Biofilm Formation and Heat Stress Induce Pyomelanin Production in Deep-Sea Pseudoalteromonas sp. SM9913

Amorosia littoralis Mantle & D. Hawksw. survives as root endophyte of mangroves and produces water soluble melanin pigment

Melanins are heterogenous biopolymers produced by many macro and microorganisms. They enhance the ecological fitness of the producer organisms by improving their virulence and protecting them from radiation, osmotic and heat stresses. Fungi synthesise either DOPA or DHN melanin and deposit them on their cell walls. Some fungal isolates produce water soluble melanin (pyomelanin) which is excerted out of the hyphae into the surrounding environment. Pyomelanin, a polymer of homogentisate, exhibits antimicrobial, UV screening, antioxidative, and anti-inflammatory activities and recent studies also show that pyomelanin could find use in space travel as radiation shield. However, scant literature is available on fungi with ability to produce pyomelanin. We report for the first time that Amorosia littoralis occurs as a root endophyte in mangrove species including Avicennia marina, Bruguiera cylindrica and Bruguiera gymnorhiza and produces pyomelanin. Considering the various technological uses of pyomelanin, this study underscores the need to explore fungi of different habitats to identify hyperproducers and to obtain chemically diverse pyomelanin.

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.

Deciphering mechanisms of production of natural compounds using inducer-producer microbial consortia

Living organisms produce a wide range of metabolites. Because of their potential antibacterial, antifungal, antiviral, or cytostatic properties, such natural molecules are of high interest to the pharmaceutical industry. In nature, these metabolites are often synthesized via secondary metabolic biosynthetic gene clusters that are silent under the typical culturing conditions. Among different techniques used to activate these silent gene clusters, co-culturing of "producer" species with specific "inducer" microbes is a particularly appealing approach due to its simplicity. Although several "inducer-producer" microbial consortia have been reported in the literature and hundreds of different secondary metabolites with attractive biopharmaceutical properties have been described as a result of co-cultivating inducer-producer consortia, less attention has been devoted to the understanding of the mechanisms and possible means of induction for production of secondary metabolites in co-cultures. This lack of understanding of fundamental biological functions and inter-species interactions significantly limits the diversity and yield of valuable compounds using biological engineering tools. In this review, we summarize and categorize the known physiological mechanisms of production of secondary metabolites in inducer-producer consortia, and then discuss approaches that could be exploited to optimize the discovery and production of secondary metabolites.

In Vitro and In Vivo Biocompatibility of Natural and Synthetic Pseudomonas aeruginosa Pyomelanin for Potential Biomedical Applications

Bacteria are the source of many bioactive compounds, including polymers with various physiological functions and the potential for medical applications. Pyomelanin from Pseudomonas aeruginosa, a nonfermenting Gram-negative bacterium, is a black-brown negatively charged extracellular polymer of homogentisic acid produced during L-tyrosine catabolism. Due to its chemical properties and the presence of active functional groups, pyomelanin is a candidate for the development of new antioxidant, antimicrobial and immunomodulatory formulations. This work aimed to obtain bacterial water-soluble (Pyo_sol), water-insoluble (Pyo_insol) and synthetic (sPyo) pyomelanin variants and characterize their chemical structure, thermosensitivity and biosafety in vitro and in vivo (Galleria mallonella). FTIR analysis showed that aromatic ring connections in the polymer chains were dominant in Pyo_sol and sPyo, whereas Pyo_insol had fewer C_ar-C_ar links between rings. The differences in chemical structure influence the solubility of various forms of pyomelanins, their thermal stability and biological activity. Pyo_sol and Pyo_insol showed higher biological safety than sPyo. The obtained results qualify Pyo_sol and Pyo_insol for evaluation of their antimicrobial, immunomodulatory and proregenerative activities.

Characterization of Physicochemical Properties of Melanin Produced by Gluconobacter oxydans FBFS 97

The present study aimed to characterize melanin pigment extracted from Gluconobacter oxydans FBFS 97. After 14 days of culture at 28 °C in GY (glucose and yeast extract) liquid-state medium, G. oxydans FBFS97 produce the maximum melanin, up to about 12–15 mg/L. The physicochemical characteristics of the extracted melanin showed an ability to dissolve in 1 mol/L NaOH or 1 mol/L KOH, and insolubility in water and most organic solvents, such as chloroform and petroleum ether. The extracted melanin was confirmed to be exact melanin by ultraviolet-visible spectrophotometry, Fourier-transform infrared spectroscopy, thin-layer chromatography, elemental analysis, and scanning electron microscopy. The UV-visible spectrum of G. oxydans FBFS97 exhibited a maximum absorption peak at 230 nm. Extracted melanin demonstrated significant free radical-scavenging activity by DPPH and ABTS methods. The IC50 value of the extracted melanin for scavenging 50% DPPH radicals was 36.94 μg/mL, and the IC50 value of antioxidant activity for ABTS was 4.06 μg/mL. Hence, G. oxydans FBFS97 has the potential to be a new candidate for melanin production.

