Re-wiring the regulation of the formicamycin biosynthetic gene cluster to enable the development of promising antibacterial compounds

Total Synthesis of the Phenylnaphthacenoid Type II Polyketide Antibiotic Formicamycin H via Regioselective Ruthenium-Catalyzed Hydrogen Auto-Transfer [4 + 2] Cycloaddition

The first total synthesis of the pentacyclic phenylnaphthacenoid type II polyketide antibiotic formicamycin H is described. A key feature of the synthesis involves the convergent, regioselective assembly of the tetracyclic core via ruthenium-catalyzed α-ketol-benzocyclobutenone [4 + 2] cycloaddition. Double dehydration of the diol-containing cycloadduct provides an achiral enone, which upon asymmetric nucleophilic epoxidation and further manipulations delivers the penultimate tetracyclic trichloride in enantiomerically enriched form. Subsequent chemo- and atroposelective Suzuki cross-coupling of the tetracyclic trichloride introduces the E-ring to complete the total synthesis. Single-crystal X-ray diffraction analyses of two model compounds suggest that the initially assigned stereochemistry of the axially chiral C6-C7 linkage may require revision.

Diversity and potential functional role of phyllosphere-associated actinomycetota isolated from cupuassu (Theobroma grandiflorum) leaves: implications for ecosystem dynamics and plant defense strategies

Exploring the intricate relationships between plants and their resident microorganisms is crucial not only for developing new methods to improve disease resistance and crop yields but also for understanding their co-evolutionary dynamics. Our research delves into the role of the phyllosphere-associated microbiome, especially Actinomycetota species, in enhancing pathogen resistance in Theobroma grandiflorum, or cupuassu, an agriculturally valuable Amazonian fruit tree vulnerable to witches' broom disease caused by Moniliophthora perniciosa. While breeding resistant cupuassu genotypes is a possible solution, the capacity of the Actinomycetota phylum to produce beneficial metabolites offers an alternative approach yet to be explored in this context. Utilizing advanced long-read sequencing and metagenomic analysis, we examined Actinomycetota from the phyllosphere of a disease-resistant cupuassu genotype, identifying 11 Metagenome-Assembled Genomes across eight genera. Our comparative genomic analysis uncovered 54 Biosynthetic Gene Clusters related to antitumor, antimicrobial, and plant growth-promoting activities, alongside cutinases and type VII secretion system-associated genes. These results indicate the potential of phyllosphere-associated Actinomycetota in cupuassu for inducing resistance or antagonism against pathogens. By integrating our genomic discoveries with the existing knowledge of cupuassu's defense mechanisms, we developed a model hypothesizing the synergistic or antagonistic interactions between plant and identified Actinomycetota during plant-pathogen interactions. This model offers a framework for understanding the intricate dynamics of microbial influence on plant health. In conclusion, this study underscores the significance of the phyllosphere microbiome, particularly Actinomycetota, in the broader context of harnessing microbial interactions for plant health. These findings offer valuable insights for enhancing agricultural productivity and sustainability.

From antibiotic to antiviral: computational screening reveals a multi-targeting antibiotic from Streptomyces spp. against Nipah virus fusion proteins

Nipah Virus is a re-emerging zoonotic paramyxovirus that poses a significant threat to both swine industry and human health. The pursuit of potential antiviral agents with both preventive and therapeutic properties holds promise for targeting such viruses. To expedite this search, leveraging computational biology is essential. Streptomyces is renowned for its capacity to produce large and diverse metabolites with promising bioactivities. In the current study, we conducted a comprehensive structure-based virtual screening of 6524 Streptomyces spp. metabolites sourced from the StreptomeDB database to evaluate their potential inhibitory effects on three Nipah virus fusion (NiVF) protein conformations: NiVF pre-fusion 1-mer (NiVF-1mer), pre-fusion 3-mer (NiVF-3mer), and NiVF post-fusion (NiVF-PoF). Prior to virtual screening, the drug-likeness of Streptomyces spp. compounds was profiled using ADMET properties. From the 913 ADMET-filtered compounds, the subsequent targeted and confirmatory blind docking analysis revealed that S896 or virginiamycin M1, a known macrolide antibiotic, showed a maximum binding affinity with the NiVF proteins, suggesting a multi-targeting inhibitory property. In addition, the 200-ns molecular dynamics simulation and MM/PBSA analyses revealed stable and strong binding affinity between the NiVF-S896 complexes, indicating favorable interactions between S896 and the target proteins. These findings suggest the potential of virginiamycin M1, an antibiotic, as a promising multi-targeting antiviral drug. However, in vitro and in vivo experimental validations are necessary to assess their safety and efficacy.

