin regulates lincomycin and melanin biosynthesis by modulating precursors flux in Streptomyces lincolnensis

Lincomycin is one of the most important antibiotics. However, transcriptional regulation network of secondary metabolism in Streptomyces lincolnensis, the lincomycin producer, remained obscure. AdpA from S. lincolnensis (namely AdpAlin) has been proved to activate lincomycin biosynthesis. Here we found that both lincomycin and melanin took l‐tyrosine as precursor, and AdpAlin activated melanin biosynthesis as well. Three tyrosinases, MelC2, MelD2, and MelE, and one tyrosine peroxygenase, LmbB2, participated in lincomycin and melanin biosynthesis in different ways. For melanin biosynthesis, MelC2 was the only key enzyme required. For lincomycin biosynthesis, MelD2 and LmbB2 were positive factors and were suggested to convert l‐tyrosine to l‐dihydroxyphenylalanine (l‐DOPA). Otherwise, MelC2 and MelE were negative factors for lincomycin biosynthesis and they were supposed to oxidize l‐DOPA to generate melanin and certain unknown metabolite, respectively. Based on in silico analysis combined with electrophoretic mobility shift assays (EMSAs), we proved that AdpAlin directly interacted with promoters of melC, melD, and melE by binding to putative AdpA‐binding sites in vitro. Moreover, in vivo experiments revealed that AdpAlin positively regulated the transcription of melC and melE, but negatively regulated melD. In conclusion, AdpAlin was the switch of secondary metabolism in S. lincolnensis, and it modulated precursor flux of lincomycin and melanin biosynthesis by directly activating melC, melE, and lmbB1/lmbB2 or repressing melD.

Evaluation of phytochemicals of Poria cocos against tyrosinase protein: a virtual screening, pharmacoinformatics and molecular dynamics study

Tyrosinase inhibitors are commonly used in the pharmaceutical and cosmetic industries for skin lightening and hypopigmentation. The current inhibitors of tyrosinase induce strong safety concerns which necessitate the discovery of new inhibitors. Natural compounds are a promising solution to discover potential candidate for anti-melanogenic activity as they possess less safety concerns and high therapeutic effect. The current study aimed to screen and identify potential phytochemicals from Poria cocos for tyrosinase inhibition. The phytochemicals were obtained from the Traditional Chinese Medicine System Pharmacology Database and screened for druglikeness score and toxicity class and then subjected to in-silico virtual screening and molecular dynamics. 7,9-(11)-Dehydropachymic acid established hydrogen interaction with the tyrosinase protein and was found to be highly stable as validated with MD simulations. The pharmacokinetic results showed that this compound has adequate toxicity and ADME profile that can be exploited for anti-melanogenic effects. Our study identified 7,9-(11)-dehydropachymic acid as an efficient candidate for tyrosinase inhibition.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03626-8.

Genomes of four Streptomyces strains reveal insights into putative new species and pathogenicity of scab-causing organisms

Genomes of four Streptomyces isolates, two putative new species (Streptomyces sp. JH14 and Streptomyces sp. JH34) and two non thaxtomin-producing pathogens (Streptomyces sp. JH002 and Streptomyces sp. JH010) isolated from potato fields in Colombia were selected to investigate their taxonomic classification, their pathogenicity, and the production of unique secondary metabolites of Streptomycetes inhabiting potato crops in this region. The average nucleotide identity (ANI) value calculated between Streptomyces sp. JH34 and its closest relatives (92.23%) classified this isolate as a new species. However, Streptomyces sp. JH14 could not be classified as a new species due to the lack of genomic data of closely related strains. Phylogenetic analysis based on 231 single-copy core genes, confirmed that the two pathogenic isolates (Streptomyces sp. JH010 and JH002) belong to Streptomyces pratensis and Streptomyces xiamenensis, respectively, are distant from the most well-known pathogenic species, and belong to two different lineages. We did not find orthogroups of protein-coding genes characteristic of scab-causing Streptomycetes shared by all known pathogenic species. Most genes involved in biosynthesis of known virulence factors are not present in the scab-causing isolates (Streptomyces sp. JH002 and Streptomyces sp. JH010). However, Tat-system substrates likely involved in pathogenicity in Streptomyces sp. JH002 and Streptomyces sp. JH010 were identified. Lastly, the presence of a putative mono-ADP-ribosyl transferase, homologous to the virulence factor scabin, was confirmed in Streptomyces sp. JH002. The described pathogenic isolates likely produce virulence factors uncommon in Streptomyces species, including a histidine phosphatase and a metalloprotease potentially produced by Streptomyces sp. JH002, and a pectinesterase, potentially produced by Streptomyces sp. JH010. Biosynthetic gene clusters (BGCs) showed the presence of clusters associated with the synthesis of medicinal compounds and BGCs potentially linked to pathogenicity in Streptomyces sp. JH010 and JH002. Interestingly, BGCs that have not been previously reported were also found. Our findings suggest that the four isolates produce novel secondary metabolites and metabolites with medicinal properties.

