Heterologous production of pyomelanin biopolymer using 4-hydroxyphenylpyruvate dioxygenase isolated from Ralstonia pickettii in Escherichia coli

The application of biosurfactant-producing bacteria immobilized in PVA/SA/bentonite bio-composite for hydrocarbon-contaminated soil bioremediation

Oil spills that contaminate the environment can harm the surrounding ecosystem. The oil contains petroleum hydrocarbon which is toxic to the environment hence it needs to be removed. The use of bacteria as remediation media was modified by immobilizing into a matrix hence the bacteria can survive in harsh conditions. In this research, the ability of biosurfactant-producing bacteria (Pseudomonas aeruginosa, Bacillus subtilis, and Ralstonia pickettii) immobilized in the PVA/SA/bentonite matrix was tested in remediation on oil-contaminated soil. The immobilized beads filled with bacteria were added to the original soil sample, as well as washed soil. The beads were characterized by using FTIR and SEM. Based on FTIR analysis, the PVA/SA/bentonite@bacteria beads had similar functional groups compared to each other. SEM analysis showed that the beads had non-smooth structure, while the bacteria were spread outside and agglomerated. Furthermore, GC-MS analysis results showed that immobilized B. subtilis and R. pickettii completely degraded tetratriacontane and heneicosane, respectively. Meanwhile, after soil washing pre-treatment, immobilized bacteria could completely degrade octadecane (P. aeruginosa and R. pickettii) and tetratriacontane (P. aeruginosa and B. subtilis). Based on those results, immobilized bacteria could degrade oil compounds. The degradation result was influenced by the enzymes produced, the ability of the bacteria, the suitability of the test media, and the matrix used. Therefore, this study can be a reference for further soil remediation using eco-friendly methods.

Colored stains: Microbial survey of cellulose-based and lignin rich papers

During the centuries diverse types of paper were produced and were characterized by a different ratio of natural macromolecules, mainly lignin and cellulose. Handmade paper has a higher content of cellulose respect to the early machine-made paper, where the lignin is the other important component. Microorganisms are able to colonize and deteriorate both types of papers. They can release on their surfaces pigments and colorants which produced anesthetic stains. The microbiota colonising 17 stains on handmade and machine-made paper surfaces together with that in library and archive environments was analyzed. Combination of microbiological and high-throughput sequencing (HTS) approaches were applied. The culture-dependent methodology comprised: isolation, DNA identification, hydrolytic and paper staining assays. The HTS was performed by MinION platform and for the mycobiome a more suitable bioinformatics analysis pipeline, MetONTIIME based on QIIME2 framework, was applied. The paper model staining assay permitted the direct recognition of colorizing isolates which in combination with sequencing data evidenced a complex microbial community able to stain the two types of paper. Staining abilities were confirmed by frequently isolated and detected fungi and also by new ones such as Roussoella euonymi and Achaetomium. We have also evidenced the staining ability of several bacteria.

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.

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.

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.

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

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

Bioprocess of Microbial Melanin Production and Isolation

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

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

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

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

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

Unraveling the Structure and Function of Melanin through Synthesis

Melanin is ubiquitous in living organisms across different biological kingdoms of life, making it an important, natural biomaterial. Its presence in nature from microorganisms to higher animals and plants is attributed to the many functions of melanin, including pigmentation, radical scavenging, radiation protection, and thermal regulation. Generally, melanin is classified into five types-eumelanin, pheomelanin, neuromelanin, allomelanin, and pyomelanin-based on the various chemical precursors used in their biosynthesis. Despite its long history of study, the exact chemical makeup of melanin remains unclear, and it moreover has an inherent diversity and complexity of chemical structure, likely including many functions and properties that remain to be identified. Synthetic mimics have begun to play a broader role in unraveling structure and function relationships of natural melanins. In the past decade, polydopamine, which has served as the conventional form of synthetic eumelanin, has dominated the literature on melanin-based materials, while the synthetic analogues of other melanins have received far less attention. In this perspective, we will discuss the synthesis of melanin materials with a special focus beyond polydopamine. We will emphasize efforts to elucidate biosynthetic pathways and structural characterization approaches that can be harnessed to interrogate specific structure-function relationships, including electron paramagnetic resonance (EPR) and solid-state nuclear magnetic resonance (ssNMR) spectroscopy. We believe that this timely Perspective will introduce this class of biopolymer to the broader chemistry community, where we hope to stimulate new opportunities in novel, melanin-based poly-functional synthetic materials.