Monacyclinones, New Angucyclinone Metabolites Isolated from Streptomyces sp. M7_15 Associated with the Puerto Rican Sponge Scopalina ruetzleri

Marine actinomycetes-derived angucyclines and angucyclinones with biosynthesis and activity--past 10 years (2014-2023)

Actinomycete bacteria derived from marine environments are a good source of natural products with diverse biological activities such as cytotoxicity, antiviral, and antimicrobial actions. This review summarizes 191 angucyclines and angucyclinones derived from marine actinomycetes reported in the literature from 2014 to 2023 and introduced the latest developments in actinomycete-silenced biosynthetic gene cluster activation, including heterologous recombination and in situ activation. The key role of redox post-modifications in the biosynthetic process of atypical angucyclines. This review provides insights into the discovery and biosynthesis of valuable angucyclines and angucyclinones from marine-associated actinomycetes and potential lead compounds for the research and development of new drugs.

Mini review: antimicrobial compounds produced by bacteria associated with marine invertebrates

The marine environment is considered one of the most important ecosystems with high biodiversity. Microorganisms in this environment are variable and coexist with other marine organisms. The microbes associated with other marine organisms produce compounds with biological activity that may help the host's defense against invading organisms. The symbiotic association of bacteria with marine invertebrates is of ecological and biotechnological importance. Biologically active metabolites isolated from bacteria associated with marine invertebrates are considered potential sources of natural antimicrobial molecules for treating infectious diseases. Many studies have been conducted to screen the antimicrobial activity of metabolites produced by bacteria associated with marine invertebrates. This work provides an overview of the advancements in antimicrobial compound research on bacteria associated with marine invertebrates.

Advances in Natural Products from the Marine-Sponge-Associated Microorganisms with Antimicrobial Activity in the Last Decade

Microorganisms are the dominating source of food and nutrition for sponges and play an important role in sponge structure, chemical defense, excretion and evolution. In recent years, plentiful secondary metabolites with novel structures and specific activities have been identified from sponge-associated microorganisms. Additionally, as the phenomenon of the drug resistance of pathogenic bacteria is becoming more and more common, it is urgent to discover new antimicrobial agents. In this paper, we reviewed 270 secondary metabolites with potential antimicrobial activity against a variety of pathogenic strains reported in the literature from 2012 to 2022. Among them, 68.5% were derived from fungi, 23.3% originated from actinomycetes, 3.7% were obtained from other bacteria and 4.4% were discovered using the co-culture method. The structures of these compounds include terpenoids (13%), polyketides (51.9%), alkaloids (17.4%), peptides (11.5%), glucosides (3.3%), etc. Significantly, there are 124 new compounds and 146 known compounds, 55 of which have antifungal activity in addition to antipathogenic bacteria. This review will provide a theoretical basis for the further development of antimicrobial drugs.

Anticancer Activities of Marine-Derived Phenolic Compounds and Their Derivatives

Since the middle of the last century, marine organisms have been identified as producers of chemically and biologically diverse secondary metabolites which have exerted various biological activities including anticancer, anti-inflammatory, antioxidant, antimicrobial, antifouling and others. This review primarily focuses on the marine phenolic compounds and their derivatives with potent anticancer activity, isolated and/or modified in the last decade. Reports on the elucidation of their structures as well as biosynthetic studies and total synthesis are also covered. Presented phenolic compounds inhibited cancer cells proliferation or migration, at sub-micromolar or nanomolar concentrations (lamellarins D (37), M (38), K (39), aspergiolide B (41), fradimycin B (62), makulavamine J (66), mayamycin (69), N-acetyl-N-demethylmayamycin (70) or norhierridin B (75)). In addition, they exhibited anticancer properties by a diverse biological mechanism including induction of apoptosis or inhibition of cell migration and invasive potential. Finally, phlorotannins 1–7 and bromophenols 12–29 represent the most researched phenolic compounds, of which the former are recognized as protective agents against UVB or gamma radiation-induced skin damages. Finally, phenolic metabolites were assorted into six main classes: phlorotannins, bromophenols, flavonoids, coumarins, terpenophenolics, quinones and hydroquinones. The derivatives that could not be attributed to any of the above-mentioned classes were grouped in a separate class named miscellaneous compounds.

Cytotoxic compounds from marine actinomycetes: Sources, Structures and Bioactivity

Marine actinomycetes produce a substantial number of natural products with cytotoxic activity. The strains of actinomycetes were isolated from different sources like fishes, coral, sponges, seaweeds, mangroves, sediments etc. These cytotoxic compounds can be categorized briefly into four classes: polyketides, non-ribosomal peptides and hybrids, isoprenoids and hybrids, and others, among which majority are polyketides (146). Twenty two out of the 254 compounds showed potent cytotoxicity with IC₅₀ values at ng/mL or nM level. This review highlights the sources, structures and antitumor activity of 254 natural products isolated from marine actinomycetes, which were new when they were reported from 1989 to 2020.