Contribution of the Tyrosinase (MoTyr) to Melanin Synthesis, Conidiogenesis, Appressorium Development, and Pathogenicity in Magnaporthe oryzae

Dihydroxynapthalene-(DHN) and L-dihydroxyphenylalanine (L-DOPA) are two types of dominant melanin in fungi. Fungal melanins with versatile functions are frequently associated with pathogenicity and stress tolerance. In rice blast fungus, Magnaporthe oryzae, DHN melanin is essential to maintain the integrity of the infectious structure, appressoria; but the role of the tyrosinase-derived L-DOPA melanin is still unknown. Here, we have genetically and biologically characterized a tyrosinase gene (MoTyr) in M. oryzae. MoTyr encodes a protein of 719 amino acids that contains the typical CuA and CuB domains of tyrosinase. The deletion mutant of MoTyr (ΔMoTyr) was obtained by using a homologous recombination approach. Phenotypic analysis showed that conidiophore stalks and conidia formation was significantly reduced in ΔMoTyr. Under different concentrations of glycerol and PEG, more appressoria collapsed in the mutant strains than in the wild type, suggesting MoTyr is associated with the integrity of the appressorium wall. Melanin measurement confirmed that MoTyr loss resulted in a significant decrease in melanin synthesis. Accordingly, the loss of MoTyr stunted the conidia germination under stress conditions. Importantly, the MoTyr deletion affected both infection and pathogenesis stages. These results suggest that MoTyr, like DHN pigment synthase, plays a key role in conidiophore stalks formation, appressorium integrity, and pathogenesis of M. oryzae, revealing a potential drug target for blast disease control.

Recent Advances and Progress on Melanin: From Source to Application

Melanin is a biological pigment formed by indoles and phenolic compounds. It is widely found in living organisms and has a variety of unique properties. Due to its diverse characteristics and good biocompatibility, melanin has become the focus in the fields of biomedicine, agriculture, the food industry, etc. However, due to the wide range of melanin sources, complex polymerization properties, and low solubility of specific solvents, the specific macromolecular structure and polymerization mechanism of melanin remain unclear, which significantly limits the further study and application of melanin. Its synthesis and degradation pathways are also controversial. In addition, new properties and applications of melanin are constantly being discovered. In this review, we focus on the recent advances in the research of melanin in all aspects. Firstly, the classification, source, and degradation of melanin are summarized. Secondly, a detailed description of the structure, characterization, and properties of melanin is followed. The novel biological activity of melanin and its application is described at the end.

AdpAlin regulates lincomycin and melanin biosynthesis by modulating precursors flux in Streptomyces lincolnensis

Lincomycin is one of the most important antibiotics. However, transcriptional regulation network of secondary metabolism in Streptomyces lincolnensis, the lincomycin producer, remained obscure. AdpA from S. lincolnensis (namely AdpA_lin ) has been proved to activate lincomycin biosynthesis. Here we found that both lincomycin and melanin took l-tyrosine as precursor, and AdpA_lin activated melanin biosynthesis as well. Three tyrosinases, MelC2, MelD2, and MelE, and one tyrosine peroxygenase, LmbB2, participated in lincomycin and melanin biosynthesis in different ways. For melanin biosynthesis, MelC2 was the only key enzyme required. For lincomycin biosynthesis, MelD2 and LmbB2 were positive factors and were suggested to convert l-tyrosine to l-dihydroxyphenylalanine (l-DOPA). Otherwise, MelC2 and MelE were negative factors for lincomycin biosynthesis and they were supposed to oxidize l-DOPA to generate melanin and certain unknown metabolite, respectively. Based on in silico analysis combined with electrophoretic mobility shift assays (EMSAs), we proved that AdpA_lin directly interacted with promoters of melC, melD, and melE by binding to putative AdpA-binding sites in vitro. Moreover, in vivo experiments revealed that AdpA_lin positively regulated the transcription of melC and melE, but negatively regulated melD. In conclusion, AdpA_lin was the switch of secondary metabolism in S. lincolnensis, and it modulated precursor flux of lincomycin and melanin biosynthesis by directly activating melC, melE, and lmbB1/lmbB2 or repressing melD.

