A Siderophore Mimicking Gelation Component for Capturing and Self-Separation of Fe(III) from an Aqueous Solution of Mixture of Metal Ions

The carbohydrazide-based gelation component N2,N4,N6-(1,3,5-triazine-2,4,6-triyl)tris(benzene-1,3,5-tricarbohydrazide) (CBTC) was synthesized and characterized using various spectroscopic tools. CBTC and trimesic acid (TMA) get self-assembled to form metallogel with Fe3+, specifically through various noncovalent interactions in a DMSO and H2O mixture. The self-assembly shows remarkable specificity toward Fe(III) among different transition metal salts. It is pertinent to point out that the binding specificity for Fe3+ can also be found in nature in the form of siderophores, as they are mainly involved in scavenging iron selectively from the surroundings. DFT studies have been used to investigate the possible interaction between the different components of the iron metallogel. To determine the selectivity of CBTC for iron, CBTC, along with trimesic acid, is used to interact with other metal ions, including Fe(III) ions, in a single system. The gelation components CBTC and TMA selectively bind with iron(III), which leads to the formation of metallogel and gets separated as a discrete layer, leaving the other metal ions in the solution. Therefore, CBTC and TMA together show iron-scavenging properties. This selective scavenging property is explored through FE-SEM, XPS, PXRD, IR, and ICP-AES analysis. The FE-SEM analysis shows a flower-petal-like morphology for the Fe(III) metallogel. The resemblance in the CBTC-TMA-Fe metallogel and metallogel obtained from the mixture of different metal salts is established through FE-SEM images and XPS analysis. The release of iron from the metallogel is achieved with the help of ascorbic acid, which converts Fe3+ to Fe2+. In biological systems, iron also gets released similarly from siderophores. This is the first report where the synthesized gelation component CBTC molecule is capable of scavenging out iron in the form of metallogel and self-separating from the aqueous mixture in the presence of various other metal ions.

Chromophore appended DPA-based copper(II) complexes with a diimine motif towards DNA binding and fragmentation studies

Mixed ligand copper(II) complexes [Cu(L1)(bpy)](ClO4)21 and [Cu(L2)(bpy)](ClO4)22 (where L1 = 1-(anthracen-9-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine, L2 = 1-(pyren-1-yl)-N,N-bis(pyridin-2-ylmethyl)methanamine and bpy = 2,2'-bipyridine) were synthesised and characterised thoroughly via different analytical and spectroscopic techniques i.e., UV-vis spectroscopy, fluorescence spectroscopy, FT-IR spectroscopy, HRMS and EPR spectroscopy. The molecular structures of the synthesised complexes were obtained using the single-crystal X-ray diffraction technique. Both complexes exhibited penta-coordinated and acquired distorted square pyramidal geometry. The redox behaviour of complexes 1 and 2 was investigated by employing cyclic voltammetry. The DNA binding study was carried out by UV-vis spectrophotometry using double-stranded salmon sperm DNA (ds-ss-DNA). The binding constant (Kb) values of 1 and 2 were 0.11 × 104 M-1 and 1.05 × 104 M-1, respectively, which indicates that 2 has better binding ability than 1. This might be due to the higher conjugative abilities with the extended surface area of the aromatic pyrene ring compared to the anthracene moiety. The fluorescence quenching experiments were also performed with EB bound DNA (EB-DNA) and Stern-Volmer constant (KSV) values were calculated as 1.23 × 105 M-1 and 1.39 × 105 M-1 for 1 and 2, respectively, suggesting that 2 showed stronger interaction with ss-DNA than 1. The molecular docking data support the DNA-binding studies, with the sites and mode of interactions against B-DNA varying with 1 and 2. Evaluation of the DNA binding properties of the complexes to linearized plasmid DNA indicated that 2 had modest DNA binding properties, which is a pre-requisite for a genotoxic agent. The effect of 1 and 2 on cell survival was analysed using HeLa cells by MTT assay and it was observed that the IC50 values of 1 and 2 were 43.7 μM and 18.6 μM, respectively. Our study paves the way for the designing of bio-inspired novel mixed metal complexes, which shows promising results for further exploration of molecular and mechanistic studies towards the development of non-platinum based economical metallodrugs.