Natural Products from Actinomycetes Associated with Marine Organisms

The actinomycetes have proven to be a rich source of bioactive secondary metabolites and play a critical role in the development of pharmaceutical researches. With interactions of host organisms and having special ecological status, the actinomycetes associated with marine animals, marine plants, macroalgae, cyanobacteria, and lichens have more potential to produce active metabolites acting as chemical defenses to protect the host from predators as well as microbial infection. This review focuses on 536 secondary metabolites (SMs) from actinomycetes associated with these marine organisms covering the literature to mid-2021, which will highlight the taxonomic diversity of actinomycetes and the structural classes, biological activities of SMs. Among all the actinomycetes listed, members of Streptomyces (68%), Micromonospora (6%), and Nocardiopsis (3%) are dominant producers of secondary metabolites. Additionally, alkaloids (37%), polyketides (33%), and peptides (15%) comprise the largest proportion of natural products with mostly antimicrobial activity and cytotoxicity. Furthermore, the data analysis and clinical information of SMs have been summarized in this article, suggesting that some of these actinomycetes with multiple host organisms deserve more attention to their special ecological status and genetic factors.

A Novel 4H-Chromen-4-One Derivative from Marine Streptomyces ovatisporus S4702T as Potential Antibacterial and Anti-Cancer Agent

BACKGROUND

Marine actinomycetes are among indispensable sources of natural bioactive compounds with unique antimicrobial and anti-cancer activities.

OBJECTIVE

Herein, it was aimed to elucidate bioactive potential of a marine-derived Streptomyces ovatisporus S4702T, isolated previously.

METHODS

Streptomyces ovatisporus S4702T was cultured in N-Z Amine broth and extraction was carried out using different organic solvents. Bioassay guided purification was followed by chemical characterization using NMR and LC-MS/MS. The compound was then evaluated for its antibacterial, antioxidant and cytotoxic activities.

RESULTS

Etyl acetate extracts gave the highest antibacterial activity and chemical characterization of this extract indicated the formula as C15H29O5N3 and the corresponding possible molecular structure as 4H-chromen-4-one derivative. It was found highly potent against Bacillus subtilis ATCC 6633 (MIC: 0.25 µg ml-1) and Micrococcus luteus ATCC 9341 (MBC: 0.5 µg ml-1). It has no remarkable antioxidant activity, but higher EC50 value and less cytotoxicity against normal cells. The EC50 values of this chromen derivative were found as 9.68 µg ml-1 for human colon carcinoma, 9.93 µg ml-1 for human prostate adenocarcinoma and 25.5 µg ml-1 for human embryonic kidney cells.

CONCLUSION

Overall, the presented 4H-chromen-4-one derivative is a remarkable bioactive compound with potent antibacterial and cytotoxic activity. With its high bioactive potential, it is proposed as a good candidate in medicine.

Monacycliones G-K and ent-Gephyromycin A, Angucycline Derivatives from the Marine-Derived Streptomyces sp. HDN15129

Six new angucycline derivatives, named monacycliones G-K (1-5) and ent-gephyromycin A (6), as well as three known ones (7-9) were discovered from the marine sediment-derived actinomycete Streptomyces sp. HDN15129 guided by Global Natural Products Social (GNPS) molecular networking. Structures including absolute configurations were elucidated by extensive NMR, MS, and ECD analyses. Among them, monacyclione G (1) possesses a unique scaffold featuring a xanthone core linked to the aminodeoxysugar ossamine, and monacycliones H-J (2-4) are rare examples of natural angucyclines with an S-methyl group. Monacycliones I and J (3 and 4) showed cytotoxic activity against multiple human cancer cell lines, with IC₅₀ values ranging from 3.5 to 10 μM.