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

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

Surface-facilitated formation of polydopamine and its implications in melanogenesis

This manuscript examines influences of differently functionalized surfaces on the formation of solution-dispersed polydopamine (pDA). Glass vials functionalized with different functional groups provided a set of conditions with which the relationship between the area of active surface and the rate of pDA formation could be systematically studied. The results suggest that charged and polar surfaces accelerate pDA formation in solution, with the effect of -NH₂ surfaces being exceptionally strong. In the vials, pDA formed as both forms of dispersions in solution and films at solid-liquid interface. Further analyses confirmed that both forms of pDA formed with -NH₂ surfaces were chemically similar to conventional pDA synthesized without help of functional surfaces. Among short peptide-based amyloid fibers with defined surface functional groups, and those displaying lysines (-NH₂) greatly accelerated the formation of pDA, consistent with the results of -NH₂-functionalized vials. The results suggest that pDA formation may be facilitated by surface functional groups of solid-liquid interfaces, and have implications for the overlooked roles of amyloid fibers in biological melanogenesis.

Characterization of pyomelanin secreted by Shewanella sp. and their application in metal recovery

Melanin is a biopolymer with versatile structural and functional properties and diverse applications in recovering toxic chemicals from water and wastewater, biomedical imaging, and as theragnostic agent. We report the structural characterization and biosynthetic pathway of an extracellular pyomelanin secreted by a sponge-associated bacterium, Shewanella sp. (Shewanella-melanin), and their potential application in metal recovery from liquid. Pyomelanin particles of > 50 µm size were found in the culture medium within 48 h of growth, which were formed through the self-polymerization of benzoquinone molecule produced through homogentisic acid pathway. The aspC and hppD genes involved in the biosynthetic pathway of pyomelanin were detected in the whole genome sequence of Shewanella sp. The FT-IR spectra of Shewanella-melanin, at ~ 3300-3420 cm^-1 corresponding to the stretching vibration of -NH and -OH, was in good agreement with that of Sepia melanin, while its elemental composition (C/N/H/S of 29.2:8.23:6.41:1.58) was unique. Shewanella-melanin showed ~ 300 and ~ 950 times increased chelation of manganese and iron from a liquid medium supplemented with 2 mM of MnSO₄ and FeSO₄, respectively, compared to a control. The FT-IR spectrum showed the binding of metal ions to the carboxylic acid, hydroxyl, and amine groups of Shewanella-melanin. The Shewanella-melanin, with its excellent metal biosorption, could be a potential candidate for removing toxic compounds from water, in turn contributing to the fulfillment of sustainable development goal (SDG) 6.

An extensive review of marine pigments: sources, biotechnological applications, and sustainability

The global demand for food and healthcare products based on natural compounds means that the industrial and scientific sectors are on a continuous search for natural colored compounds that can contribute to the replacement of synthetic colors. Natural pigments are a heterogeneous group of chemical molecules, widely distributed in nature. Recently, the interest in marine organisms has increased as they represent the most varied environment in the world and provide a wide range of colored compounds with bioactive properties and biotechnological applications in areas such as the food, pharmaceutical, cosmetic, and textile industries. The use of marine-derived pigments has increased during the last two decades because they are environmentally safe and healthy compounds. This article provides a comprehensive review of the current knowledge of sources, applications, and sustainability of the most important marine pigments. In addition, alternatives to protect these compounds from environmental conditions and their applications in the industrial sector are reviewed.

Heterologous production and characterization of a pyomelanin of Antarctic Pseudomonas sp. ANT_H4: a metabolite protecting against UV and free radicals, interacting with iron from minerals and exhibiting priming properties toward plant hairy roots

BACKGROUND

Antarctica has one of the most extreme environments in the world. This region is inhabited by specifically adapted microorganisms that produce various unique secondary metabolites (e.g. pigments) enabling their survival under the harsh environmental conditions. It was already shown that these natural, biologically active molecules may find application in various fields of biotechnology.

RESULTS

In this study, a cold-active brown-pigment-producing Pseudomonas sp. ANT_H4 strain was characterized. In-depth genomic analysis combined with the application of a fosmid expression system revealed two different pathways of melanin-like compounds biosynthesis by the ANT_H4 strain. The chromatographic behavior and Fourier-transform infrared spectroscopic analyses allowed for the identification of the extracted melanin-like compound as a pyomelanin. Furthermore, optimization of the production and thorough functional analyses of the pyomelanin were performed to test its usability in biotechnology. It was confirmed that ANT_H4-derived pyomelanin increases the sun protection factor, enables scavenging of free radicals, and interacts with the iron from minerals. Moreover, it was shown for the first time that pyomelanin exhibits priming properties toward Calendula officinalis hairy roots in in vitro cultures.

CONCLUSIONS

Results of the study indicate the significant biotechnological potential of ANT_H4-derived pyomelanin and open opportunities for future applications. Taking into account protective features of analyzed pyomelanin it may be potentially used in medical biotechnology and cosmetology. Especially interesting was showing that pyomelanin exhibits priming properties toward hairy roots, which creates a perspective for its usage for the development of novel and sustainable agrotechnical solutions.

