Iseolides A–C, antifungal macrolides from a coral-derived actinomycete of the genus Streptomyces

Marine Ascomycetes Extract Antifungal Susceptibility against Candida spp. Isolates from Oral Candidiasis HIV/AIDS Patient: An In Vitro Study

OBJECTIVE

 The etiology of oral candidiasis (OC) was Candida albicans, C. krusei, C. dubliniensis, C. tropicalis that are frequently found in human immunodeficiency virus/ acquired immunodeficiency syndrome (HIV/AIDS) patients. Marine ascomycetes (MA) have been widely reported as an important producer of various antibiotic compounds. However, there is limited study of antifungal compounds from MA against Candida species. The aim of this study was to investigate the antifungal susceptibility of MA against Candida spp. isolates from OC HIV/AIDS patient.

MATERIALS AND METHODS

 Trichoderma sp. is a sponge-associated fungus collected from Karimunjawa National Park, Central Java, Indonesia. The validation of C. albicans, C. krusei, C. dubliniensis, C. tropicalis. was done by ChromAgar. This study was true experimental with post-test only control group design; the sample was four replications for each group. Nystatin administration (K +), the golden standard antifungal drug, was used. The minimum fungicidal concentration (MFC), minimum inhibitory concentration (MIC), and diffusion zone methods were done. Analysis of variance difference test, and post-hoc Tukey's honest significant different were done to analyze the significant different between groups (p ≤ 0.05).

RESULTS

 The MFC and MIC of MA against C. albicans, C. krusei, C. dubliniensis, and C. tropicalis were found at 12.5%. In addition, the greatest diffusion zone of MA against C. albicans, C. krusei, C. dubliniensis, and C. tropicalis was found at 12.5%. There is no appreciable difference in antifungal activity between K + and 12.5% of MA extract (p ≥ 0.05).

CONCLUSION

 Concentration of 12.5% MA extract has antifungal susceptibility against Candida spp. isolates from OC HIV/AIDS patient.

Streptomyces: a natural source of anti-Candida agents

Introduction. There is an urgent need to source new compounds that can combat the current threat of serious infection caused by Candida spp. and contend with the problem of antimicrobial resistance.

Gap. A synthesis of the evidence available from the current literature is needed to identify promising antifungal chemotherapeutics.

Aim. To highlight anti-Candida compounds derived from Streptomyces spp. (a well-known source of antimicrobial compounds) that could translate to potential candidates for future clinical practice.

Methodology. A comprehensive review was conducted across three scientific literature databases spanning a 13-year period.

Results. We identified 151 compounds with anti-Candida activity. Amongst these, 40 were reported with very strong inhibitory activity, having minimum inhibitory concentrations (MICs) against Candida spp. of <3.5 µg ml−1, 66 compounds were considered strong inhibitors and 45 compounds exhibited moderate inhibitory potential. From an analysis of the MICs, we deduced that the actinomycin-like compounds RSP01 and RSP02 were probably the most promising anti-Candida compounds. Other antifungals of note included filipin-like compounds, which demonstrated superior inhibition to amphotericin B and activity against Candida glabrata and Candida krusei, and bafilomycin derivatives, which had substantial inhibition against Candida parapsilosis.

Conclusion. It is essential to recognize the limitations inherent in the quest for new antifungals, which encompass toxicity, in vivo effectiveness and constraints associated with limited data access. However, further investigation through in-depth study and emerging technologies is of paramount importance, given that there are still many more compounds to discover. This review highlights the importance of antifungal compounds derived from Streptomyces , which demonstrate robust inhibition, and, in many cases, low toxicity, making them promising candidates for the development of novel antifungal agents.

Natural Polyketides Act as Promising Antifungal Agents

Invasive fungal infections present a significant risk to human health. The current arsenal of antifungal drugs is hindered by drug resistance, limited antifungal range, inadequate safety profiles, and low oral bioavailability. Consequently, there is an urgent imperative to develop novel antifungal medications for clinical application. This comprehensive review provides a summary of the antifungal properties and mechanisms exhibited by natural polyketides, encompassing macrolide polyethers, polyether polyketides, xanthone polyketides, linear polyketides, hybrid polyketide non-ribosomal peptides, and pyridine derivatives. Investigating natural polyketide compounds and their derivatives has demonstrated their remarkable efficacy and promising clinical application as antifungal agents.

Iseoic acids and bisiseoate: three new naphthohydroquinone/naphthoquinone-class metabolites from a coral-derived Streptomyces

Two new naphthohydroquinone derivatives designated iseoic acids A (1) and B (2) and a new symmetrical glycerol bisester of naphthoquinonepropanoic acid designated bisiseoate (3) were isolated from the culture extract of a marine-derived actinomycete Streptomyces sp. DC4-5. The structures of 1-3 were determined by analyzing one- and two-dimensional NMR data and MS analytical data. The absolute configurations were determined by NOESY analysis and the phenylglycine methyl ester (PGME) method for 1 and by considering the structural similarity and biosynthesis for 2 and 3. Compound 3 exhibited modest cytotoxicity against P388 murine leukemia cells with an IC50 value of 19 μM.