Accraspiroketides A-B, Phenylnaphthacenoid-Derived Polyketides with Unprecedented [6 + 6+6 + 6] + [5 + 5] Spiro-Architecture

Two novel polyketides, accraspiroketides A (1) and B (2), which feature unprecedented [6 + 6+6 + 6] + [5 + 5] spiro chemical architectures, were isolated from Streptomyces sp. MA37 ΔaccJ mutant strain. Compounds 1-2 exhibit excellent activity against Gram-positive bacteria (MIC = 1.5-6.3 μg/mL). Notably, 1 and 2 have superior activity against clinically isolated Enterococcus faecium K60-39 (MIC = 4.0 μg/mL and 4.7 μg/mL, respectively) than ampicillin (MIC = 25 μg/mL).

Actinomycetes Associated with Arthropods as a Source of New Bioactive Compounds

Antimicrobial resistance is one of the main global threats to human health in the 21st century due to the rapid appearance of bacterial resistance and the lack of novel bioactive compounds. Natural products, especially from Actinomycetes, remain the best source to refill the drug industry pipeline. Different strategies have been pursued to increase the chances of discovering new molecules, such as studying underexplored environments like arthropod symbionts, which represent a relevant reservoir for active metabolites. This review summarizes recent research on the identification of bioactive molecules produced by Actinomycetes associated with arthropods' microbiome. The metabolites have been categorized based on their structural properties and host, highlighting that multidisciplinary approaches will be the key to fully understanding this complex relationship.

An unusual aromatase/cyclase programs the formation of the phenyldimethylanthrone framework in anthrabenzoxocinones and fasamycin

Aromatic polyketides are renowned for their wide-ranging pharmaceutical activities. Their structural diversity is mainly produced via modification of limited types of basic frameworks. In this study, we characterized the biosynthesis of a unique basic aromatic framework, phenyldimethylanthrone (PDA) found in (+)/(-)-anthrabenzoxocinones (ABXs) and fasamycin (FAS). Its biosynthesis employs a methyltransferase (Abx(+)M/Abx(-)M/FasT) and an unusual TcmI-like aromatase/cyclase (ARO/CYC, Abx(+)D/Abx(-)D/FasL) as well as a nonessential helper ARO/CYC (Abx(+)C/Abx(-)C/FasD) to catalyze the aromatization/cyclization of polyketide chain, leading to the formation of all four aromatic rings of the PDA framework, including the C9 to C14 ring and a rare angular benzene ring. Biochemical and structural analysis of Abx(+)D reveals a unique loop region, giving rise to its distinct acyl carrier protein-dependent specificity compared to other conventional TcmI-type ARO/CYCs, all of which impose on free molecules. Mutagenic analysis discloses critical residues of Abx(+)D for its catalytic activity and indicates that the size and shape of its interior pocket determine the orientation of aromatization/cyclization. This study unveils the tetracyclic and non-TcmN type C9 to C14 ARO/CYC, significantly expanding our cognition of ARO/CYCs and the biosynthesis of aromatic polyketide framework.

Unveiling nature's treasures: actinobacteria from Meghalaya's mining sites as sources of bioactive compounds

Coal and sillimanite mining sites present unique ecological niches favoring the growth of actinobacteria, a group of Gram-positive bacteria known for producing a wide array of bioactive compounds. Isolating these bacteria from such environments could unveil novel compounds with potential biotechnological applications. This study involved the isolation of actinobacteria from two mining sites in Meghalaya, India. The dominant genera from both sites were Streptomyces, Amycolatopsis, Nocardia, and Streptosporangium. Metabolic pathway prediction from 16S rRNA gene revealed several pathways beneficial for plant growth. Exploration of biosynthetic genes indicated a prevalence of the type-II polyketide synthase gene. Sequencing the ketosynthase-alpha domain of the gene led to predictions of various bioactive secondary metabolites. Around 44% of the isolates demonstrated antimicrobial properties, with some also displaying plant growth-promoting traits. Amycolatopsis SD-15 exhibited promising results in planta when tested on tomato plants. These findings highlight the potential of actinobacteria from Meghalaya's mining sites across medical, agricultural, and industrial domains.

Manipulation and epigenetic control of silent biosynthetic pathways in actinobacteria

Most biosynthetic gene clusters (BGCs) of Actinobacteria are either silent or expressed less than the detectable level. The non-genetic approaches including biological interactions, chemical agents, and physical stresses that can be used to awaken silenced pathways are compared in this paper. These non-genetic induction strategies often need screening approaches, including one strain many compounds (OSMAC), reporter-guided mutant selection, and high throughput elicitor screening (HiTES) have been developed. Different types of genetic manipulations applied in the induction of cryptic BGCs of Actinobacteria can be categorized as genome-wide pleiotropic and targeted approaches like manipulation of global regulatory systems, modulation of regulatory genes, ribosome and engineering of RNA polymerase or phosphopantheteine transferases. Targeted approaches including genome editing by CRISPR, mutation in transcription factors and modification of BGCs promoters, inactivation of the highly expressed biosynthetic pathways, deleting the suppressors or awakening the activators, heterologous expression, or refactoring of gene clusters can be applied for activation of pathways which are predicted to synthesize new bioactive structures in genome mining studies of Acinobacteria. In this review, the challenges and advantages of employing these approaches in induction of Actinobacteria BGCs are discussed. Further, novel natural products needed as drug for pharmaceutical industry or as biofertilizers in agricultural industry can be discovered even from known species of Actinobactera by the innovative approaches of metabolite biosynthesis elicitation.