Vibrio splendidus virulence to Apostichopus japonicus is mediated by hppD through glutamate metabolism and flagellum assembly

Vibrio splendidus is the main opportunistic pathogen that causes skin ulcer syndrome in Apostichopus japonicus. hppDIn the present study, mutant V. splendidus with an in-frame deletion of hppDV.s. (MTVs) was constructed. The median lethal doses of wild-type V. splendidus (WTVs) and MTVs were 5.129 × 10⁶ and 2.606 × 10¹⁰ CFU mL⁻¹, respectively. RNA-Seq was performed using WTVs and MTVs cells at different growth stages to explore the mechanisms of the pathogenesis mediated by hppDV.s. Gene Ontology analysis showed that the expression levels of 105 genes involved in amino acid metabolism and protein binding were remarkably different between MTVs and WTVs. Kyoto Encyclopedia of Genes and Genomes analysis showed that the pathways of glutamate metabolism and flagellum assembly involved in biofilm formation and swarming motility were suppressed in MTVs. Correspondingly, the swarming motility, biofilm formation and colonisation of MTVs were remarkably decreased compared with those of WTVs. The results showed that 4-hppD catalyses tyrosine into fumarate, which could enhance glutamate metabolism and ATP production; promote flagellum assembly through the TCA cycle and lead to higher swarming, biofilm formation and colonisation abilities, to contribute to the pathogenesis of V. splendidus.

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

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

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

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

A Review of Microalgal Biofilm Technologies: Definition, Applications, Settings and Analysis

Biofilm-based algal cultivation has many advantages over the conventional suspended growth methods and has received increased attention as a potential platform for algal production, wastewater treatment (nutrient removal), and a potential pathway to supply feedstock for microalgae-based biorefinery attempts. However, the attached cultivation by definition and application is a result of a complex interaction between the biotic and abiotic components involved. Therefore, the entire understanding of the biofilm nature is still a research challenge due to the need for real-time analysis of the system. In this review, the state of the art of biofilm definition, its life cycle, the proposed designs of bioreactors, screening of carrier materials, and non-destructive techniques for the study of biofilm formation and performance are summarized. Perspectives for future research needs are also discussed to provide a primary reference for the further development of microalgal biofilm systems.

Antagonistic Roles of Gallates and Ascorbic Acid in Pyomelanin Biosynthesis of Pseudomonas aeruginosa Biofilms

Primarily synthesized for chelating metal ions from the surrounding media, the pyomelanin plays an important role in bacterial virulence where it is needed for infection and biofilm formation as well as protection from host immune response. In this study, two out of three phenolic acids, gallic acid, and propyl gallate induced pyomelanin in two clinical isolates of Pseudomonas aeruginosa and inhibited biofilm formation. Ascorbic acid treatment reversed the gallic acid and propyl gallate mediated pyomelanin synthesis without reversing the inhibition of the biofilm formation. mRNA expression study revealed the upregulation of homogentisic acid oxidase enzyme by ascorbic acid treatment, possibly contributing towards the inhibition of pyomelanin synthesis. Tannic acid did not show any antibacterial or pyomelanin-induction activities. The synergistic effect of gallates and ascorbic acid in the inhibition of biofilm formation and associated pyomelanin synthesis was evidenced which needs further studies to establish their antibacterial efficacies, especially against the clinical isolates of Pseudomonas sp.

Novel arsenic hyper-resistant bacteria from an extreme environment, Crven Dol mine, Allchar, North Macedonia

Novel hyper-resistant bacteria were isolated from the Crven Dol mine (Allchar, North Macedonia), arsenic-rich extreme environment. Bacteria were recovered from a secondary mineral mixture, an alteration of hydrothermal realgar rich in arsenates (pharmacolite, hornesite, and talmessite). The sample was recovered from the dark part of the mine at 28 m depth. Three bacterial strains and a bacterial consortium were isolated for their capacity to survive exposure to 32 g/L (209 mM) of arsenite, and 176 g/L (564 mM) of arsenate. The 16S rRNA gene analysis identified bacterial isolates as Stenotrophomonas sp. and two Microbacterium spp. This analysis also revealed that bacterial consortium comprise two Bacteriodetes exhibiting similarity to Olivibacter ginsengisoli and to uncultured bacterium, and one γ-proteobacteria with similarity to Luteimonas sp. Among all isolates Stenotrophomonas sp. exhibited the highest tolerance to As compound as well as the capacity to accumulate As inside the cells. Analysis of genes involved in As-resistance showed that recovered isolates possess the genes encoding the ArsB, Acr3(1) and Acr3(2) proteins, indicating that at least a part of their resistance could be ascribed to As-efflux systems described in isolates obtained from human-polluted environments.

Pyomelanin biosynthetic pathway in pigment-producer strains from the pandemic Acinetobacter baumannii IC-5

BACKGROUND

Acinetobacter baumannii outbreaks have been associated with pandemic International Clones (ICs), but the virulence factors involved with their pathogenicity are sparsely understood. Pigment production has been linked with bacterial pathogenicity, however, this phenotype is rarely observed in A. baumannii.