Microorganisms Associated with the Marine Sponge Scopalina hapalia: A Reservoir of Bioactive Molecules to Slow Down the Aging Process

Aging research aims at developing therapies that delay normal aging processes and some related pathologies. Recently, many compounds and extracts from natural products have been shown to slow aging and/or extend lifespan. Marine sponges and their associated microorganisms have been found to produce a wide variety of bioactive secondary metabolites; however, those from the Southwest of the Indian Ocean are much less studied, especially regarding anti-aging activities. In this study, the microbial diversity of the marine sponge Scopalina hapalia was investigated by metagenomic analysis. Twenty-six bacterial and two archaeal phyla were recovered from the sponge, of which the Proteobacteria phylum was the most abundant. In addition, 30 isolates from S. hapalia were selected and cultivated for identification and secondary metabolites production. The selected isolates were affiliated to the genera Bacillus, Micromonospora, Rhodoccocus, Salinispora, Aspergillus, Chaetomium, Nigrospora and unidentified genera related to the family Thermoactinomycetaceae. Crude extracts from selected microbial cultures were found to be active against seven clinically relevant targets (elastase, tyrosinase, catalase, sirtuin 1, Cyclin-dependent kinase 7 (CDK7), Fyn kinase and proteasome). These results highlight the potential of microorganisms associated with a marine sponge from Mayotte to produce anti-aging compounds. Future work will focus on the isolation and the characterization of bioactive compounds.

Sponges from Zanzibar host diverse prokaryotic communities with potential for natural product synthesis

Sponges are one of the most dominant organisms in marine ecosystems. One reason for their success is their association with microorganisms that are besides the host itself responsible for the chemical defence. Sponge abundances have been increasing on coral reefs in the Western Indian Ocean (WIO) and are predicted to increase further with rising anthropogenic impacts on coral reefs. However, there is a paucity of information on chemical ecology of sponges from the WIO and their prokaryotic community composition. We used a combination of Illumina sequencing and a predictive metagenomic analysis to (i) assess the prokaryotic community composition of sponges from Zanzibar, (ii) predict the presence of KEGG metabolic pathways responsible for bioactive compound production and (iii) relate their presence to the degree of observed chemical defence in their respective sponge host. We found that sponges from Zanzibar host diverse prokaryotic communities that are host species-specific. Sponge-species and respective specimens that showed strong chemical defences in previous studies were also predicted to be highly enriched in various pathways responsible for secondary metabolite production. Hence, the combined sequencing and predictive metagenomic approach proved to be a useful indicator for the metabolic potential of sponge holobionts.

Marine Natural Products with High Anticancer Activities

This review covers recent literature from 2012-2019 concerning 170 marine natural products and their semisynthetic analogues with strong anticancer biological activities. Reports that shed light on cellular and molecular mechanisms and biological functions of these compounds, thus advancing the understanding in cancer biology are also included. Biosynthetic studies and total syntheses, which have provided access to derivatives and have contributed to the proper structure or stereochemistry elucidation or revision are mentioned. The natural compounds isolated from marine organisms are divided into nine groups, namely: alkaloids, sterols and steroids, glycosides, terpenes and terpenoids, macrolides, polypeptides, quinones, phenols and polyphenols, and miscellaneous products. An emphasis is placed on several drugs originating from marine natural products that have already been marketed or are currently in clinical trials.

Biological and Chemical Diversity of Marine Sponge-Derived Microorganisms over the Last Two Decades from 1998 to 2017

Marine sponges are well known as rich sources of biologically natural products. Growing evidence indicates that sponges harbor a wealth of microorganisms in their bodies, which are likely to be the true producers of bioactive secondary metabolites. In order to promote the study of natural product chemistry and explore the relationship between microorganisms and their sponge hosts, in this review, we give a comprehensive overview of the structures, sources, and activities of the 774 new marine natural products from sponge-derived microorganisms described over the last two decades from 1998 to 2017.

Marine Actinomycetes-derived Natural Products

Actinomycetes is an abundant resource for discovering a large number of lead compounds, which play an important role in microbial drug discovery. Compared to terrestrial microorganisms, marine actinomycetes have unique metabolic pathways because of their special living environment, which has the potential to produce a variety of bioactive substances. In this paper, secondary metabolites isolated from marine actinomycetes are reviewed (2013-2018), most of which exhibited cytotoxic, antibacterial, and antiviral biological activities.

Cloning and identification of the Frigocyclinone biosynthetic gene cluster from Streptomyces griseus strain NTK 97

Frigocyclinone is a novel antibiotic with antibacterial and anticancer activities. It is produced by both Antarctica-derived Streptomyces griseus NTK 97 and marine sponge-associated Streptomyces sp. M7_15. Here, we first report the biosynthetic gene cluster of frigocyclinone in the S. griseus NTK 97. The frigocyclinone gene cluster spans a DNA region of 33-kb which consists of 30 open reading frames (ORFs), encoding minimal type II polyketide synthase, aromatase and cyclase, redox tailoring enzymes, sugar biosynthesis-related enzymes, C-glycosyltransferase, a resistance protein, and three regulatory proteins. Based on the bioinformatic analysis, a biosynthetic pathway for frigocyclinone was proposed. Second, to verify the cloned gene cluster, CRISPR-Cpf1 mediated gene disruption was conducted. Mutant with the disruption of beta-ketoacyl synthase encoding gene frig20 fully loses the ability of producing frigocyclinone, while inactivating the glycosyltransferase gene frig1 leads to the production of key intermediate of anti-MRSA anthraquinone tetrangomycin.

