Antimalarial activity of natural and synthetic prodiginines

Serratia marcescens ATCC 274 increases production of the red pigment prodigiosin in response to Chi phage infection

Serratia marcescens is an opportunistic human pathogen that produces a vibrant red pigment called prodigiosin. Prodigiosin has implications in virulence of S. marcescens and promising clinical applications. We discovered that addition of the virulent flagellotropic bacteriophage χ (Chi) to a culture of S. marcescens stimulates a greater than fivefold overproduction of prodigiosin. Active phage infection is required for the effect, as a χ-resistant strain lacking flagella does not respond to phage presence. Via a reporter fusion assay, we have determined that the addition of a χ-induced S. marcescens cell lysate to an uninfected culture causes a threefold increase in transcription of the pig operon, containing genes essential for pigment biosynthesis. Replacement of the pig promoter with a constitutive promoter abolished the pigmentation increase, indicating that regulatory elements present in the pig promoter likely mediate the phenomenon. We hypothesize that S. marcescens detects the threat of phage-mediated cell death and reacts by producing prodigiosin as a stress response. Our findings are of clinical significance for two main reasons: (i) elucidating complex phage-host interactions is crucial for development of therapeutic phage treatments, and (ii) overproduction of prodigiosin in response to phage could be exploited for its biosynthesis and use as a pharmaceutical.

Discovery and Optimization of Tambjamines as a Novel Class of Antileishmanial Agents

Leishmaniasis is a neglected tropical disease that is estimated to afflict over 12 million people. Current drugs for leishmaniasis suffer from serious deficiencies, including toxicity, high cost, modest efficacy, primarily parenteral delivery, and emergence of widespread resistance. We have discovered and developed a natural product-inspired tambjamine chemotype, known to be effective against Plasmodium spp, as a novel class of antileishmanial agents. Herein, we report in vitro and in vivo antileishmanial activities, detailed structure-activity relationships, and metabolic/pharmacokinetic profiles of a large library of tambjamines. A number of tambjamines exhibited excellent potency against both Leishmania mexicana and Leishmania donovani parasites with good safety and metabolic profiles. Notably, tambjamine 110 offered excellent potency and provided partial protection to leishmania-infected mice at 40 and/or 60 mg/kg/10 days of oral treatment. This study presents the first account of antileishmanial activity in the tambjamine family and paves the way for the generation of new oral antileishmanial drugs.

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.

Pyrrole: A Decisive Scaffold for the Development of Therapeutic Agents and Structure-Activity Relationship

An overview of pyrroles as distinct scaffolds with therapeutic potential and the significance of pyrrole derivatives for drug development are provided in this article. It lists instances of naturally occurring pyrrole-containing compounds and describes the sources of pyrroles in nature, including plants and microbes. It also explains the many conventional and modern synthetic methods used to produce pyrroles. The key topics are the biological characteristics, pharmacological behavior, and functional alterations displayed by pyrrole derivatives. It also details how pyrroles are used to treat infectious diseases. It describes infectious disorders resistant to standard treatments and discusses the function of compounds containing pyrroles in combating infectious diseases. Furthermore, the review covers the uses of pyrrole derivatives in treating non-infectious diseases and resistance mechanisms in non-infectious illnesses like cancer, diabetes, and Alzheimer's and Parkinson's diseases. The important discoveries and probable avenues for pyrrole research are finally summarized, along with their significance for medicinal chemists and drug development. A reference from the last two decades is included in this review.

Identification of Novel Protein Targets of Prodigiosin for Breast Cancer Using Inverse Virtual Screening Methods

Prodigiosin (PG) is chemically formulated as 4-methoxy-5-[(5-methyl-4-pentyl-2H-pyrrol-2ylidene)methyl]-2,2'-bi-1H-pyrrole and it is an apoptotic agent. Only a few protein targets for PG have been identified so far for regulating various diseases; nevertheless, finding more PG targets is crucial for novel drug discovery research. A bioinformatics method was applied in this work to find additional potential PG targets. Initially, a text mining analysis was conducted to determine the relationship between PG and a variety of metabolic processes. One hundred sixteen proteins from the KEGG pathway were selected for the docking study. Inverse virtual screening was performed by Discovery Studio software 4.1 using CHARMm-based docking tool. Twelve proteins are screened out of 116 because their CDOCKER interaction energy is larger than - 40.22 kcal/mol. The best docking score with PG was reported to be - 44.25 kcal/mol, - 44.99 kcal/mol, and - 40.91 kcal/mol for three novel proteins, such as human epidermal growth factor-2 (HER-2), mitogen-activated protein kinase (MEK), and S6 kinase protein (S6K) respectively. The interactions in the S6K/PG complex are predominantly hydrophobic; however, hydrogen bond interactions can be identified in the MEK/PG and HER-2/PG complexes. The root-mean-square deviation (RMSD) and key interaction score system (KISS) were further used to validate the docking approach. The docking approach employed in this work has a low RMSD value (2.44 Å) and a high KISS score (0.5), indicating that it is significant.

Multicopy expression of sigma factor RpoH reduces prodigiosin biosynthesis in Serratia marcescens FS14

Regulation of prodigiosin biosynthesis is received wide attention due to the antimicrobial, immunosuppressive and anticancer activities of prodigiosin. Here, we constructed a transposon mutant library in S. marcescens FS14 to identify genes involved in the regulation of prodigiosin biosynthesis. 62 strains with apparently different colors were obtained. Identification of the transposon insertion sites revealed that they are classified into three groups: the coding region of cyaA and two component system eepS/R and the promoter region of rpoH. Since the effect of cyaA and eepS/R genes on prodigiosin was extensively investigated in Serratia marcescens, we chose the mutant of rpoH for further investigation. Further deletion mutation of rpoH gene showed no effect on prodigiosin production suggesting that the effect on prodigiosin production caused by transposon insertion is not due to the deletion of RpoH. We further demonstrated that multicopy expression of RpoH reduced prodigiosin biosynthesis indicating that transposon insertion caused RpoH enhanced expression. Previous results indicate that RpoS is the sigma factor for transcription of pig gene cluster in FS14, to test whether the enhanced expression of RpoH prevents prodigiosin by competing with RpoS, we found that multicopy expression of RpoS could alleviate the prodigiosin production inhibition by enhanced RpoH. We proposed that multicopy expressed RpoH competes with RpoS for core RNA polymerase (RNAP) resulting in decreased transcription of pig gene cluster and prodigiosin production reduction. We also demonstrated that RpoH is not directly involved in prodigiosin biosynthesis. Our results suggest that manipulating the transcription level of sigma factors may be applied to regulate the production of secondary metabolites.

Comparative study on the toxic effects of secondary nanoplastics from biodegradable and conventional plastics on Streptomyces coelicolor M145

Because of the excellent properties, plastics have been widely used in the past decades and caused serious environmental issues. As an excellent substitute for conventional plastics, the biodegradable plastics have attracted increasing attention. However, biodegradable plastics may produce more micro/nanoplastics in the short time compared with conventional plastics, and cause more serious ecological risks. In this study, the short-term toxicity of nanoplastics released from biodegradable and conventional plastics on Streptomyces coelicolor M145 was investigated. After 30 days of degradation, the biodegradable microplastics, polylactic acid (PLA) and polyhydroxyalkanoates (PHA) released more secondary nanoplastics than conventional microplastics, polystyrene (PS). After exposure, PLA and PHA nanoplastics showed significant toxicity to M145. The survival rate of M145 cells was 16.1% after treatment with PLA nanoplastics for 7 days (PLA-7). The toxicity of PHA was lower than that of PLA. This might have been due to the agglomeration of PHA nanoplastics in the solution. Compared with the controls, the PS secondary nanoplastics showed no significant toxicity to M145. After the treatment, the production of antibiotics, actinorhodin (ACT) and undecylprodigiosin (RED), significantly increased. The yields of ACT and RED reached their maximum values after treatment with PLA-7, which were 4.2-fold and 2.1-fold higher than those of the controls, respectively. The addition of biodegradable nanoplastics significantly increased the expression of these key pathway-specific regulatory genes, leading to increased antibiotic production. This study provides toxicological insights into the impacts of conventional and biodegradable microplastics on S. coelicolor.