Anti-Candidal Marine Natural Products: A Review

Candida spp. are common opportunistic microorganisms in the human body and can cause mucosal, cutaneous, and systemic infections, mainly in individuals with weakened immune systems. Candida albicans is the most isolated and pathogenic species; however, multi-drug-resistant yeasts like Candida auris have recently been found in many different regions of the world. The increasing development of resistance to common antifungals by Candida species limits the therapeutic options. In light of this, the present review attempts to discuss the significance of marine natural products in controlling the proliferation and metabolism of C. albicans and non-albicans species. Natural compounds produced by sponges, algae, sea cucumber, bacteria, fungi, and other marine organisms have been the subject of numerous studies since the 1980s, with the discovery of several products with different chemical frameworks that can inhibit Candida spp., including antifungal drug-resistant strains. Sponges fall under the topmost category when compared to all other organisms investigated. Terpenoids, sterols, and alkaloids from this group exhibit a wide array of inhibitory activity against different Candida species. Especially, hippolide J, a pair of enantiomeric sesterterpenoids isolated from the marine sponge Hippospongia lachne, exhibited strong activity against Candida albicans, Candida parapsilosis, and Candida glabrata. In addition, a comprehensive analysis was performed to unveil the mechanisms of action and synergistic activity of marine products with conventional antifungals. In general, the results of this review show that the majority of chemicals derived from the marine environment are able to control particular functions of microorganisms belonging to the Candida genus, which can provide insights into designing new anti-candidal therapies.

Halo- and Thiocarbazomycins from Coral- and Coral Reef Sands-Derived Actinomycetes

Four actinomycete strains isolated from the coral Acropora austera and coral sand samples from the South China Sea, were found to produce a series of halogenated compounds baring similar ultraviolet absorption based on the analysis of HPLC and LC-MS. The production titers of halogenated compounds from Streptomyces diacarni SCSIO 64983 exceeded those of other similar strains leading us to focus on SCSIO 64983. Four new thiocarbazomycins A–B (1–2), chlocarbazomycin E (3), and brocarbazomycin A (4), together with three known chlocarbazomycins A–C (5–7) containing a carbazole core were identified, and their structures were determined using a combination of spectroscopic analysis including HRESIMS, 1D and 2D NMR. Structurally speaking, compounds 1 and 2 have the rare sulfur-containing carbazole nuclei, and 3 and 4 contain Cl and Br atoms, respectively. Although these compounds have not yet been found to have obvious biological activity, their discovery highlights the role of molecular libraries in subsequent drug discovery campaigns.

Marine Actinomycetes Associated with Stony Corals: A Potential Hotspot for Specialized Metabolites

Microbial secondary metabolites are an important source of antibiotics currently available for combating drug-resistant pathogens. These important secondary metabolites are produced by various microorganisms, including Actinobacteria. Actinobacteria have a colossal genome with a wide array of genes that code for several bioactive metabolites and enzymes. Numerous studies have reported the isolation and screening of millions of strains of actinomycetes from various habitats for specialized metabolites worldwide. Looking at the extent of the importance of actinomycetes in various fields, corals are highlighted as a potential hotspot for untapped secondary metabolites and new bioactive metabolites. Unfortunately, knowledge about the diversity, distribution and biochemistry of marine actinomycetes compared to hard corals is limited. In this review, we aim to summarize the recent knowledge on the isolation, diversity, distribution and discovery of natural compounds from marine actinomycetes associated with hard corals. A total of 11 new species of actinomycetes, representing nine different families of actinomycetes, were recovered from hard corals during the period from 2007 to 2022. In addition, this study examined a total of 13 new compounds produced by five genera of actinomycetes reported from 2017 to 2022 with antibacterial, antifungal and cytotoxic activities. Coral-derived actinomycetes have different mechanisms of action against their competitors.

Marine natural products

Covering: 2020This review covers the literature published in 2020 for marine natural products (MNPs), with 757 citations (747 for the period January to December 2020) 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 (1407 in 420 papers for 2020), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. A meta analysis of bioactivity data relating to new MNPs reported over the last five years is also presented.