Cytotoxic, Anti-Migration, and Anti-Invasion Activities on Breast Cancer Cells of Angucycline Glycosides Isolated from a Marine-Derived Streptomyces sp

Four angucycline glycosides were previously characterized from marine-derived Streptomyces sp. OC1610.4. Further investigation of this strain cultured on different fermentation media from that used previously resulted in the isolation of two new angucycline glycosides, vineomycins E and F (1–2), and five known homologues, grincamycin L (3), vineomycinone B₂ (4), fridamycin D (5), moromycin B (7), and saquayamycin B₁ (8). Vineomycin F (2) contains an unusual ring-cleavage deoxy sugar. All the angucycline glycosides isolated from Streptomyces sp. OC1610.4 were evaluated for their cytotoxic activity against breast cancer cells MCF-7, MDA-MB-231, and BT-474. Moromycin B (7), saquayamycin B₁ (8), and saquayamycin B (9) displayed potent anti-proliferation against the tested cell lines, with IC₅₀ values ranging from 0.16 to 0.67 μM. Saquayamycin B (9) inhibited the migration and invasion of MDA-MB-231 cells in a dose-dependent manner, as detected by Transwell and wound-healing assays.

Metagenomics Approaches in Discovery and Development of New Bioactive Compounds from Marine Actinomycetes

Marine actinomycetes are prolific sources of marine drug discovery system contributing for several bioactive compounds of biomedical prominence. Metagenomics, a culture-independent technique through its sequence- and function-based screening has led to the discovery and synthesis of numerous biologically significant compounds like polyketide synthase, Non-ribosomal peptide synthetase, antibiotics, and biocatalyst. While metagenomics offers different advantages over conventional sequencing techniques, they also have certain limitations including bias classification, non-availability of quality DNA samples, heterologous expression, and host selection. The assimilation of advanced amplification and screening methods such as φ29 DNA polymerase, Next-Generation Sequencing, Cosmids, and recent bioinformatics tools like automated genome mining, anti-SMASH have shown promising results to overcome these constrains. Consequently, functional genomics and bioinformatics along with synthetic biology will be crucial for the success of the metagenomic approach and indeed for exploring new possibilities among the microbial consortia for the future drug discovery process.

Naturally occurring of α,β-diepoxy-containing compounds: origin, structures, and biological activities

Diepoxy-containing compounds are widely distributed in nature. These metabolites are found in plants and marine organisms and are also produced by many microorganisms, fungi, or fungal endophytes. Many of these metabolites are antibiotics and exhibit a wide variety of biological activities. More than 80 α,β-diepoxy-containing compounds are presented in this article, which belong to different classes of chemical compounds including lipids, terpenoids, alkaloids, quinones, hydroquinones, and pyrones. The main activities that characterize α,β-diepoxy-containing compounds are antineoplastic with confidence up to 99%, antifungal with confidence up to 94%, antiinflammatory with confidence up to 92%, or antibacterial with confidence up to 78%. In addition, these metabolites can be used as a lipid metabolism regulator with a certainty of up to 81%, antiviral (Arbovirus) activity with a certainty of up to 71%, or antiallergic activity with confidence up to 69%. These data on the biological activity of diepoxy-containing compounds are of considerable interest to pharmacologists, chemists, and medical professionals who are involved in phytomedicine and related areas of science and industry.

New bioactive metabolites from the elicited marine sponge-derived bacterium Actinokineospora spheciospongiae sp. nov

Several approaches have been dedicated to activate the cryptic gene clusters in the genomes of actinomycetes for the targeted discovery of new fascinating biomedical lead structures. In the current study, N-acetylglucosamine was used to maximize the chemical diversity of sponge-derived actinomycete Actinokineospora spheciospongiae sp. nov. HR-ESI-MS was employed for dereplication study and orthogonal partial least square-discriminant analysis was applied to evaluate the HR-ESI-MS data of the different fractions. As a result, two new fridamycins H (1) and I (2), along with three known compounds actinosporin C (3), D (4), and G (5) were isolated from the solid culture of sponge-associated actinomycete Actinokineospora spheciospongiae sp. nov., elicited with N-acetylglucosamine. Characterization of the isolated compounds was pursued using mass spectrometry and NMR spectral data. Fridamycin H (1) exhibited significant growth inhibitory activity towards Trypanosoma brucei strain TC221. These results highlight the potential of elicitation in sponge-associated actinomycetes as an effective strategy for the discovery of new anti-infective natural products.