Isolation, Identification, and Antibacterial Properties of Prodigiosin, a Bioactive Product Produced by a New Serratia marcescens JSSCPM1 Strain: Exploring the Biosynthetic Gene Clusters of Serratia Species for Biological Applications

Prodigiosin pigment has high medicinal value, so exploring this compound is a top priority. This report presents a prodigiosin bioactive compound isolated from Serratia marcescens JSSCPM1, a new strain. The purification process of this compound involves the application of different chromatographic methods, including UV-visible spectroscopy, high-performance liquid chromatography (HPLC), and liquid chromatography-mass spectrometry (LC/MS). Subsequent analysis was performed using nuclear magnetic resonance (NMR) to achieve a deeper understanding of the compound's structure. Finally, through a comprehensive review of the existing literature, the structural composition of the isolated bioactive compound was found to correspond to that of the well-known compound prodigiosin. The isolated prodigiosin compound was screened for antibacterial activity against both Gram-positive and Gram-negative bacteria. The compound inhibited the growth of Gram-negative bacterial strains compared with Gram-positive bacterial strains. It showed a maximum minimum inhibitory concentration against Escherichia coli NCIM 2065 at a 15.9 ± 0.31 μg/mL concentration. The potential binding capabilities between prodigiosin and the OmpF porin proteins (4GCS, 4GCP, and 4GCQ) were determined using in silico studies, which are generally the primary targets of different antibiotics. Comparative molecular docking analysis indicated that prodigiosin exhibits a good binding affinity toward these selected drug targets.

PtrA regulates prodigiosin synthesis and biological functions in Serratia marcescens FZSF02

Serratia marcescens is a gram-negative bacterium that is able to produce many secondary metabolites, such as the prominent red pigment prodigiosin (PG). In this work, a ptrA-disrupted mutant strain with reduced PG production was selected from Tn5 transposon mutants. RT-qPCR results indicated that ptrA promoted elevated transcription of the pig gene cluster in S. marcescens FZSF02. Furthermore, we found that ptrA also controls several other important biological functions of S. marcescens, including swimming and swarming motilities, biofilm formation, hemolytic activity, and stress tolerance. In conclusion, this study demonstrates that ptrA is a PG synthesis-promoting factor in S. marcescens and provides a brief understanding of the regulatory mechanism of ptrA in S. marcescens cell motility and hemolytic activity.

Prodigiosin from Serratia rubidaea MJ 24 impedes Helicoverpa armigera development by the dysregulation of Juvenile hormone-dopamine system

Prodigiosin pigment is a secondary metabolite produced by many bacterial species and is known for its medicinal properties. A few of these prodigiosin-producing bacteria are also reported to be entomopathogenic. It is intriguing to unravel the role of prodigiosin in insecticidal activities and its mode of action. In this study, we have shown the production and characterization of prodigiosin from the Serratia rubidaea MJ 24 isolated from the soil of the Western Ghats, India. Further, we assessed the effect of this pigment on the lepidopteran agricultural pest, Helicoverpa armigera. Prodigiosin-fed H. armigera indicated defective development of insect growth upon treatment. Due to defective early development, about 50% mortality and 40% reduction in body weight were observed in insects fed on a 500 ppm prodigiosin-containing diet. The transcriptomic analysis of these insects indicated significant dysregulation of Juvenile hormone synthesis and response related genes. In addition, dopamine related processes and their resultant melanization and sclerotization processes were also found to be affected. The changes in the expression levels of the key transcripts were further validated using real-time quantitative PCR. The metabolome data confirmed the developmental dysregulation of precursors and products of differentially regulated genes due to prodigiosin. Therefore, the corroborated data suggests that prodigiosin majorly affects H. armigera development through dysregulation of the Juvenile hormone-dopamine system and can be considered as a bioactive scaffold to design insect-pest management compounds. This study provides the first report of in-depth analysis of insecticidal system dynamics in H. armigera insects upon prodigiosin feeding via gene expression and metabolic change via omics approach.

Design, synthesis and evaluation of novel pyrrole-hydroxybutenolide hybrids as promising antiplasmodial and anti-inflammatory agents

In the pursuance of novel scaffolds with promising antiplasmodial and anti-inflammatory activity, a series of twenty-one compounds embraced with most promising penta-substituted pyrrole and biodynamic hydroxybutenolide in single skeleton was designed and synthesized. These pyrrole-hydroxybutenolide hybrids were evaluated against Plasmodium falciparum parasite. Four hybrids 5b, 5d, 5t and 5u exhibited good activity with IC₅₀ of 0.60, 0.88, 0.97 and 0.96 μM for chloroquine sensitive (Pf3D7) strain and 3.92, 4.31, 4.21 and 1.67 μM for chloroquine resistant (PfK1) strain, respectively. In vivo efficacy of 5b, 5d, 5t and 5u was studied against the P. yoelii nigeriensis N67 (a chloroquine-resistant) parasite in Swiss mice at a dose of 100 mg/kg/day for 4 days via oral route. 5u was found to show maximum 100% parasite inhibition with considerably increased mean survival time. Simultaneously, the series of compounds was screened for anti-inflammatory potential. In preliminary assays, nine compounds showed more than 85% inhibition in hu-TNFα cytokine levels in LPS stimulated THP-1 monocytes and seven compounds showed more than 40% decrease in fold induction in reporter gene activity analyzed via Luciferase assay. 5p and 5t were found to be most promising amongst the series, thus were taken up for further in vivo studies. Wherein, mice pre-treated with them showed a dose dependent inhibition in carrageenan induced paw swelling. Moreover, the results of in vitro and in vivo pharmacokinetic parameters indicated that the synthesized pyrrole-hydroxybutenolide conjugates abide by the required criteria for the development of orally active drug and thus this scaffold can be used as pharmacologically active framework that should be considered for the development of potential antiplasmodial and anti-inflammatory agents.