Elucidating the Role of Santalol as a Potent Inhibitor of Tyrosinase: In Vitro and In Silico Approaches

This research work focuses on the potential application of an organic compound, santalol, obtained from santalum album, in the inhibition of the enzyme tyrosinase, which is actively involved in the biosynthesis of melanin pigment. Over-production of melanin causes undesirable pigmentation in humans as well as other organisms and significantly downgrades their aesthetic value. The study is designed to explain the purification of tyrosinase from the mushroom Agaricus bisporus, followed by activity assays and enzyme kinetics to give insight into the santalol-modulated tyrosinase inhibition in a dose-dependent manner. The multi-spectroscopic techniques such as UV-vis, fluorescence, and isothermal calorimetry are employed to deduce the efficiency of santalol as a potential candidate against tyrosinase enzyme activity. Experimental results are further verified by molecular docking. Santalol, derived from the essential oils of santalum album, has been widely used as a remedy for skin disorders and a potion for a fair complexion since ancient times. Based on enzyme kinetics and biophysical characterization, this is the first scientific evidence where santalol inhibits tyrosinase, and santalol may be employed in the agriculture, food, and cosmetic industries to prevent excess melanin formation or browning.

In Living Color: Pigment-Based Microbial Ecology At the Mineral-Air Interface

Pigment-based color is one of the most important phenotypic traits of biofilms at the mineral-air interface (subaerial biofilms, SABs), because it reflects the physiology of the microbial community. Because color is the hallmark of all SABs, we argue that pigment-based color could convey the mechanisms that drive microbial adaptation and coexistence across different terrestrial environments and link phenotypic traits to community fitness and ecological dynamics. Within this framework, we present the most relevant microbial pigments at the mineral-air interface and discuss some of the evolutionary landscapes that necessitate pigments as adaptive strategies for resource allocation and survivability. We report several pigment features that reflect SAB communities' structure and function, as well as pigment ecology in the context of microbial life-history strategies and coexistence theory. Finally, we conclude the study of pigment-based ecology by presenting its potential application and some of the key challenges in the research.

Pleiotropic Effects of Hfq on the Cytochrome c Content and Pyomelanin Production in Shewanella oneidensis

Shewanella oneidensis is the best understood model microorganism for the study of diverse cytochromes (cytos) c that support its unparallel respiratory versatility. Although RNA chaperone Hfq has been implicated in regulation of cyto c production, little is known about the biological pathways that it affects in this bacterium. In this study, from a spontaneous mutant that secretes pyomelanin and has a lowered cyto c content, we identified Hfq to be the regulator that critically associates with both phenotypes in S. oneidensis. We found that expression of the key genes in biosynthesis and degradation of heme is differentially affected by Hfq at under- and overproduced levels, and through modulating heme levels, Hfq influences the cyto c content. Although Hfq in excess results in overproduction of the enzymes responsible for both generation and removal of homogentisic acid (HGA), the precursor of pyomelanin, it is compromised activity of HmgA that leads to excretion and polymerization of HGA to form pyomelanin. We further show that Hfq mediates HmgA activity by lowering intracellular iron content because HmgA is an iron-dependent enzyme. Overall, our work highlights the significance of Hfq-mediated posttranscriptional regulation in the physiology of S. oneidensis, unraveling unexpected mechanisms by which Hfq affects cyto c biosynthesis and pyomelanin production. IMPORTANCE In bacteria, Hfq has been implicated in regulation of diverse biological processes posttranslationally. In S. oneidensis, Hfq affects the content of cytos c that serve as the basis of its respiratory versatility and potential application in bioenergy and bioremediation. In this study, we found that Hfq differentially regulates heme biosynthesis and degradation, leading to altered cyto c contents. Hfq in excess causes a synthetic effect on HmgA, an enzyme responsible for pyomelanin formation. Overall, the data presented manifest that the biological processes in a given bacterium regulated by Hfq are highly complex, amounting to required coordination among multiple physiological aspects to allow cells to respond to environmental changes promptly.