OBJECTIVES

This study aimed to characterise the reddish-brown pigment produced by A. baumannii strains, and to determine its biosynthetic pathway by genomic approaches.

METHODS

Pigment characterisation and antimicrobial susceptibility were conducted by phenotypic tests. The clonal relationship was obtained by pulsed field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST). The genome of an A. baumannii was obtained for characterisation of genes involved with pigment production.

FINDINGS

The pyomelanin was the pigment produced by A. baumannii. Strains were extensively drug resistant and belonged to the IC-5/ST79. The pyomelanin biosynthetic pathway was determined and presented a particular architecture concerning the peripheral (tyrB, phhB and hpd) and central (hmgB, hmgC and hmgR) metabolic pathway genes. The identification of a distant HmgA homologue, probably without dioxygenase activity, could explain pyomelanin production. Virulence determinants involved with adherence (csuA/BABCDE and a T5bSS-carrying genomic island), and iron uptake (basABCDEFGHIJ, bauABCDEF and barAB) were characterised.

MAIN CONCLUSION

There is a biosynthetic pathway compatible with the pyomelanin production observed in persistent A. baumannii IC-5 strains.

Melanin biosynthesis in bacteria, regulation and production perspectives

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

Advances in microbial culturing conditions to activate silent biosynthetic gene clusters for novel metabolite production

Natural products (NPs) produced by bacteria and fungi are often used as therapeutic agents due to their complex structures and wide range of bioactivities. Enzymes that build NPs are encoded by co-localized biosynthetic gene clusters (BGCs), and genome sequencing has recently revealed that many BGCs are “silent” under standard laboratory conditions. There are numerous methods used to activate “silent” BGCs that rely either upon altering culture conditions or genetic modification. In this review, we discuss several recent microbial cultivation methods that have been used to expand the scope of NPs accessible in the laboratory. These approaches are divided into three categories: addition of a physical scaffold, addition of small molecule elicitors, and co-cultivation with another microbe.

Culture dependent and independent analysis and appraisal of early stage biofilm-forming bacterial community composition in the Southern coastal seawater of India

Microbial aggregation on artificial surfaces is a fundamental phenomenon in aquatic systems that lead to biofouling, corrosion and influence the buoyancy of plastic materials. Despite the maritime activities and with nearshore large industrial sector, Laccadive Sea in the Indian Ocean has rarely been investigated for characterizing early biofilm-forming bacterial community. The present investigation was aimed to catalogue the primary colonizers on artificial surfaces and their comparison with planktonic community in southern coastal seawater of India. Surface seawater samples and biofilm assembled on three artificial surfaces over a period of 72 h of immersion in the intake area of a nuclear power plant at Kudankulam, India were collected. The structure of surface assemblages and plankton were unveiled by employing culture dependent, DGGE and NGS methods. In static condition, a collection of aerobic heterotrophic bacteria was screened in vitro for their ability to form potent biofilm. Proteobacteria preponderated the communities both in seawater and natural biofilm and Gammaproteobacteria accounted for >85% in the latter. Vibrionaceae, Alteromonadaceae and Pseudoalteromonadaceae dominated the biofilm community and constituted for 41, 25 and 8%, respectively. In contrast to other studies that showed Rhodobacteraceae family of Alphaproteobacteria as predominant component, we found Vibrionaceae of Gammaproteobacteria as dominant group in early stage of biofilm formation. Both DGGE and NGS data indicated that the attached community is noticeably distinct from those suspended in water column and form the basis for the proposed hypothesis of species sorting theory, that is, the local environmental conditions influence bacterial community assembly. Collectively, the data are testament for species sorting process that occur during initial assembly of bacterial community in marine environment and shed light on the structure of marine bacterial biofilm development. The outcome of the present study is of immense importance for designing long-term, efficient and appropriate strategies to control the biofouling phenomenon.

Single Amino Acid Substitution in Homogentisate Dioxygenase Affects Melanin Production in Bacillus thuringiensis

Bacillus thuringiensis formulation losing its activity under field conditions due to UV radiation and photoprotection of B. thuringiensis based on melanin has attracted the attention of researchers for many years. Here, a single amino acid substitution (G272E) in homogentisate 1,2-dioxygenase was found to be responsible for pigment overproduction in B. thuringiensis BMB181, a derivative of BMB171. Disrupting the gene encoding homogentisate dioxygenase in BMB171 induced the accumulation of the homogentisic acid and provoked an increased pigment formation. To gain insights into homogentisate 1,2-dioxygenase in B. thuringiensis, we constructed a total of 14 mutations with a single amino acid substitution, and six of the mutant proteins were found to affect the melanin production when substituted by alanine. This study provides a new way to construct pigment-overproducing strains by impairing the homogentisate dioxygenase with a single mutation in B. thuringiensis, and the findings will facilitate a better understanding of this enzyme.