Neuroprotective efficacy of the bacterial metabolite, prodigiosin, against aluminium chloride-induced neurochemical alternations associated with Alzheimer's disease murine model: Involvement of Nrf2/HO-1/NF-κB signaling

Prodigiosin (PDG) is a bacterial metabolite with numerous biological and pharmaceutical properties. Exposure to aluminium is considered a root etiological factor in the pathological progress of Alzheimer's disease (AD). Here, in this investigation, we explored the neuroprotective potential of PDG against aluminium chloride (AlCl₃ )-mediated AD-like neurological alterations in rats. For this purpose, rats were gavaged either AlCl₃ (100 mg/kg), PDG (300 mg/kg), or both for 42 days. As a result of the analyzes performed on the hippocampal tissue, it was observed that AlCl₃ induced biochemical, molecular, and histopathological changes like those related to AD. PDG pre-treatment significantly decreased acetylcholinesterase activity and restored the levels of brain-derived neurotrophic factor, monoamines (dopamine, norepinephrine, and serotonin), and transmembrane protein (Na⁺ /K⁺ -ATPase). Furthermore, PDG boosted the hippocampal antioxidant capacity, as shown by the increased superoxide dismutase, catalase, glutathione peroxidase, glutathione reductase, and glutathione contents. These findings were accompanied by decreases in malondialdehyde and nitric oxide levels. The antioxidant effect may promote the upregulation of the expression of antioxidant genes (Nrf2 and HO-1). Moreover, PDG exerted notable anti-inflammatory effects via the lessening of interleukin-1 beta, tumor necrosis factor-alpha, cyclooxygenase-2, nuclear factor kappa B, and decreases in the gene expression of inducible nitric oxide synthase. In addition, noteworthy decreases in pro-apoptotic (Bax and caspase-3) levels and increases in anti-apoptotic (Bcl-2) biomarkers suggested an anti-apoptotic effect of PDG. In support, the hippocampal histological examination validated the aforementioned changes. To summarize, the promising neuromodulatory, antioxidative, anti-inflammatory, and anti-apoptotic activities of PDG establish it as a potent therapeutic option for AD.

Therapeutic antischizophrenic activity of prodigiosin and selenium co-supplementation against amphetamine hydrochloride-induced behavioural changes and oxidative, inflammatory, and apoptotic challenges in rats

Schizophrenia (SCZ), a multifactorial neuropsychiatric disorder, is treated with inefficient antipsychotics and linked to poor treatment outcomes. This study, therefore, investigated the combined administration of prodigiosin (PDG) and selenium (Na₂SeO₃) against SCZ induced by amphetamine (AMPH) in rats. Animals were allocated into four groups corresponding to their respective 7-day treatments: control, AMPH (2 mg/kg), PDG (300 mg/kg) + Na₂SeO₃ (2 mg/kg), and AMPH + PDG + Na₂SeO₃. The model group exhibited biochemical, molecular, and histopathological changes similar to those of the SCZ group. Contrastingly, co-administration of PDG and Na₂SeO₃ significantly increased the time for social interaction and decreased AChE and dopamine. It also downregulated the gene expression of NMDAR1 and restored neurotrophin (BDNF and NGF) levels. Further, PDG combined with Na₂SeO₃ improved the antioxidant defence of the hippocampus by boosting the activities of SOD, CAT, GPx, and GR. These findings were accompanied by an increased GSH, alongside decreased MDA and NO levels. Furthermore, schizophrenic rats having received PDG and Na₂SeO₃ displayed markedly lower IL-1β and TNF-α levels compared to the model group. Interestingly, remarkable declines in the Bax (pro-apoptotic) and increases in Bcl-2 (anti-apoptotic) levels were observed in the SCZ group that received PDG and Na₂SeO₃. The hippocampal histological examination confirmed these changes. Collectively, these findings show that the co-administration of PDG and Na₂SeO₃ may have a promising therapeutic effect for SCZ. This is mediated by mechanisms related to the modulation of cholinergic, dopaminergic, and glutaric neurotransmission and neurotrophic factors, alongside the suppression of oxidative damage, neuroinflammation, and apoptosis machinery.

Evaluation of the antineoplastic property of prodigiosins and 5-fluorouracil in restraining the growth of Ehrlich solid tumors in mice

Prodigiosins have been shown to have anticancer activities. 5-Fluorouracil (5-FU) is broadly used chemotherapeutic drug that treats different solid tumors including breast cancer but has low response rates and a variety of side effects. In this study, we evaluated the anticancer properties of prodigiosins in a murine model "Ehrlich tumor" and tested whether it can be added to 5-FU to potentiate its effects. Markers of oxidative stress; MDA, NO, and GSH levels were evaluated as well as antioxidant enzyme activities of CAT SOD, GR, and GPx. The levels of Bax, Bcl-2, PCNA, and NF-κB proteins were measured using ELISA kits. The mRNAs of p53 and Cdc2 and Casp3 were quantitatively measured by real-time PCR and ELISA respectively. Cell cycle analysis was performed using flow cytometery. Prodigiosins did not influence tumor volume. Prodigiosins have not induced oxidative stress while 5-FU did increase MDA, NO but decreased GSH levels. The combination prodigiosins and 5-FU did reduce oxidative stress markers; MDA, NO and increased GSH levels. Prodigiosins significantly increased CAT only while 5-FU did decreased SOD, CAT, GPx, and GR. The combination prodigiosins and 5-FU increased the levels of these enzymes again. Prodigiosins increased the Bax/Bcl-2 ratio while the combination deceased it. In conclusion, prodigiosins have pronounced anticancer properties but their combination with 5-FU decreased oxidative stress exerted by 5-FU but weakened the apoptotic effects of 5-FU. Prodigiosins could affect a key mechanism through which 5-FU exerts its tumor inhibitory effects.

Prediction of Antileishmanial Compounds: General Model, Preparation, and Evaluation of 2-Acylpyrrole Derivatives

In this work, the SOFT.PTML tool has been used to pre-process a ChEMBL dataset of pre-clinical assays of antileishmanial compound candidates. A comparative study of different ML algorithms, such as logistic regression (LOGR), support vector machine (SVM), and random forests (RF), has shown that the IFPTML-LOGR model presents excellent values of specificity and sensitivity (81-98%) in training and validation series. The use of this software has been illustrated with a practical case study focused on a series of 28 derivatives of 2-acylpyrroles 5a,b, obtained through a Pd(II)-catalyzed C-H radical acylation of pyrroles. Their in vitro leishmanicidal activity against visceral (L. donovani) and cutaneous (L. amazonensis) leishmaniasis was evaluated finding that compounds 5bc (IC₅₀ = 30.87 μM, SI > 10.17) and 5bd (IC₅₀ = 16.87 μM, SI > 10.67) were approximately 6-fold more selective than the drug of reference (miltefosine) in in vitro assays against L. amazonensis promastigotes. In addition, most of the compounds showed low cytotoxicity, CC₅₀ > 100 μg/mL in J774 cells. Interestingly, the IFPMTL-LOGR model predicts correctly the relative biological activity of these series of acylpyrroles. A computational high-throughput screening (cHTS) study of 2-acylpyrroles 5a,b has been performed calculating >20,700 activity scores vs a large space of 647 assays involving multiple Leishmania species, cell lines, and potential target proteins. Overall, the study demonstrates that the SOFT.PTML all-in-one strategy is useful to obtain IFPTML models in a friendly interface making the work easier and faster than before. The present work also points to 2-acylpyrroles as new lead compounds worthy of further optimization as antileishmanial hits.

Recent Advances in Prodigiosin as a Bioactive Compound in Nanocomposite Applications

Bionanocomposites based on natural bioactive entities have gained importance due to their abundance; renewable and environmentally benign nature; and outstanding properties with applied perspective. Additionally, their formulation with biological molecules with antimicrobial, antioxidant, and anticancer activities has been produced nowadays. The present review details the state of the art and the importance of this pyrrolic compound produced by microorganisms, with interest towards Serratia marcescens, including production strategies at a laboratory level and scale-up to bioreactors. Promising results of its biological activity have been reported to date, and the advances and applications in bionanocomposites are the most recent strategy to potentiate and to obtain new carriers for the transport and controlled release of prodigiosin. Prodigiosin, a bioactive secondary metabolite, produced by Serratia marcescens, is an effective proapoptotic agent against bacterial and fungal strains as well as cancer cell lines. Furthermore, this molecule presents antioxidant activity, which makes it ideal for treating wounds and promoting the general improvement of the immune system. Likewise, some of the characteristics of prodigiosin, such as hydrophobicity, limit its use for medical and biotechnological applications; however, this can be overcome by using it as a component of a bionanocomposite. This review focuses on the chemistry and the structure of the bionanocomposites currently developed using biorenewable resources. Moreover, the work illuminates recent developments in pyrrole-based bionanocomposites, with special insight to its application in the medical area.