The comparison of biological effects of bacterial and synthetic melanins in neuroblastoma cells

Melanins belong to a group of pigments of different structure and origin. They can be produced synthetically or isolated from living organisms. A number of studies have reported testing of various melanins in neurological studies providing different outcomes. Because the structure of melanins can have an effect on obtained results in cell toxicity studies, we present here our original study which aimed to compare the biological effects of bacterial melanin (biotechnologically obtained from B. thuringiensis) with that of synthetic melanin in neuroblastoma cells. Both melanins were structurally characterized in detail. After melanin treatment (0-200 μg/mL), cell viability, glutathione levels, cell morphology and respiration were assessed in SH-SY5Y cells. The structural analysis showed that bacterial melanin is more hydrophilic according to the presence of larger number of -OH moieties. After melanin treatment, we found that synthetic melanin at similar dosage caused always larger cell impairment compared to bacterial melanin. In addition, more severe toxic effect of synthetic melanin was found in mitochondria. In general, we conclude that more hydrophilic, bacterial melanin induced lower toxicity in neuroblastoma cells in comparison to synthetic melanin. Our findings can be useable for neuroscientific studies estimating the potential use for study of neuroprotection, neuromodulation or neurotoxicity.

Metagenomic shifts in mucus, tissue and skeleton of the coral Balanophyllia europaea living along a natural CO2 gradient

Using the Mediterranean coral Balanophyllia europaea naturally growing along a pH gradient close to Panarea island (Italy) as a model, we explored the role of host-associated microbiomes in coral acclimatization to ocean acidification (OA). Coral samples were collected at three sites along the gradient, mimicking seawater conditions projected for 2100 under different IPCC (The Intergovernmental Panel on Climate Change) scenarios, and mucus, soft tissue and skeleton associated microbiomes were characterized by shotgun metagenomics. According to our findings, OA induced functional changes in the microbiomes genetic potential that could mitigate the sub-optimal environmental conditions at three levels: i. selection of bacteria genetically equipped with functions related to stress resistance; ii. shifts in microbial carbohydrate metabolism from energy production to maintenance of cell membranes and walls integrity; iii. gain of functions able to respond to variations in nitrogen needs at the holobiont level, such as genes devoted to organic nitrogen mobilization. We hence provided hypotheses about the functional role of the coral associated microbiome in favoring host acclimatation to OA, remarking on the importance of considering the crosstalk among all the components of the holobiont to unveil how and to what extent corals will maintain their functionality under forthcoming ocean conditions.

In Silico Interactions of the Components from the Schinus terebinthifolius Extract with Human Tyrosinase

The anti-tyrosinase activity of the leaf extract of Schinus terebinthifolius, also known as Brazilian peppertree, was evaluated using multiple in silico approaches, such as molecular homology, molecular docking, MM-GBSA, molecular dynamics, MM-PBSA, QSAR, and skin permeability predictions. With these computational tools, the compounds that downregulate tyrosinase enzyme activity could be evaluated, and more potent molecules could be identified. The results indicated that various compounds, especially luteolin, are accountable for the anti-tyrosinase activity of S. terebinthifolius. For cosmetic application, further studies with luteolin are especially recommended, for having presented a good performance both in theoretical inhibition (30.92 kJ mol^-1 ) and skin permeability (LogKp=-6.62 cm^-1 ).

Effect of Melanization on Thallus Microstructure in the Lichen Lobaria pulmonaria

Lichens often grow in microhabitats where they experience severe abiotic stresses. Some species respond to high UV radiation by synthesizing dark brown melanic pigments in the upper cortex. However, unlike the melanized structures of non-lichenized fungi, the morphology of the melanic layer in lichens remains unstudied. Here, we analyzed the morphology, ultrastructure, and elemental composition of the melanized layer in UV-exposed thalli of the lichen Lobaria pulmonaria (L.) Hoffm. Using light microscopy, we detected a pigmented layer sensitive to staining with 3,4-L-dihydroxyphenylalanine, a precursor of eumelanin, in the upper cortex of melanized thalli. Analysis of cross-sections of melanized thalli using scanning electron microscopy revealed that melanin-like granules are deposited into the hyphal lumens. Melanized thalli also possessed thicker hyphal cell walls compared to pale thalli. Energy-dispersive X-ray spectroscopy analysis of the elemental composition of the hyphal walls and extracted melanin indicated that the type of melanin synthesized by L. pulmonaria is eumelanin. Transmission electron microscopy was used to show that during melanization melanosome-like dark vesicles are transported to the cell surface and secreted into the cell walls of the fungal hyphae. Results from this study provide new insights into the effects of melanin synthesis on the microstructure of lichen thalli.

Bacterial pigments: A colorful palette reservoir for biotechnological applications

Synthetic derivatives are currently used instead of pigments in many applicative fields, from food to feed, from pharmaceutical to diagnostic, from agronomy to industry. Progress in organic chemistry allowed to obtain rather cheap compounds covering the whole color spectrum. However, several concerns arise from this chemical approach, as it is mainly based on nonrenewable resources such as fossil oil, and the toxicity or carcinogenic properties of products and/or precursors may be harmful for personnel involved in the productive processes. In this scenario, microorganisms and their pigments represent a colorful world to discover and reconsider. Each living bacterial strain may be a source of secondary metabolites with peculiar functions. The aim of this review is to link the physiological role of bacterial pigments with their potential use in different biotechnological fields. This enormous potential supports the big challenge for the development of strategies useful to identify, produce, and purify the right pigment for the desired application. At the end of this ideal journey through the world of bacterial pigments, the attention will be focused on melanin compounds, whose production relies upon different techniques ranging from natural producers, heterologous hosts, or isolated enzymes. In a green workflow, the microorganisms represent the starting and final point of pigment production.