Isolation and characterization of novel antibacterial compound from an untapped plant, Stereospermum fimbriatum

Stereospermum fimbriatum or locally known as "Chicha" is traditionally used for itchy skin, earache, stomachache and postpartum treatments. This study was designed to evaluate the antimicrobial potential of S. fimbriatum's stem bark against 11 pathogens and isolate its bioactive compound. Successive soxhlet extraction was conducted using n-hexane, dichloromethane (DCM) and methanol. Disc diffusion, minimum inhibitory and bactericidal concentration (MIC & MBC) assays were done to examine the antimicrobial activity. Bioassay-guided isolation was conducted on S. fimbriatum's extract. The DCM extract of stem bark (DS) was the most potent extract followed by n-hexane extract of the stem bark (NS). A novel compound was isolated and coded as C1 which demonstrated potent antibacterial effects with the MIC values as low as 3.13 µg/mL to 6.25 µg/mL, against S. epidermidis, MRSA and S. aureus. Thus, S. fimbriatum could be a potential source of antimicrobial agents for the treatment of skin infections, specifically, MRSA.

Marine natural products

Covering: 2015. Previous review: Nat. Prod. Rep., 2016, 33, 382-431This review covers the literature published in 2015 for marine natural products (MNPs), with 1220 citations (792 for the period January to December 2015) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1340 in 429 papers for 2015), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.

Marine Sponge-Derived Streptomyces sp. SBT343 Extract Inhibits Staphylococcal Biofilm Formation

Staphylococcus epidermidis and Staphylococcus aureus are opportunistic pathogens that cause nosocomial and chronic biofilm-associated infections. Indwelling medical devices and contact lenses are ideal ecological niches for formation of staphylococcal biofilms. Bacteria within biofilms are known to display reduced susceptibilities to antimicrobials and are protected from the host immune system. High rates of acquired antibiotic resistances in staphylococci and other biofilm-forming bacteria further hamper treatment options and highlight the need for new anti-biofilm strategies. Here, we aimed to evaluate the potential of marine sponge-derived actinomycetes in inhibiting biofilm formation of several strains of S. epidermidis, S. aureus, and Pseudomonas aeruginosa. Results from in vitro biofilm-formation assays, as well as scanning electron and confocal microscopy, revealed that an organic extract derived from the marine sponge-associated bacterium Streptomyces sp. SBT343 significantly inhibited staphylococcal biofilm formation on polystyrene, glass and contact lens surfaces, without affecting bacterial growth. The extract also displayed similar antagonistic effects towards the biofilm formation of other S. epidermidis and S. aureus strains tested but had no inhibitory effects towards Pseudomonas biofilms. Interestingly the extract, at lower effective concentrations, did not exhibit cytotoxic effects on mouse fibroblast, macrophage and human corneal epithelial cell lines. Chemical analysis by High Resolution Fourier Transform Mass Spectrometry (HRMS) of the Streptomyces sp. SBT343 extract proportion revealed its chemical richness and complexity. Preliminary physico-chemical characterization of the extract highlighted the heat-stable and non-proteinaceous nature of the active component(s). The combined data suggest that the Streptomyces sp. SBT343 extract selectively inhibits staphylococcal biofilm formation without interfering with bacterial cell viability. Due to absence of cell toxicity, the extract might represent a good starting material to develop a future remedy to block staphylococcal biofilm formation on contact lenses and thereby to prevent intractable contact lens-mediated ocular infections.

Emerging biopharmaceuticals from marine actinobacteria

Actinobacteria are quotidian microorganisms in the marine world, playing a crucial ecological role in the recycling of refractory biomaterials and producing novel secondary metabolites with pharmaceutical applications. Actinobacteria have been isolated from the huge area of marine organisms including sponges, tunicates, corals, mollusks, crabs, mangroves and seaweeds. Natural products investigation of the marine actinobacteria revealed that they can synthesize numerous natural products including alkaloids, polyketides, peptides, isoprenoids, phenazines, sterols, and others. These natural products have a potential to provide future drugs against crucial diseases like cancer, HIV, microbial and protozoal infections and severe inflammations. Therefore, marine actinobacteria portray as a pivotal resource for marine drugs. It is an upcoming field of research to probe a novel and pharmaceutically important secondary metabolites from marine actinobacteria. In this review, we attempt to summarize the present knowledge on the diversity, chemistry and mechanism of action of marine actinobacteria-derived secondary metabolites from 2007 to 2016.