Downstream Process Development for Extraction of Prodigiosin: Statistical Optimization, Kinetics, and Biochemical Characterization

Prodigiosin is natural red colourant derived from Serratia marcescens. However, the high cost of prodigiosin restricts its use in food and pharmaceutical industries, which can be addressed with the design of a suitable extraction procedure. Therefore, the present study aims to use Taguchi methodology to optimize various process parameters during ultrasound-assisted extraction (UAE) to get a higher prodigiosin extraction yield. The most significant contribution comes from the solid-to-liquid ratio (36.66%), followed by sonication of duty cycle (34.82%), medium pH (15.7%), and acoustic intensity (12.82%). The Taguchi technique predicts the highest optimal yield using the solid-liquid ratio (0.3 g/mL), duty cycle sonication (75%), acoustic intensity (12.5 w/cm²), and medium pH (3) as parameters. When the extraction conditions were optimized, the yield of prodigiosin increased by 4166.89 mg/L. In the future, the above extraction conditions determined using Taguchi approach will be applied for large-scale extraction of prodigiosin. Finally, a second-order kinetic model is used to suit the batch extraction investigation and the second-order rate constant (k) has a value of 4 × 10^-5 L/mg/min. In the future, the rate constant, which is reported for the first time, will be used to create a batch extractor for commercial extraction of prodigiosin. Prodigiosin has also been shown to have substantial antioxidant and scavenging properties, which increase in a dose-dependent way with prodigiosin concentration. Because of its antioxidant and scavenging properties, prodigiosin can be used as food additives or pharmaceutical ingredients in industries.

The combined effects of nanoplastics and dibutyl phthalate on Streptomyces coelicolor M145

The environmental and human health risks posed by nanoplastics have attracted considerable attention; however, research on the combined toxicity of nanoplastics and plasticizers is limited. This study analyzed the combined effects of nanoplastics and dibutyl phthalate (DBP) on Streptomyces coelicolor M145 (herein referred to as M145) and its mechanism. The results demonstrated that when the concentration of both nanoplastics and DBP was 1 mg/L, the co-addition was not toxic to M145. When the DBP concentration increased to 5 mg/L, the combined toxicity of 1 mg/L nanoplastics and 5 mg/L DBP reduced when compared to the 5 mg/L DBP treatment group. Similarly, the combined toxicity of 10 mg/L nanoplastics and 1 mg/L DBP on M145 was also lower than that of only 10 mg/L nanoplastics. The co-addition of 10 mg/L nanoplastics and 5 mg/L DBP resulted in the lowest survival rate (41.3%). The key reason for differences in cytotoxicity were variations in the agglomeration of nanoplastics and the adsorption of DBP on nanoplastics. The combination of 10 mg/L nanoplastics and 5 mg/L DBP maximized the production of antibiotics; actinorhodin and undecylprodigiosin yields were 3.5 and 1.8-fold higher than that of the control, respectively. This indicates that the excessive production of antibiotics may be a protective mechanism for bacteria. This study provides a new perspective for assessing the risk of co-exposure to nanoplastics and organic contaminants on microorganisms in nature.

Synthesis, Anticancer Potential and Comprehensive Toxicity Studies of Novel Brominated Derivatives of Bacterial Biopigment Prodigiosin from Serratia marcescens ATCC 27117

Prodigiosins (prodiginines) are a class of bacterial secondary metabolites with remarkable biological activities and color. In this study, optimized production, purification, and characterization of prodigiosin (PG) from easily accessible Serratia marcescens ATCC 27117 strain has been achieved to levels of 14 mg/L of culture within 24 h. Furthermore, environmentally friendly bromination of produced PG was used to afford both novel mono- and dibrominated derivatives of PG. PG and its Br derivatives showed anticancer potential with IC₅₀ values range 0.62–17.00 µg/mL for all tested cancer cell lines and induction of apoptosis but low selectivity against healthy cell lines. All compounds did not affect Caenorhabditiselegans at concentrations up to 50 µg/mL. However, an improved toxicity profile of Br derivatives in comparison to parent PG was observed in vivo using zebrafish (Danio rerio) model system, when 10 µg/mL applied at 6 h post fertilization caused death rate of 100%, 30% and 0% by PG, PG-Br, and PG-Br_2, respectively, which is a significant finding for further structural optimizations of bacterial prodigiosins. The drug-likeness of PG and its Br derivatives was examined, and the novel Br derivatives obey the Lipinski’s “rule of five”, with an exemption of being more lipophilic than PG, which still makes them good targets for further structural optimization.

Prodigiosin: a promising biomolecule with many potential biomedical applications

Pigments are among the most fascinating molecules found in nature and used by human civilizations since the prehistoric ages. Although most of the bio-dyes reported in the literature were discovered around the eighties, the necessity to explore novel compounds for new biological applications has made them resurface as potential alternatives. Prodigiosin (PG) is an alkaloid red bio-dye produced by diverse microorganisms and composed of a linear tripyrrole chemical structure. PG emerges as a really interesting tool since it shows a wide spectrum of biological activities, such as antibacterial, antifungal, algicidal, anti-Chagas, anti-amoebic, antimalarial, anticancer, antiparasitic, antiviral, and/or immunosuppressive. However, PG vehiculation into different delivery systems has been proposed since possesses low bioavailability because of its high hydrophobic character (XLogP3-AA = 4.5). In the present review, the general aspects of the PG correlated with synthesis, production process, and biological activities are reported. Besides, some of the most relevant PG delivery systems described in the literature, as well as novel unexplored applications to potentiate its biological activity in biomedical applications, are proposed.

Optimized prodigiosin production with Pseudomonas putida KT2440 using parallelized non-invasive online monitoring

The red pigment prodigiosin is of high pharmaceutical interest, due to its potential applications as an antitumor drug and antibiotic agent. As previously demonstrated, Pseudomonas putida KT2440 is a suitable host for prodigiosin production, as it exhibits high tolerance towards the antimicrobial properties of prodigiosin. So far, prodigiosin concentrations of up to 94 mg/L have been achieved in shake flask cultivations. For the characterization and optimization of the prodigiosin production process, the scattered light of P. putida and fluorescence of prodigiosin was measured. The excitation and emission wavelengths for prodigiosin measurement were analyzed by recording 2D fluorescence spectra. The strongest prodigiosin fluorescence was obtained at a wavelength combination of 535/560 nm. By reducing the temperature to 18 °C and using 16 g/L glucose, the prodigiosin concentration was more than doubled compared to the initial cultivation conditions. The obtained results demonstrate the capabilities of parallelized microscale cultivations combined with non-invasive online monitoring of fluorescence for rapid bioprocess development, using prodigiosin as a molecule of current biotechnological interest.

Synthesis of N-Fused Dithia and Dibenzi Homoporphyrins

N-fused dithia and dibenzi homoporphyrins have been synthesized using [2+2] approach by condensing one equivalent of appropriate dithienyl/di p-phenylene ethene diol with one equivalent of N-confused dipyrromethane in CH2Cl2 under...