Chemoenzymatic Isolation and Characterization of High Purity Mammalian Melanin

Although melanin is one of the most ubiquitous polymers in living systems, our understanding of its molecular structure, biosynthesis and biophysical properties has been limited to only a small number of organisms other than humans. This is in part due to the difficulty associated with isolating pure melanin. While purification methods exist, they typically involve harsh treatments with strong acid/base conditions combined with elevated temperatures that can lead to the polymer backbone degradation. To be successful, a viable isolation method must deliver a selective, yet complete degradation of non-melanin biopolymers as well as remove small molecule metabolites that are not integrative to the melanin backbone. Here, we demonstrate the use of chemoenzymatic processing guided by fluorescent probes for the purification and isolation of native mammalian melanin without significant induction of chemical degradation. This multi-step purification-tracking methodology enables quantitative isolation of pure melanin from mammalian tissue for spectroscopic characterization.

Melanin biopolymer synthesis using a new melanogenic strain of Flavobacterium kingsejongi and a recombinant strain of Escherichia coli expressing 4-hydroxyphenylpyruvate dioxygenase from F. kingsejongi

BACKGROUND

Melanins are a heterologous group of biopolymeric pigments synthesized by diverse prokaryotes and eukaryotes and are widely utilized as bioactive materials and functional polymers in the biotechnology industry. Here, we report the high-level melanin production using a new melanogenic Flavobacterium kingsejongi strain and a recombinant Escherichia coli overexpressing F. kingsejongi 4-hydroxyphenylpyruvate dioxygenase (HPPD).

RESULTS

Melanin synthesis of F. kingsejongi strain was confirmed via melanin synthesis inhibition test, melanin solubility test, genome analysis, and structural analysis of purified melanin from both wild-type F. kingsejongi and recombinant E. coli expressing F. kingsejongi HPPD. The activity of F. kingsejongi HPPD was demonstrated via in vitro assays with 6 × His-tagged and native forms of HPPD. The specific activity of F. kingsejongi HPPD was 1.2 ± 0.03 μmol homogentisate/min/mg-protein. Bioreactor fermentation of F. kingsejongi produced a large amount of melanin with a titer of 6.07 ± 0.32 g/L, a conversion yield of 60% (0.6 ± 0.03 g melanin per gram tyrosine), and a productivity of 0.03 g/L·h, indicating its potential for industrial melanin production. Additionally, bioreactor fermentation of recombinant E. coli expressing F. kingsejongi HPPD produced melanin at a titer of 3.76 ± 0.30 g/L, a conversion yield of 38% (0.38 ± 0.03 g melanin per gram tyrosine), and a productivity of 0.04 g/L·h.

CONCLUSIONS

Both strains showed sufficiently high fermentation capability to indicate their potential as platform strains for large-scale bacterial melanin production. Furthermore, F. kingsejongi strain could serve as a model to elucidate the regulation of melanin biosynthesis pathway and its networks with other cellular pathways, and to understand the cellular responses of melanin-producing bacteria to environmental changes, including nutrient starvation and other stresses.

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

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

Endophytic Bacteria Colonizing the Petiole of the Desert Plant Zygophyllum dumosum Boiss: Possible Role in Mitigating Stress

Zygophyllum dumosum is a dominant shrub in the Negev Desert whose survival is accomplished by multiple mechanisms including abscission of leaflets to reduce whole plant transpiration while leaving the fleshy, wax-covered petioles alive but dormant during the dry season. Petioles that can survive for two full growing seasons maintain cell component integrity and resume metabolic activity at the beginning of the winter. This remarkable survival prompted us to investigate endophytic bacteria colonizing the internal tissues of the petiole and assess their role in stress tolerance. Twenty-one distinct endophytes were isolated by culturing from surface-sterile petioles and identified by sequencing of the 16S rDNA. Sequence alignments and the phylogenetic tree clustered the isolated endophytes into two phyla, Firmicutes and Actinobacteria. Most isolated endophytes displayed a relatively slow growth on nutrient agar, which was accelerated by adding petiole extracts. Metabolic analysis of selected endophytes showed several common metabolites whose level is affected by petiole extract in a species-dependent manner including phosphoric acid, pyroglutamic acid, and glutamic acid. Other metabolites appear to be endophyte-specific metabolites, such as proline and trehalose, which were implicated in stress tolerance. These results demonstrate the existence of multiple endophytic bacteria colonizing Z. dumosum petioles with the potential role in maintaining cell integrity and functionality via synthesis of multiple beneficial metabolites that mitigate stress and contribute to stress tolerance.