Anti-MRSA Dimeric and Brominated Phenyltetracenoids Produced by Streptomyces morookaense SC1169

Eleven new phenyltetracenoid polyketides, streptovertimycins U (1) and V (2), 14-bromo-streptovertidione (3), streptovertimycins W-Y (4-6), and streptovertimycins Z1-Z5 (7-11), together with the known congeners fasamycins R (12) and S (13) and accramycins A (14) and B (15), were isolated from the NaBr-supplemented rice-grown cultures of Streptomyces morookaense SC1169. Their structures were elucidated by extensive spectroscopic analysis, single-crystal X-ray diffraction analysis, and theoretical computations of ECD spectra. Compounds 1 and 2 are methylene-bridged dimers of accramycin A, and compounds 3 and 7-11 are brominated fasamycin congeners. Compounds 5 and 8-14 exhibited activity against the drug-resistant bacteria MRSA and VRE (MIC = 0.6-5.0 μg/mL), and the dimer 1 displayed activity against MRSA (MIC = 2.5 μg/mL). Compounds 6-15 showed cytotoxicity against the human carcinoma A549, HeLa, HepG2, and MCF-7 cells in the IC50 range between 1.7 and 9.2 μM.

Deletion of the accramycin pathway-specific regulatory gene accJ activates the production of unrelated polyketide metabolites

The manipulation of regulatory genes has been employed to awaken cryptic metabolites in Streptomyces. Of particular interest in recent years is the effect of disruption of a pathway-specific gene to other biosynthetic pathways. Herein, we report the inactivation of the accramycin pathway-specific regulatory gene, accJ in Streptomyces sp. MA37 resulted in the production of unrelated polyketide metabolites. Through detailed mass spectrometric and spectroscopic analyses, and comparison with literature data, their structures were deduced as 3-methoxy-2-methyl-4H-pyran-4-one (1), zanthopyranone (2), propioveratrone (3), and TW94a (4). To the best of our knowledge, this is the first report of the isolation of 1-3 from bacteria. Compounds 1, 2, and 4 showed weak to moderate activity against Staphylococcus aureus, Enterococcus faecalis, and Enterococcus faecium. Propioveratrone (3) displayed better inhibitory activity (MIC = 6.3 μg/mL) than ampicillin against multi-drug resistant E. faecium K60-39 clinical isolate (MIC = 25 μg/mL), suggesting a promising structural template for the drug development targeting Enterococcus isolates.

Heterologous Expression of the Formicamycin Biosynthetic Gene Cluster Unveils Glycosylated Fasamycin Congeners

Formicamycins and their biosynthetic intermediates the fasamycins are polyketide antibiotics produced by Streptomyces formicae KY5 from a pathway encoded by the for biosynthetic gene cluster. In this work the ability of Streptomyces coelicolor M1146 and the ability of Saccharopolyspora erythraea Δery to heterologously express the for biosynthetic gene cluster were assessed. This led to the identification of eight new glycosylated fasamycins modified at different phenolic groups with either a monosaccharide (glucose, galactose, or glucuronic acid) or a disaccharide comprised of a proximal hexose (either glucose or galactose), with a terminal pentose (arabinose) moiety. In contrast to the respective aglycones, minimal inhibitory screening assays showed these glycosylated congeners lacked antibacterial activity.

Discovery of glycosylated naphthacemycins and elucidation of the glycosylation

Two glycosylated naphthacemycins (naphthacemycins D₁ and D₂) were identified in Streptomyces sp. N12W1565. These two compounds not only showed antimicrobial potential against bacteria but also exhibited more aqueous solubility than naphthacemycins. Furthermore, the whole genome of Streptomyces sp. N12W1565 has been sequenced, the natY gene, located outside the biosynthetic gene cluster encoding a D-glucose glycosyltransferase, was identified to mediate glycosylation in the phenolic hydroxyl of the naphthacemycin core scaffold. Glycosyltransferase was elucidated in vitro by using a homologous enzyme, which showed potential as a biocatalyst.