Investigating Alkylated Prodigiosenes and Their Cu(II)-Dependent Biological Activity: Interactions with DNA, Antimicrobial and Photoinduced Anticancer Activity

Prodigiosenes are a family of red pigments with versatile biological activity. Their tripyrrolic core structure has been modified many times in order to manipulate the spectrum of activity. We have been looking systematically at prodigiosenes substituted at the C ring with alkyl chains of different lengths, in order to assess the relevance of this substituent in a context that has not been investigated before for these derivatives: Cu(II) complexation, DNA binding, self‐activated DNA cleavage, photoinduced cytotoxicity and antimicrobial activity. Our results indicate that the hydrophobic substituent has a clear influence on the different aspects of their biological activity. The cytotoxicity study of the Cu(II) complexes of these prodigiosenes shows that they exhibit a strong cytotoxic effect towards the tested tumor cell lines. The Cu(II) complex of a prodigiosene lacking any alkyl chain excelled in its photoinduced anticancer activity, thus demonstrating the potential of prodigiosenes and their metal complexes for an application in photodynamic therapy (PDT). Two derivatives along with their Cu(II) complexes showed also antimicrobial activity against Staphylococcus aureus strains.

Enhanced Prodigiosin Production in Serratia marcescens JNB5-1 by Introduction of a Polynucleotide Fragment into the pigN 3' Untranslated Region and Disulfide Bonds into O-Methyl Transferase (PigF)

In Serratia marcescens JNB5-1, prodigiosin was highly produced at 30°C, but it was noticeably repressed at ≥37°C. Our initial results demonstrated that both the production and the stability of the O-methyl transferase (PigF) and oxidoreductase (PigN) involved in the prodigiosin pathway in S. marcescens JNB5-1 sharply decreased at ≥37°C. Therefore, in this study, we improved mRNA stability and protein production using de novo polynucleotide fragments (PNFs) and the introduction of disulfide bonds, respectively, and observed their effects on prodigiosin production. Our results demonstrate that adding PNFs at the 3' untranslated regions of pigF and pigN significantly improved the mRNA half-lives of these genes, leading to an increase in the transcript and expression levels. Subsequently, the introduction of disulfide bonds in pigF improved the thermal stability, pH stability, and copper ion resistance of PigF. Finally, shake flask fermentation showed that the prodigiosin titer with the engineered S. marcescens was increased by 61.38% from 5.36 to 8.65 g/liter compared to the JNB5-1 strain at 30°C and, significantly, the prodigiosin yield increased 2.05-fold from 0.38 to 0.78 g/liter at 37°C. In this study, we revealed that the introduction of PNFs and disulfide bonds greatly improved the expression and stability of pigF and pigN, hence efficiently enhancing prodigiosin production with S. marcescens at 30 and 37°C. IMPORTANCE This study highlights a promising strategy to improve mRNA/enzyme stability and to increase production using de novo PNF libraries and the introduction of disulfide bonds into the protein. PNFs could increase the half-life of target gene mRNA and effectively prevent its degradation. Moreover, PNFs could increase the relative intensity of target genes without affecting the expression of other genes; as a result, it could alleviate the cellular burden compared to other regulatory elements such as promoters. In addition, we obtained a PigF variant with improved activity and stability by the introduction of disulfide bonds into PigF. Collectively, we demonstrate here a novel approach for improving mRNA/enzyme stability using PNFs, which results in enhanced prodigiosin production in S. marcescens at 30°C.

Practical Enzymatic Production of Carbocycles

The Pd-catalyzed carbon-carbon bond formation pioneered by Heck in 1969 has dominated medicinal chemistry development for the ensuing fifty years. As the demand for more complex three-dimensional active pharmaceuticals continues to increase, preparative enzyme-mediated assembly, by virtue of its exquisite selectivity and sustainable nature, is poised to provide a practical and affordable alternative for accessing such compounds. In this minireview, we summarize recent state-of-the-art developments in practical enzyme-mediated assembly of carbocycles. When appropriate, background information on the enzymatic transformation is provided and challenges and/or limitations are also highlighted.

Prodigiosin inhibits bacterial growth and virulence factors as a potential physiological response to interspecies competition

Prodigiosin, a red linear tripyrrole pigment, has long been recognised for its antimicrobial property. However, the physiological contribution of prodigiosin to the survival of its producing hosts still remains undefined. Hence, the aim of this study was to investigate the biological role of prodigiosin from Serratia marcescens, particularly in microbial competition through its antimicrobial activity, towards the growth and secreted virulence factors of four clinical pathogenic bacteria (methicillin-resistant Staphylococcus aureus (MRSA), Enterococcus faecalis, Salmonella enterica serovar Typhimurium and Pseudomonas aeruginosa) as well as Staphylococcus aureus and Escherichia coli. Prodigiosin was first extracted from S. marcescens and its purity confirmed by absorption spectrum, high performance liquid chromatography (HPLC) and liquid chromatography-tandem mass spectrophotometry (LC-MS/MS). The extracted prodigiosin was antagonistic towards all the tested bacteria. A disc-diffusion assay showed that prodigiosin is more selective towards Gram-positive bacteria and inhibited the growth of MRSA, S. aureus and E. faecalis and Gram-negative E. coli. A minimum inhibitory concentration of 10 μg/μL of prodigiosin was required to inhibit the growth of S. aureus, E. coli and E. faecalis whereas > 10 μg/μL was required to inhibit MRSA growth. We further assessed the effect of prodigiosin towards bacterial virulence factors such as haemolysin and production of protease as well as on biofilm formation. Prodigiosin did not inhibit haemolysis activity of clinically associated bacteria but was able to reduce protease activity for MRSA, E. coli and E. faecalis as well as decrease E. faecalis, Salmonella Typhimurium and E. coli biofilm formation. Results of this study show that in addition to its role in inhibiting bacterial growth, prodigiosin also inhibits the bacterial virulence factor protease production and biofilm formation, two strategies employed by bacteria in response to microbial competition. As clinical pathogens were more resistant to prodigiosin, we propose that prodigiosin is physiologically important for S. marcescens to compete against other bacteria in its natural soil and surface water environments.

Total Synthesis and Antimalarial Activity of 2-(p-Hydroxybenzyl)-prodigiosins, Isoheptylprodigiosin, and Geometric Isomers of Tambjamine MYP1 Isolated from Marine Bacteria

Highly efficient and straightforward synthetic routes toward the first total synthesis of 2-(p-hydroxybenzyl)-prodigiosins (2-5), isoheptylprodigiosin (6), and geometric isomers of tambjamine MYP1 ((E/Z)-7) have been developed. The crucial steps involved in these synthetic routes are the construction of methoxy-bipyrrole-carboxaldehydes (MBCs) and a 20-membered macrocyclic core and a regioselective demethylation of MBC analogues. These new synthetic routes enabled us to generate several natural prodiginines 24-27 in larger quantity. All of the synthesized natural products exhibited potent asexual blood-stage antiplasmodial activity at low nanomolar concentrations against a panel of Plasmodium falciparum parasites, with a great therapeutic index. Notably, prodiginines 6 and 24-27 provided curative in vivo efficacy against erythrocytic Plasmodium yoelii at 25 mg/kg × 4 days via oral route in a murine model. No overt clinical toxicity or behavioral change was observed in any mice treated with prodiginines and tambjamines.