Potential use of bacterial pigments as anticancer drugs and female reproductive toxicity: a review

Abstract Natural bioactive compounds obtained from microorganisms, have awakened particular interest in the industry nowadays. This attention comes when natural resources depletion is pronounced, and the acquisition of both new plant origin resources and bioactive products, represents a challenge for the next generations. In this sense, prospecting for large-scale production and use of bacterial pigments is a necessary strategy for the development of novel products. A wide variety of properties have been attributed to these substances and, among them, their therapeutic potential against important diseases, such as cancer. There is consensus that available chemotherapy protocols are known to detrimentally affect cancer patients fertility. Hence, considerable part of the deleterious effects of chemotherapy is related to the drugs cytotoxicity, which, in addition to cancer cells, also affect normal cells. Therefore, the intrinsic properties of bacterial pigments associated with low cytotoxicity and relevant cell selectivity, certified them as potential anticancer drugs. However, little information is available about reproductive toxicity of these new and promising compounds. Thus, the present review aims to address the main bacterial pigments, their potential uses as anticancer drugs and their possible toxic effects, especially on the female gonad.

Uso potencial de pigmentos bacterianos como drogas anticâncer e toxicidade reprodutiva feminina: uma revisão

Resumo Os compostos bioativos naturais obtidos de microrganismos têm despertado especial interesse da indústria nos últimos anos. Esta atenção ocorre em um momento em que o esgotamento de recursos naturais é pronunciado, e a aquisição de novos insumos e produtos bioativos de origem vegetal representa um desafio para as próximas gerações. Neste sentido, a prospecção para a produção e uso em larga escala dos pigmentos bacterianos tem representado uma importante estratégia para o desenvolvimento de novos produtos. Uma grande variedade de propriedades foi atribuída a estas substâncias, entre elas, o potencial terapêutico contra doenças importantes, como o câncer. Existe um consenso de que os protocolos quimioterápicos disponíveis são conhecidos por afetarem negativamente a fertilidade de pacientes com câncer. Grande parte dos efeitos deletérios da quimioterapia está relacionado à citotoxicidade das drogas usadas para este fim, que além das células cancerosas, afetam as células normais. Nesse sentido, as propriedades naturais atribuídas aos pigmentos bacterianos associadas à baixa citotoxicidade e relevante seletividade, os qualificaram como potenciais drogas anticâncer. No entanto, pouco se tem de informação a respeito da toxicidade reprodutiva destes novos e promissores compostos. Dessa forma, a presente revisão tem o objetivo de abordar os principais pigmentos bacterianos, suas utilizações potenciais como drogas anticâncer, bem como os seus possíveis efeitos tóxicos, sobretudo, sobre a gônada feminina.

Reporter gene-based optoacoustic imaging of E. coli targeted colon cancer in vivo

Bacteria-mediated cancer-targeted therapy is a novel experimental strategy for the treatment of cancers. Bacteria can be engineered to overcome a major challenge of existing therapeutics by differentiating between malignant and healthy tissue. A prerequisite for further development and study of engineered bacteria is a suitable imaging concept which allows bacterial visualization in tissue and monitoring bacterial targeting and proliferation. Optoacoustics (OA) is an evolving technology allowing whole-tumor imaging and thereby direct observation of bacterial colonization in tumor regions. However, bacterial detection using OA is currently hampered by the lack of endogenous contrast or suitable transgene fluorescent labels. Here, we demonstrate improved visualization of cancer-targeting bacteria using OA imaging and E. coli engineered to express tyrosinase, which uses L-tyrosine as the substrate to produce the strong optoacoustic probe melanin in the tumor microenvironment. Tumors of animals injected with tyrosinase-expressing E. coli showed strong melanin signals, allowing to resolve bacterial growth in the tumor over time using multispectral OA tomography (MSOT). MSOT imaging of melanin accumulation in tumors was confirmed by melanin and E. coli staining. Our results demonstrate that using tyrosinase-expressing E. coli enables non-invasive, longitudinal monitoring of bacterial targeting and proliferation in cancer using MSOT.