Genetic Engineering of Talaromyces marneffei to Enhance Siderophore Production and Preliminary Testing for Medical Application Potential

Siderophores are compounds with low molecular weight with a high affinity and specificity for ferric iron, which is produced by bacteria and fungi. Fungal siderophores have been characterized and their feasibility for clinical applications has been investigated. Fungi may be limited in slow growth and low siderophore production; however, they have advantages of high diversity and affinity. Hence, the purpose of this study was to generate a genetically modified strain in Talaromyces marneffei that enhanced siderophore production and to identify the characteristics of siderophore to guide its medical application. SreA is a transcription factor that negatively controls iron acquisition mechanisms. Therefore, we deleted the sreA gene to enhance the siderophore production and found that the null mutant of sreA (ΔsreA) produced a high amount of extracellular siderophores. The produced siderophore was characterized using HPLC-MS, HPLC-DAD, FTIR, and 1H- and 13C-NMR techniques and identified as a coprogen B. The compound showed a powerful iron-binding activity and could reduce labile iron pool levels in iron-loaded hepatocellular carcinoma (Huh7) cells. In addition, the coprogen B showed no toxicity to the Huh7 cells, demonstrating its potential to serve as an ideal iron chelator. Moreover, it inhibits the growth of Candida albicans and Escherichia coli in a dose-dependent manner. Thus, we have generated the siderophore-enhancing strain of T. marneffei, and the coprogen B isolated from this strain could be useful in the development of a new iron-chelating agent or other medical applications.

Comparative Genomics Analysis of Keratin-Degrading Chryseobacterium Species Reveals Their Keratinolytic Potential for Secondary Metabolite Production

A promising keratin-degrading strain from the genus Chryseobacterium (Chryseobacterium sp. KMC2) was investigated using comparative genomic tools against three publicly available reference genomes to reveal the keratinolytic potential for biosynthesis of valuable secondary metabolites. Genomic features and metabolic potential of four species were compared, showing genomic differences but similar functional categories. Eleven different secondary metabolite gene clusters of interest were mined from the four genomes successfully, including five common ones shared across all genomes. Among the common metabolites, we identified gene clusters involved in biosynthesis of flexirubin-type pigment, microviridin, and siderophore, showing remarkable conservation across the four genomes. Unique secondary metabolite gene clusters were also discovered, for example, ladderane from Chryseobacterium sp. KMC2. Additionally, this study provides a more comprehensive understanding of the potential metabolic pathways of keratin utilization in Chryseobacterium sp. KMC2, with the involvement of amino acid metabolism, TCA cycle, glycolysis/gluconeogenesis, propanoate metabolism, and sulfate reduction. This work uncovers the biosynthesis of secondary metabolite gene clusters from four keratinolytic Chryseobacterium species and shades lights on the keratinolytic potential of Chryseobacterium sp. KMC2 from a genome-mining perspective, can provide alternatives to valorize keratinous materials into high-value bioactive natural products.

Present and future of siderophore-based therapeutic and diagnostic approaches in infectious diseases

Iron is an essential micronutrient required for the growth of almost all aerobic organisms; the iron uptake pathway in bacteria therefore represents a possible target for novel antimicrobials, including hybrids between antimicrobials and siderophores. Siderophores are low molecular weight iron chelators that bind to iron and are actively transported inside the cell through specific binding protein complexes. These binding protein complexes are present both in Gram negative bacteria, in their outer and inner membrane, and in Gram positive bacteria in their cytoplasmic membrane. Most bacteria have the ability to produce siderophores in order to survive in environments with limited concentrations of free iron, however some bacteria synthetize natural siderophore-antibiotic conjugates that exploit the siderophore-iron uptake pathway to deliver antibiotics into competing bacterial cells and gain a competitive advantage. This approach has been referred to as a Trojan Horse Strategy. To overcome the increasing global problem of antibiotic resistance in Gram negative bacteria, which often have reduced outer membrane permeability, siderophore-antibiotic hybrid conjugates have been synthetized in vitro. Cefiderocol is the first siderophore-antibiotic conjugate that progressed to late stage clinical development so far. In studies on murine models the iron-siderophore uptake pathway has been also exploited for diagnostic imaging of infectious diseases, in which labelled siderophores have been used as specific probes. The aim of this review is to describe the research progress in the field of siderophore-based therapeutic and diagnostic approaches in infectious diseases.

Overcoming antibiotic resistance: Is siderophore Trojan horse conjugation an answer to evolving resistance in microbial pathogens?