High-level production of microbial prodigiosin: A review

Prodigiosin is a natural red pigment derived primarily from secondary metabolites of microorganisms, especially Serratia marcescens. It can also be chemically synthesized. Prodigiosin has been proven to have antitumor, antibacterial, antimalaria, anti-insect, antialgae, and immunosuppressive activities, and is gaining increasing important in the global market because of its great potential application value in clinical medicine development, environmental treatment, preparation of food additives, and so on. Due to the low efficiency of prodigiosin chemical synthesis, high-level prodigiosin of production by microorganisms are necessary for prodigiosin applications. In this paper, the production of prodigiosin by microorganism in recent decades is reviewed. The methods and strategies for increasing the yield of prodigiosin are discussed from the aspects of medium composition, additives, factors affecting production conditions, strain modification, and fermentation methods.

Bacterial natural products in the fight against mosquito-transmitted tropical diseases

Covering: up to 2019 Secondary metabolites of microbial origin have long been acknowledged as medically relevant, but their full potential remains largely unexploited. Of the countless natural compounds discovered thus far, only 5-10% have been isolated from microorganisms. At the same time, while whole-genome sequencing has demonstrated that bacteria and fungi often encode natural products, only a few genera have yet been mined for new compounds. This review explores the contributions of bacterial natural products to combatting infection by malaria parasites, filarial worms, and arboviruses such as dengue, Zika, Chikungunya, and West Nile. It highlights how molecules isolated from microorganisms ranging from marine cyanobacteria to mosquito endosymbionts can be exploited as antimicrobials and antivirals. Pursuit of this mostly untapped source of chemical entities will potentially result in new interventions against these tropical diseases, which are urgently needed to combat the increase in the incidence of resistance.

Biotechnological Activities and Applications of Bacterial Pigments Violacein and Prodigiosin

In this review, we discuss violacein and prodigiosin, two chromogenic bacterial secondary metabolites that have diverse biological activities. Although both compounds were "discovered" more than seven decades ago, interest into their biological applications has grown in the last two decades, particularly driven by their antimicrobial and anticancer properties. These topics will be discussed in the first half of this review. The latter half delves into the current efforts of groups to produce these two compounds. This includes in both their native bacterial hosts and heterogeneously in other bacterial hosts, including discussing some of the caveats related to the yields reported in the literature, and some of the synthetic biology techniques employed in this pursuit.

Stringent Starvation Protein Regulates Prodiginine Biosynthesis via Affecting Siderophore Production in Pseudoalteromonas sp. Strain R3

Prodiginines are a family of red-pigmented secondary metabolites with multiple biological activities. The biosynthesis of prodiginines is affected by various physiological and environmental factors. Thus, prodiginine biosynthesis regulation is highly complex and multifaceted. Although the regulatory mechanism for prodiginine biosynthesis has been extensively studied in Serratia and Streptomyces species, little is known about that in the marine betaproteobacterium Pseudoalteromonas In this study, we report that stringent starvation protein A (SspA), an RNA polymerase-associated regulatory protein, is required for the biosynthesis of prodiginine in Pseudoalteromonas sp. strain R3. The strain lacking sspA (ΔsspA) fails to produce prodiginine, which resulted from the downregulation of the prodiginine biosynthetic gene (pig) cluster. The effect of SspA on prodiginine biosynthesis is independent of histone-like nucleoid structuring protein (H-NS) and RpoS (σ^S). Further analysis demonstrates that the ΔsspA strain has a significant decrease in the transcription of the siderophore biosynthesis gene (pvd) cluster, leading to the inhibition of siderophore production and iron uptake. The ΔsspA strain regains the ability to synthesize prodiginine by cocultivation with siderophore producers or the addition of iron. Therefore, we conclude that SspA-regulated prodiginine biosynthesis is due to decreased siderophore levels and iron deficiency. We further show that the iron homeostasis master regulator Fur is also essential for pig transcription and prodiginine biosynthesis. Overall, our results suggest that SspA indirectly regulates the biosynthesis of prodiginine, which is mediated by the siderophore-dependent iron uptake pathway.IMPORTANCE The red-pigmented prodiginines are attracting increasing interest due to their broad biological activities. As with many secondary metabolites, the biosynthesis of prodiginines is regulated by both environmental and physiological factors. At present, studies on the regulation of prodiginine biosynthesis are mainly restricted to Serratia and Streptomyces species. This work focused on the regulatory mechanism of prodiginine biosynthesis in Pseudoalteromonas sp. R3. We found that stringent starvation protein A (SspA) positively regulates prodiginine biosynthesis via affecting the siderophore-dependent iron uptake pathway. The connections among SspA, iron homeostasis, and prodiginine biosynthesis were investigated. These findings uncover a novel regulatory mechanism for prodigiosin biosynthesis.

Concise Diastereoselective Total Synthesis of (±)-Parvistemonine A

We have developed a concise diastereoselective total synthesis of (±)-parvistemonine A. By using a Mukaiyama–Michael addition, an aza-Wittig reaction, a Paal–Knorr pyrrole synthesis, an acid-mediated annulation, and a Mitsunobu reaction as key steps, we achieved a total synthesis in which the longest linear sequence was ten steps and the overall yield was 19.6%. Additionally, the relative stereochemistry of parvistemonine A was confirmed by X-ray crystallographic analysis for the first time.

Production and Potential Applications of Bioconversion of Chitin and Protein-Containing Fishery Byproducts into Prodigiosin: A Review

The technology of microbial conversion provides a potential way to exploit compounds of biotechnological potential. The red pigment prodigiosin (PG) and other PG-like pigments from bacteria, majorly from Serratia marcescens, have been reported as bioactive secondary metabolites that can be used in the broad fields of agriculture, fine chemicals, and pharmacy. Increasing PG productivity by investigating the culture conditions especially the inexpensive carbon and nitrogen (C/N) sources has become an important factor for large-scale production. Investigations into the bioactivities and applications of PG and its related compounds have also been given increased attention. To save production cost, chitin and protein-containing fishery byproducts have recently been investigated as the sole C/N source for the production of PG and chitinolytic/proteolytic enzymes. This strategy provides an environmentally-friendly selection using inexpensive C/N sources to produce a high yield of PG together with chitinolytic and proteolytic enzymes by S. marcescens. The review article will provide effective references for production, bioactivity, and application of S. marcescens PG in various fields such as biocontrol agents and potential pharmaceutical drugs.

Synergistic toxic effects of ball-milled biochar and copper oxide nanoparticles on Streptomyces coelicolor M145

The toxic effects of multi-nanomaterial systems are receiving increasing attention owing to their inevitable release of various nanomaterials. Knowledge of the bioavailability of the new carbon material ball-milled biochar (BMB) and its synergistic toxicity with metal oxide nanoparticles in bacteria is currently limited. In this study, the interactions of BMB with copper oxide nanoparticles (CuO NPs) and their synergistic toxicity towards Streptomyces coelicolor M145 were analyzed. Results showed that the cytotoxicity, ROS level and permeability of cells changed greatly with the pyrolysis temperatures of biochar and the concentrations of CuO NPs. The greatest cytotoxicity (up to 63.1%) was achieved by adding 20 mg/L CuO NPs to BMB700. The ROS level and cell permeability of this treatment was also the highest, about 4.2 folds and 2.9 folds greater than that of control, respectively. The combination of 10 mg/L BMB700 with 10 mg/L CuO NPs can maximize production of antibiotics, with the yield of undecylprodigiosin (RED) and actinorhodin (ACT) 3.0 times and 4.2 times higher than that in the control, respectively, and the change trend of related genes was consistent with that of antibiotics production. Mechanism analysis showed that the different adsorption capacity of BMB of different pyrolysis temperatures on copper ions played a vital role in the synergistic toxicity, and the increase in cell membrane permeability caused by cell collisions with particles was also an important reason for cytotoxicity. Overall, the synergistic toxicity of BMB with other NPs varies the pyrolysis temperatures, when considering the synergistic toxicity of these materials, the preparation conditions need to be taken into account so as to assess their environmental risks more accurately. On the other hand, this research may provide a new approach for the antibiotic industry to increase its output.