Phenotypic Characterization and Comparative Genomics of the Melanin-Producing Yeast Exophiala lecanii-corni Reveals a Distinct Stress Tolerance Profile and Reduced Ribosomal Genetic Content

The black yeast Exophiala lecanii-corni of the order Chaetothyriales is notable for its ability to produce abundant quantities of DHN-melanin. While many other Exophiala species are frequent causal agents of human infection, E. lecanii-corni CBS 102400 lacks the thermotolerance requirements that enable pathogenicity, making it appealing for use in targeted functional studies and biotechnological applications. Here, we report the stress tolerance characteristics of E. lecanii-corni, with an emphasis on the influence of melanin on its resistance to various forms of stress. We find that E. lecanii-corni has a distinct stress tolerance profile that includes variation in resistance to temperature, osmotic, and oxidative stress relative to the extremophilic and pathogenic black yeast Exophiala dermatitidis. Notably, the presence of melanin substantially impacts stress resistance in E. lecanii-corni, while this was not found to be the case in E. dermatitidis. The cellular context, therefore, influences the role of melanin in stress protection. In addition, we present a detailed analysis of the E. lecanii-corni genome, revealing key differences in functional genetic content relative to other ascomycetous species, including a significant decrease in abundance of genes encoding ribosomal proteins. In all, this study provides insight into how genetics and physiology may underlie stress tolerance and enhances understanding of the genetic diversity of black yeasts.

Application of bacterial tyrosinases in organic synthesis

Bacterial tyrosinases, as in the case of other bacterial oxidative enzymes, have been found to possess biochemical characteristics that typically make them more suited to applications requiring special operational conditions such as alkaline pH, high or low temperature, the presence of organic solvents, and the presence of inhibitors. Even though a great deal is known about fungal tyrosinases, bacterial tyrosinases still vastly remain underexplored for their potential application in organic synthesis. A literature survey in particular highlights the gaps in our knowledge pertaining to their biochemical properties. Bacterial tyrosinases have not only shown promise in the synthesis of medically important compounds such as L-3,4-dihydroxyphenylalanine (L-DOPA) and melanin but have also seen application in cross-linking reactions of proteins and the polymerization of environmental pollutants. Their ability to catalyse o-hydroxylation reactions have shown some degree of promise in the biocatalytic conversion of resveratrol to piceatannol, tyrosol to hydroxytyrosol, and many more. In this review, we will explore the world of bacterial tyrosinases, their current applications, and future perspectives for the application of these enzymes in organic synthesis.

Pyomelanin-Producing Brevundimonas vitisensis sp. nov., Isolated From Grape (Vitis vinifera L.)

A novel endophytic bacterial strain, designated GR-TSA-9^T, was isolated from surface-sterilized grape (Vitis vinifera L.). 16S rRNA gene sequence analyses showed that the isolate was grouped within the genus Brevundimonas, displaying the highest similarity with Brevundimonas lenta DS-18^T (97.9%) and Brevundimonas kwangchunensis KSL-102^T (97.8%) and less than 97.5% similarity with other members of Brevundimonas. The strain GR-TSA-9^T was a gram negative, rod shaped, facultatively anaerobic, catalase and oxidase positive, and motile bacterium. Its growth occurred at 10–37°C (optimally 25–30°C), at pH 7.0–8.0, and in NaCl 0–1% (optimally 0%). It contained ubiquinone-10 as a respiratory quinone, and the major cellular fatty acids (>10% of the total) were C_16:0 (14.2%) and summed feature 8 (C_18:1ω7c and/or C_18:1ω6c, 65.6%). The polar lipids present in the strain were phosphoglycolipids, phosphatidylglycerol, 1,2-di-O-acyl-3-O-[d-glucopyranosyl-(1→4)-α-d-glucopyranuronosyl]glycerol, and unidentified lipids (L1, L2, and L4). The strain had one 2,976,716bp circular chromosome with a G+C content of 66.4%. The digital DNA–DNA hybridization value between strain GR-TSA-9^T and B. lenta DS-18^T was 20.9%, while the average nucleotide identity value was 76.7%. In addition, the dDDH and ANI values to other members in this genus, whose genome sequences are available, are less than 21.1 and 77.6%. Genome annotation predicted the presence of some gene clusters related to tyrosine degradation and pyomelanin formation. Strain GR-TSA-9^T produced a brown melanin-like pigment in the presence of L-tyrosine-containing media. The highest pigment production (0.19g/L) was observed in tryptic soy broth with 1.0mg/ml L-tyrosine at 25°C for 6days of culture. Biophysical characterization by ultraviolet (UV)–visible spectroscopy, Fourier-transform infrared spectroscopy, and electrospray ionization mass spectrometry confirmed that the pigment was pyomelanin. Additionally, melanized GR-TSA-9^T cells could protect the cells against UVC exposure. The phylogenetic, genomic, phenotypic, and chemotaxonomic features indicated that strain GR-TSA-9^T represents a novel melanin-producing species of Brevundimonas. The type strain was GR-TSA-9^T (KCTC 82386^T=CGMCC 1.18820^T).