Comparative study of siderophore biosynthesis pathway in pathogens provides potential targets for antibiotics and host drug delivery as a part of computationally feasible microbial therapy. Iron acquisition using siderophore models is an essential and well established model in all microorganisms and microbial infections a known to cause great havoc to both plant and animal. Rapid development of antibiotic resistance in bacterial as well as fungal pathogens has drawn us at a verge where one has to get rid of the traditional way of obstructing pathogen using single or multiple antibiotic/chemical inhibitors or drugs. 'Trojan horse' strategy is an answer to this imperative call where antibiotic are by far sneaked into the pathogenic cell via the siderophore receptors at cell and outer membrane. This antibiotic once gets inside, generates a 'black hole' scenario within the opportunistic pathogens via iron scarcity. For pathogens whose siderophore are not compatible to smuggle drug due to their complex conformation and stiff valence bonds, there is another approach. By means of the siderophore biosynthesis pathways, potential targets for inhibition of these siderophores in pathogenic bacteria could be achieved and thus control pathogenic virulence. Method to design artificial exogenous siderophores for pathogens that would compete and succeed the battle of intake is also covered with this review. These manipulated siderophore would enter pathogenic cell like any other siderophore but will not disperse iron due to which iron inadequacy and hence pathogens control be accomplished. The aim of this review is to offer strategies to overcome the microbial infections/pathogens using siderophore.

Synthesis, nature and utility of universal iron chelator - Siderophore: A review

Siderophores, the secondary metabolite of various microorganisms are ferric ion specific chelators secreted under iron stressed condition. These non-ribosomal peptides have been classified as catecholate, hydroxamate, carboxylate and mixed types. Recent studies focus on discovery of possible mammalian siderophores. The biosynthesis pathway including non-ribosomal dependent as well as non-ribosomal independent pathways are of great interest now a days. Many significant roles of siderophores such as virulence in pathogens, oxidative stress tolerance, classification of organisms etc. are being discovered. Studies on siderophore utilization in bioremediation and other heavy metal chelation have increased in past decade. The iron chelation ability of siderophores is being recently studied with regards to malignant cancerous cells. Not only this, it has been found that they possess antimicrobial properties which can be utilized against number of microbes. This review covers all recent aspects of siderophore and its applications.

High Antibacterial Activity of Functionalized Chemically Exfoliated MoS2

In view of the implications of inherent resistance of pathogenic bacteria, especially ESKAPE pathogens toward most of the commercially available antibiotics and the importance of these bacteria-induced biofilm formation leading to chronic infection, it is important to develop new-generation synthetic materials with greater efficacy toward antibacterial property. In addressing this issue, this paper reports a proof-of-principle study to evaluate the potential of functionalized two-dimensional chemically exfoliated MoS₂ (ce-MoS₂) toward inhibitory and bactericidal property against two representative ESKAPE pathogenic strain-a Gram-positive Staphylococcus aureus (MRSA) and a Gram-negative Pseudomonas aeruginosa. More significantly, the mechanistic study establishes a different extent of oxidative stress together with rapid membrane depolarization in contact with ce-MoS₂ having ligands of varied charge and hydrophobicity. The implication of our results is discussed in the light of the lack of survivability of planktonic bacteria and biofilm destruction in vitro. A comparison with widely used small molecules and other nanomaterial-based therapeutics conclusively establishes a better efficacy of 2D ce-MoS₂ as a new class of antibiotics.

Engineered biomaterial and biophysical stimulation as combinatorial strategies to address prosthetic infection by pathogenic bacteria

A plethora of antimicrobial strategies are being developed to address prosthetic infection. The currently available methods for implant infection treatment include the use of antibiotics and revision surgery. Among the bacterial strains, Staphylococcus species pose significant challenges particularly, with regard to hospital acquired infections. In order to combat such life threatening infectious diseases, researchers have developed implantable biomaterials incorporating nanoparticles, antimicrobial reinforcements, surface coatings, slippery/non-adhesive and contact killing surfaces. This review discusses a few of the biomaterial and biophysical antimicrobial strategies, which are in the developmental stage and actively being pursued by several research groups. The clinical efficacy of biophysical stimulation methods such as ultrasound, electric and magnetic field treatments against prosthetic infection depends critically on the stimulation protocol and parameters of the treatment modality. A common thread among the three biophysical stimulation methods is the mechanism of bactericidal action, which is centered on biophysical rupture of bacterial membranes, the generation of reactive oxygen species (ROS) and bacterial membrane depolarization evoked by the interference of essential ion-transport. Although the extent of antimicrobial effect, normally achieved through biophysical stimulation protocol is insufficient to warrant therapeutic application, a combination of antibiotic/ROS inducing agents and biophysical stimulation methods can elicit a clinically relevant reduction in viable bacterial numbers. In this review, we present a detailed account of both the biomaterial and biophysical approaches for achieving maximum bacterial inactivation. Summarizing, the biophysical stimulation methods in a combinatorial manner with material based strategies can be a more potent solution to control bacterial infections. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 2174-2190, 2017.