Improved Prodigiosin Production by Relieving CpxR Temperature-Sensitive Inhibition

Prodigiosin (PG) is a typical secondary metabolite mainly produced by Serratia marcescens. CpxR protein is an OmpR family transcriptional regulator in Gram-negative bacteria. Firstly, it was found that insertion mutation of cpxR in S. marcescens JNB 5-1 by a transposon Tn5G increased the production of PG. Results from the electrophoretic mobility shift assay (EMSA) indicated that CpxR could bind to the promoter of the pig gene cluster and repress the transcription levels of genes involved in PG biosynthesis in S. marcescens JNB 5-1. In the ΔcpxR mutant strain, the transcription levels of the pig gene cluster and the genes involved in the pathways of PG precursors, such as proline, pyruvate, serine, methionine, and S-adenosyl methionine, were significantly increased, hence promoting the production of PG. Subsequently, a fusion segment composed of the genes proC, serC, and metH, responsible for proline, serine, and methionine, was inserted into the cpxR gene in S. marcescens JNB 5-1. On fermentation by the resultant engineered S. marcescens, the highest PG titer reached 5.83 g/L and increased by 41.9%, relative to the parental strain. In this study, we revealed the role of CpxR in PG biosynthesis and provided an alternative strategy for the engineering of S. marcescens to enhance PG production.

Identification of anisomycin, prodigiosin and obatoclax as compounds with broad-spectrum anti-parasitic activity

Parasitic infections are a major source of human suffering, mortality, and economic loss, but drug development for these diseases has been stymied by the significant expense involved in bringing a drug though clinical trials and to market. Identification of single compounds active against multiple parasitic pathogens could improve the economic incentives for drug development as well as simplifying treatment regimens. We recently performed a screen of repurposed compounds against the protozoan parasite Entamoeba histolytica, causative agent of amebic dysentery, and identified four compounds (anisomycin, prodigiosin, obatoclax and nithiamide) with low micromolar potency and drug-like properties. Here, we extend our investigation of these drugs. We assayed the speed of killing of E. histolytica trophozoites and found that all four have more rapid action than the current drug of choice, metronidazole. We further established a multi-institute collaboration to determine whether these compounds may have efficacy against other parasites and opportunistic pathogens. We found that anisomycin, prodigiosin and obatoclax all have broad-spectrum antiparasitic activity in vitro, including activity against schistosomes, T. brucei, and apicomplexan parasites. In several cases, the drugs were found to have significant improvements over existing drugs. For instance, both obatoclax and prodigiosin were more efficacious at inhibiting the juvenile form of Schistosoma than the current standard of care, praziquantel. Additionally, low micromolar potencies were observed against pathogenic free-living amebae (Naegleria fowleri, Balamuthia mandrillaris and Acanthamoeba castellanii), which cause CNS infection and for which there are currently no reliable treatments. These results, combined with the previous human use of three of these drugs (obatoclax, anisomycin and nithiamide), support the idea that these compounds could serve as the basis for the development of broad-spectrum anti-parasitic drugs.

Substrate Flexibility of the Flavin-Dependent Dihydropyrrole Oxidases PigB and HapB Involved in Antibiotic Prodigiosin Biosynthesis

In the biosynthesis of the tripyrrolic pigment prodigiosin, PigB is a predicted flavin-dependent oxidase responsible for the formation of 2-methyl-3-amylpyrrole (MAP) from a dihydropyrrole. To prove which dihydropyrrole is the true intermediate, both possibilities, 5-methyl-4-pentyl-3,4-dihydro-2H-pyrrole (5 a, resulting from transamination of the aldehyde of 3-acetyloctanal) and 2-methyl-3-pentyl-3,4-dihydro-2H-pyrrole (6, resulting from transamination of the ketone), were synthesised. Only 5 a restored pigment production in a strain of Serratia sp. ATCC 39006 blocked earlier in MAP biosynthesis. PigB is membrane-associated and inactive when its transmembrane domain was deleted, but HapB, its homologue in Hahella chejuensis, lacks the transmembrane domain and is active in solution. Two colourimetric assays for PigB and HapB were developed, and the HapB-catalysed reaction was kinetically characterised. Ten analogues of 5 a were synthesised, varying in the C2 and C3 side chains, and tested as substrates of HapB in vitro and for restoration of pigment production in Serratia ΔpigD in vivo. All lengths of side chain tested at C3 were accepted, but only short side chains at C2 were accepted. The knowledge that 5 a is an intermediate in prodigiosin biosynthesis and the ease of synthesis of analogues of 5 a makes a range of prodigiosin analogues readily available by mutasynthesis.

RedH and PigC Catalyze the Biosynthesis of Hybrubins via Phosphorylation of 4'-Methoxy-2,2'-Bipyrrole-5'-Carbaldehyde

Hybrubins are "unnatural" alkaloids with the same 4'-methoxy-2,2'-bipyrrole-5'-methine moiety found in prodiginines and a different ring derived from tetramic acids. Here, we demonstrated that RedH, a homologue of prodigiosin synthetase PigC, was responsible for the biosynthesis of hybrubins A and B in Streptomyces lividans In vitro reactions indicated that RedH and PigC catalyzed the intermolecular condensation between 4'-methoxy-2,2'-bipyrrole-5'-carbaldehyde (MBC) and (Z)-5-ethylidenetetramic acid (ETA) to produce hybrubin B. Moreover, we demonstrated that RedH and PigC activated MBC via phosphorylation of the aldehyde group to form an intermediate P_i-MBC and that the subsequent condensation between P_i-MBC and (Z)-5-ethylidenetetramic acid occurs in a nonenzymatic way.IMPORTANCE Hybrubins are an emerging class of prodiginines possessing a new C ring derived from 5'-substituted tetramic acids and the methylene bridge connecting the C ring at a different position. We have supposed that condensation between 4'-methoxy-2,2'-bipyrrole-5'-carbaldehyde (MBC) and 5-ethylidenetetramic acid (ETA) yields the hybrid natural products hybrubins, which was proposed to be catalyzed by the undecylprodigiosin synthetase RedH. However, it is doubted whether RedH is able to catalyze another type of condensation between MBC and tetramic acids. In this study, we have demonstrated that the MBC-ETA condensation proceeds through RedH/PigC-catalyzed enzymatic activation of MBC via phosphorylation and a nonenzymatic condensation of P_i-MBC with ETA. Since MBC analogues have been shown to be accepted by PigC, more hybrubin analogues might be produced by using combinations of MBC analogues and other tetramic acids in future studies.

A colourimetric high-throughput screening system for directed evolution of prodigiosin ligase PigC

A colourimetric high-throughput screening system was developed for the first directed evolution campaign on PigC towards production of artificial prodiginines.