Expanding the Chemical Diversity of Fasamycin Via Genome Mining and Biocatalysis

Genome mining and biocatalytic modification of chemical structures are critical methods to develop new antibiotics. In this study, eight new fasamycins (3, 4, 6, and 8-12) along with five known analogues (1, 2, 5, 7, and 13) were obtained by the overexpression of two phosphopantetheinyl transferases (PPtases) in Streptomyces kanamyceticus and biocatalytic transformation with two halogenases. These new compounds displayed significant activity against Staphylococcus aureus and Bacillus subtilis, in particular, C-29-methyl and C-2/C-22-halogen derivatives. This study increases the chemical diversity of bioactive fasamycin derivatives and provides useful halogenation tools for engineering their scaffolds.

Beyond Soil-Dwelling Actinobacteria: Fantastic Antibiotics and Where to Find Them

Bacterial secondary metabolites represent an invaluable source of bioactive molecules for the pharmaceutical and agrochemical industries. Although screening campaigns for the discovery of new compounds have traditionally been strongly biased towards the study of soil-dwelling Actinobacteria, the current antibiotic resistance and discovery crisis has brought a considerable amount of attention to the study of previously neglected bacterial sources of secondary metabolites. The development and application of new screening, sequencing, genetic manipulation, cultivation and bioinformatic techniques have revealed several other groups of bacteria as producers of striking chemical novelty. Biosynthetic machineries evolved from independent taxonomic origins and under completely different ecological requirements and selective pressures are responsible for these structural innovations. In this review, we summarize the most important discoveries related to secondary metabolites from alternative bacterial sources, trying to provide the reader with a broad perspective on how technical novelties have facilitated the access to the bacterial metabolic dark matter.

Total Synthesis of Streptovertidione and Bioinspired Transformation to Streptovertidine A and Formicapyridine A

We report herein a concise total synthesis of streptovertidione, and its transformation to streptovertidine A and formicapyridine A through a bioinspired pyridination. This stratage features: 1) a one-pot Ti(O-iPr)4-mediated photoenolization/Diels-Alder...

Isolation of a new Streptomyces virginiae W18 against fish pathogens and its effect on disease resistance mechanism of Carassius auratus

The Streptomyces virginiae strain W18 was screened from soil, which exhibited broad-spectrum antibacterial activity against fish pathogens. Safety assays showed that strain W18 had no toxicity to fish. Additionally, strain W18 promoted the growth performance of Carassius auratus after feeding in feed mixed with bacteria for one month. Moreover, the activities of AKP, ACP, and SOD in the serum of C. auratus were significantly increased, while the activity of LZM did not greatly change. To detect the expression levels of the genes related to immune factors in the livers, kidneys, and spleens of C. auratus, qRT-PCR was performed. The expression levels of KEAP1, IL-8, TNF-α, IL-β, and C3 were upregulated in all three organs compared to the control, but LZM expression was downregulated in the kidney. The challenge experiment illustrated that the probability of infection with Aeromonas veronii was reduced by 60% and 40% when C. auratus was fed with two different doses of strain W18 in advance. The whole genome of strain W18 was sequenced, and the gene clusters of secondary metabolites in strain W18 were analyzed by AntiSMASH. The results showed that strain W18 contained a total of 26 gene clusters, and functional annotation analysis was conducted by using the non-coding databases COG and KEGG. All of the above results indicated that the use of strain W18 as a feed additive could enhance the resistance of C. auratus toward pathogenic bacteria and disease. In conclusion, an antagonistic strain (W18) against fish pathogenic bacteria was obtained in this study, which is of great significance for finding new treatment methods for bacterial diseases in the aquaculture industry.

Antibacterial and Cytotoxic Phenyltetracenoid Polyketides from Streptomyces morookaense

Formicapyridine-type racemates, streptovertidines A (1) and B (2), a 7,24-seco-fasamycin, streptovertidione (3), and the fasamycin-type streptovertimycins I-T (4-15), together with 13 known fasamycin congeners (16-28), were isolated from soil-derived Streptomyces morookaense SC1169. Their structures were elucidated by extensive spectroscopic analysis and theoretical computations of ECD spectra. The fasamycin-type compounds 5, 8-12, 14, and 15 exhibited activity against the drug-resistant bacteria MRSA and VRE (MIC: 1.25-10.0 μg/mL). All isolates, except 3, 4, 10, and 24, displayed cytotoxicity against at least one of the human carcinoma A549, HeLa, HepG2, and MCF-7 cells (IC₅₀ < 10.0 μM), of which some were also cytotoxic to the noncancerous Vero cells. Taken together, the activity data demonstrated that the fasamycin-type compounds were more selective to the tested bacteria over the mammalian cells. Structure-activity relationship analysis suggested that chlorination at C-2 in antibacterial fasamycin-type compounds improves the activity and selectivity to the bacteria. Theoretical simulations of reaction paths and chemical reactions for conversion of 3 to 1 were carried out and supported that the pyridine ring formation in formicapyridines proceeds nonenzymatically via 1,5-dicarbonyl condensation with ammonia.