Streptomyces corallincola and Kineosporia corallincola sp. nov., two new coral-derived marine actinobacteria

Two new marine actinobacteria, designated as J2-1^T and J2-2^T, were isolated from a coral, Favites pentagona, collected from Rayong Province, Thailand. The taxonomic positions of the two strains were identified based on polyphasic taxonomy. Based on morphological characteristics and chemotaxonomy, strains J2-1^T and J2-2^T were identified as members of the genus Streptomyces and Kineosporia, respectively. Strains J2-1^T and J2-2^T showed the highest 16S rRNA gene sequence similarity to Streptomyces broussonetiae T44^T (98.62 %) and Kineosporia babensis VN05A0415^T (98.08 %), respectively. Strain J2-1^T had chemotaxonomic properties resembling members of the genus Streptomyces. ll-Diaminopimelic acid, glucose and ribose were detected in the whole-cell hydrolysate. Diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositolmannoside, unidentified aminolipid and five unidentified phospholipids were detected as the polar lipids. The major cellular fatty acids were C_16 : 0 iso, C_15 : 0 anteiso, C_15 : 0 iso, C_16 : 0, C_17 : 0 anteiso, C_14 : 0 iso and C_17 : 0 iso. Strain J2-2^T a showed similar cell composition to members of the genus Kineosporia. Both isomers of ll- and meso-diaminopimelic acid were detected in the peptidoglycan. Arabinose, galactose, madurose and xylose were observed in the whole-cell hydrolysate. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, phosphatidylinositol mannoside, phosphatidylcholine, an unidentified phospholipid and an unidentified glycolipid. The major cellular fatty acids were C_16 : 0, C_18 : 1 ω9c, C_18 : 0 10-methyl, tuberculostearic acid, C_18 : 0 and C_17 : 0. Both strains could be distinguished from their closely related type strains according to their phenotypic characteristics. Comparative genome analysis indicated the delineation of two novel species based on digital DNA-DNA hybridization and average nucleotide identity values, which were below 70 and 95 %, respectively. The names proposed are Streptomyces corallincola sp. nov. (J2-1^T=TBRC 13503^T=NBRC 115066^T) and Kineosporia corallincola sp. nov. (J2-2^T=TBRC 13504^T=NBRC 114885^T).

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.

Anticancer activities, structure-activity relationship, and mechanism of action of 12-, 14-, and 16-membered macrolactones

Cancer remains one of the major causes of death worldwide despite the encouraging breakthroughs in the discovery of novel chemotherapeutic agents in recent years. The development of new effective anticancer candidates still represents a challenging endeavor due to the severe anticancer demands and the emergence of drug-resistant, especially multidrug-resistant, cancers. Macrolactones could regulate multiple signaling pathways in cancer cells and demonstrated potential anticancer effects, including inhibition of proliferation, metastasis, and angiogenic activity. Accordingly, macrolactones possess excellent efficacy against both drug-sensitive and drug-resistant cancer cells, and the rational design of macrolactones may provide valuable therapeutic interventions for cancers. The purpose of this review is as follows: (1) outline the recent advances made in the development of 12-, 14-, and 16-membered macrolactones with anticancer potential; (2) summarize the structure-activity relationship; and (3) discuss their anticancer mechanisms.

Structure Determination, Biosynthetic Origin, and Total Synthesis of Akazaoxime, an Enteromycin-Class Metabolite from a Marine-Derived Actinomycete of the Genus Micromonospora

A new enteromycin-class antibiotic, akazaoxime (1), possessing an aldoxime functionality in place of O-methyl nitronic acid, was isolated from the cultured extract of a marine-derived actinomycete of the genus Micromonospora, along with known A-76356 (2). The structure of 1, including the absolute stereochemistry of three chiral centers, was established by comprehensive analysis of nuclear magnetic resonance (NMR) and mass spectrometry data coupled with magnetic anisotropy analysis of its phenylglycine methyl ester derivatives. The stereochemistry of 2, not determined previously, was proven to be the same as that of 1 on the basis of the similarity of their NMR and specific rotation data. Precursor feeding experiments using ¹³C-labeled compounds elucidated that the carbon skeletons of 1 and 2 are constructed from propionate (methylmalonate), leucine, and glycine. Establishment of the concise and flexible synthetic route to 1 enabled us to implement biological evaluation of 1 and its unnatural analogues, demonstrating weak to moderate antimicrobial activities of 1 against Gram-positive Kocuria rhizophila [minimum inhibitory concentration (MIC) of 50 μg/mL] and those of synthetic analogues against a plant pathogen Glomerella cingulata (MIC of 50 μg/mL) and a human pathogen Trichophyton rubrum (MIC of 25-50 μg/mL).

TMKS8A, an antibacterial and cytotoxic chlorinated α-lapachone, from a sea slug-derived actinomycete of the genus Streptomyces

TMKS8A (1), a new chlorinated α-lapachone derivative, along with five known related metabolites, A80915 C (2), SF2415B1 (3), chlorinated dihydroquinone 3 (4), SF2415B3 (5), and A80915 C (6), were identified from the culture extract of Streptomyces sp. TMKS8, which was isolated from a sea slug, Paromoionchis tumidus. The structure of 1 was determined by the analysis of NMR and MS spectral data, assisted by NMR chemical shift prediction using DFT-based calculation. The absolute configuration was determined to be R by comparison of experimental and calculated ECD spectra. Compound 1 displayed antimicrobial activity against Gram-positive bacteria with MIC values ranging from 6.25 to 12.5 μg ml^-1 and cytotoxicity against murine leukemia P388 cells with IC₅₀ 9.8 μM.