Novel Prodiginine Derivatives Demonstrate Bioactivities on Plants, Nematodes, and Fungi

Bacterial metabolites represent an invaluable source of bioactive molecules which can be used as such or serve as chemical frameworks for developing new antimicrobial compounds for various applications including crop protection against pathogens. Prodiginines are tripyrrolic, red-colored compounds produced by many bacterial species. Recently, due to the use of chemical-, bio-, or mutasynthesis, a novel group of prodiginines was generated. In our study, we perform different assays to evaluate the effects of prodigiosin and five derivatives on nematodes and plant pathogenic fungi as well as on plant development. Our results showed that prodigiosin and the derivatives were active against the bacterial feeding nematode Caenorhabditis elegans in a concentration- and derivative-dependent manner while a direct effect on infective juveniles of the plant parasitic nematode Heterodera schachtii was observed for prodigiosin only. All compounds were found to be active against the plant pathogenic fungi Phoma lingam and Sclerotinia sclerotiorum. Efficacy varied depending on compound concentration and chemical structure. We observed that prodigiosin (1), the 12 ring- 9, and hexenol 10 derivatives are neutral or even positive for growth of Arabidopsis thaliana depending on the applied compound concentration, whereas other derivatives appear to be suppressive. Our infection assays revealed that the total number of developed H. schachtii individuals on A. thaliana was decreased to 50% in the presence of compounds 1 or 9. Furthermore, female nematodes and their associated syncytia were smaller in size. Prodiginines seem to indirectly inhibit H. schachtii parasitism of the plant. Further research is needed to elucidate their mode of action. Our results indicate that prodiginines are promising metabolites that have the potential to be developed into novel antinematodal and antifungal agents.

A comparative analysis of ball-milled biochar, graphene oxide, and multi-walled carbon nanotubes with respect to toxicity induction in Streptomyces

Ball-milled biochar has recently attracted a lot of attention due to the simplicity of its preparation and low cost. However, it is unknown if the biochar is environmentally safe. Here, the toxic effect of ball-milled biochar on Streptomyces was compared to that of pristine biochar and two other carbon nanomaterials of different shapes-graphene oxide and multi-walled carbon nanotubes. The effect of these different materials on antibiotic production was characterized. The results showed that even at concentrations of up to 10 mg/L, pristine biochar had a negligible effect on toxicity and antibiotic production in Streptomyces. However, after ball milling, the physical and chemical properties of biochar changed dramatically. Cells were severely damaged, and there was a significant increase in antibiotic production after the addition of ball-milled biochar. Exposure to 10 mg/L of ball-milled biochar caused massive cell disruption; the survival rate of Streptomyces coelicolor M145 cells was only 68.2% as compared to 90% after treatment with 10 mg/L graphene oxide and multi-walled carbon nanotubes. The secretion of the antibiotics- the red intracellular pigment undecylprodigiosin (RED) and blue diffusible pigment actinorhodin (ACT) was enhanced with the highest level in treatment with ball milled biochar, as compared to that with the other two carbon nanomaterials. This effect can be attributed to increased expression of pathway-specific regulatory genes redD, redZ and actⅡ-ORF4. Ball-milled biochar can be developed as an effective additive to increase antibiotic yield. However, we should restrict the large-scale use of ball-milled biochar before fully understanding its impact on the environment and human health.

Prodigiosin Promotes Nrf2 Activation to Inhibit Oxidative Stress Induced by Microcystin-LR in HepG2 Cells

Microcystin-LR (MC-LR), a cyanotoxin produced by cyanobacteria, induces oxidative stress in various types of cells. Prodigiosin, a red linear tripyrrole pigment, has been recently reported to have antimicrobial, antioxidative, and anticancer properties. How prodigiosin reacts to reactive oxygen species (ROS) induced by MC-LR is still undetermined. This study aimed to examine the effect of prodigiosin against oxidative stress induced by MC-LR in HepG2 cells. Ros was generated after cells were treated with MC-LR and was significantly inhibited with treatment of prodigiosin. In prodigiosin-treated cells, the levels of nuclear factor erythroid 2-related factor 2 (Nrf2) and Nrf2-related phase II enzyme heme oxygenase-1 (HO-1) were increased. Besides, prodigiosin contributed to enhance nuclear Nrf2 level and repressed ubiquitination. Furthermore, prodigiosin promoted Nrf2 protein level and inhibited ROS in Nrf2 knocked down HepG2 cells. Results indicated that prodigiosin reduced ROS induced by MC-LR by enhancing Nrf2 translocation into the nucleus in HepG2 cells. The finding presents new clues for the potential clinical applications of prodigiosin for inhibiting MC-LR-induced oxidative injury in the future.

Al2O3 nanoparticles promote secretion of antibiotics in Streptomyces coelicolor by regulating gene expression through the nano effect

Toxic effects of nanoparticles (NPs) on microorganisms have attracted substantial attention; however, there are few reports on whether NPs can affect the secondary metabolism of microbes. To investigate the toxic effects of Al₂O₃ NPs on cell growth and antibiotic secretion, Streptomyces coelicolor M145 was exposed to Al₂O₃ NPs with diameters of 30 and 80 nm and bulk Al₂O₃ at concentrations up to 1000 mg/L. The results indicated that differences in the toxicity of Al₂O₃ NPs were related to the particle size. In treatment with Al₂O₃ NPs, the maximum yields of undecylprodigiosin (RED) and actinorhodin (ACT) were 3.7- and 4.6-fold greater than that of the control, respectively, and the initial time of antibiotic production was much shorter. ROS quenching experiment by N-acetylcysteine (NAC) confirmed that ROS were responsible for the increased RED production. From 0 to 72 h, ROS had a significant impact on ACT production; however, after 72 h, the ROS content began to decrease until it disappeared. During ongoing exposure (0-144 h), ACT production continued to increase, indicating that in addition to ROS, nano effect of Al₂O₃ NPs also played roles in this process. Transcriptional analysis demonstrated that Al₂O₃ NPs could increase the expression levels of antibiotic biosynthetic genes and two-component systems (TCSs) and inhibit the expression levels of primary metabolic pathways. This study provides a new perspective for understanding the mechanisms of antibiotic production in nature and reveals important implications for exploring other uses of NPs in biomedical applications or regulation of antibiotics in nature.

Actinobacteria-a promising natural source of anti-biofilm agents

A biofilm is a community of microorganisms attached to a surface and embedded in a matrix of extracellular polymeric substances. Biofilms confer resistance towards conventional antibiotic treatments; thus, there is an urgent need for newer and more effective antimicrobial agents that can act against these biofilms. Due to this situation, various studies have been done to investigate the anti-biofilm effects of natural products including bioactive compounds extracted from microorganisms such as Actinobacteria. This review provides an insight into the anti-biofilm potential of Actinobacteria against various pathogenic bacteria, which hopefully provides useful information, guidance, and improvements for future antimicrobial studies. Nevertheless, further research on the anti-biofilm mechanisms and compound modifications to produce more potent anti-biofilm effects are required.

Insights into the anti-infective properties of prodiginines

Prodiginines are a large family of tripyrrole alkaloids that contain natural members produced by various bacteria and non-natural members obtained from chemical synthesis, enzymatic synthesis, and mutasynthesis. These compounds have attracted a great deal of attention due to their wide range of fascinating properties including anti-infective, anticancer, and immunosuppressive activities. In consideration of the great need for novel and effective anti-infective agents, this review is mainly focused on the current status of research on the anti-infective properties of prodiginines, highlighting their antibacterial, antifungal, antiprotozoal, anti-larval, and antiviral activities. Additionally, the multiple mechanisms by which prodiginines exert their anti-infective effects will also be discussed.