Guanahanolide A, a Meroterpenoid with a Sesterterpene Skeleton from Coral-Derived Streptomyces sp

New Insights on Biological Activities, Chemical Compositions, and Classifications of Marine Actinomycetes Antifouling Agents

Biofouling is the assemblage of undesirable biological materials and macro-organisms (barnacles, mussels, etc.) on submerged surfaces, which has unfavorable impacts on the economy and maritime environments. Recently, research efforts have focused on isolating natural, eco-friendly antifouling agents to counteract the toxicities of synthetic antifouling agents. Marine actinomycetes produce a multitude of active metabolites, some of which acquire antifouling properties. These antifouling compounds have chemical structures that fall under the terpenoids, polyketides, furanones, and alkaloids chemical groups. These compounds demonstrate eminent antimicrobial vigor associated with antiquorum sensing and antibiofilm potentialities against both Gram-positive and -negative bacteria. They have also constrained larval settlements and the acetylcholinesterase enzyme, suggesting a strong anti-macrofouling activity. Despite their promising in vitro and in vivo biological activities, scaled-up production of natural antifouling agents retrieved from marine actinomycetes remains inapplicable and challenging. This might be attributed to their relatively low yield, the unreliability of in vitro tests, and the need for optimization before scaled-up manufacturing. This review will focus on some of the most recent marine actinomycete-derived antifouling agents, featuring their biological activities and chemical varieties after providing a quick overview of the disadvantages of fouling and commercially available synthetic antifouling agents. It will also offer different prospects of optimizations and analysis to scale up their industrial manufacturing for potential usage as antifouling coatings and antimicrobial and therapeutic agents.

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 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).

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.

Tetrodecadazinone, a novel tetrodecamycin-pyridazinone hybrid with anti-liver fibrosis activity from Streptomyces sp. HU051

Tetrodecadazinone (1), a novel tetrodecamycin-pyridazinone hybrid possessing a new 1,2-dimethyl-1-(2-methylnonyl)decahydronaphthalene skeleton, and 4-hydroxydihydrotetrodecamycin (2) were separated from a culture of Streptomyces sp. HU051, together with a known compound, dihydrotetrodecamycin (3). Diverse spectroscopic approaches were applied to assign the structures of 1-3, and the structure of 1 was further confirmed by single crystal X-ray diffraction analysis. Compound 1 is the first example of a pyridazinone-containing natural product. Biosynthetically, 1 is proposed to be derived from a Michael addition reaction of a PKS-derived tetrodecamycin and a piperazic-acid-derived pyridazinone. Biological evaluation revealed 1 could reduce the expressions of extracellular matrix proteins (fibronectin and collagen I) and α-smooth muscle actin (α-SMA) in transforming growth factor-β (TGF-β1)-activated LX-2 cells. Preliminary mechanism study showed 1 exerted its anti-liver fibrosis effect by regulating TGF-β1/Smad2/3 signaling pathway.

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.

Structure-based molecular networking for the target discovery of novel germicidin derivatives from the sponge-associated streptomyces sp. 18A01

Four new α-pyrone derivatives, named germicidins P-S (1-4) along with nine known analogues (5-13) were discovered from the sponge-associated Streptomyces sp. 18A01 guided by Global Natural Products Social (GNPS) molecular networking, the LC-DAD-MS profile, and hexokinase II (HK2) inhibitory activity. The structures of 1-13 were elucidated by analysis of their HRMS, optical rotation, and NMR spectroscopic data. The absolute configurations of germicidin P (1) and germicidin Q (2) were determined on the basis of comparisons of experimental and theoretically calculated ECD spectra. Bioactivities of the isolated compounds were assayed against human HK2. The bioassay results showed that compounds 1-4 and 11-13 exhibited significant inhibitory activities against HK2, with IC₅₀ values ranging from 5.1 to 11.0 μM. A molecular docking simulation demonstrated that these germicidins were docked in the inner active site tunnel of HK2. Interestingly, the amino residue Arg91 has a better binding affinity and efficacy than the amino residue Asn89 in the process of HK2 binding to the ligands, resulting in better hexokinase inhibitory activity. This result provided a valuable perspective for better understanding their HK2 inhibition activity.

Chemistry, biosynthesis and biological activity of terpenoids and meroterpenoids in bacteria and fungi isolated from different marine habitats

The marine environment with its vast biological diversity encompasses many organisms that produce bioactive natural products. Marine microorganisms are rich sources of compounds from many structural classes with a multitude of biological activities. The biosynthesis of microbial natural products depends on a variety of biotic and abiotic factors in the marine environment, including temperature, nutrients, salinity and interaction with other microorganisms. Terpenoids, as one of the most important groups of natural products in terrestrial microorganisms are important metabolites for marine microorganisms. Here, we have reviewed the chemistry, biosynthesis and pharmacological activities of terpenoids, extracted from marine microbes, and then survey their potential applications in drug development. We also discussed the different habitats in which marine microorganisms are found including sediments, the flora, such as seaweeds, sea grasses, and mangroves as well as the fauna like sponges and corals. Amongst these habitats, marine sediments are the major source for terpenoids producing microorganisms. The marine bacteria produce mostly meroterpenoids, while the fungi are well known for production of isoprenoids. Interestingly, marine-derived microbial terpenoids have some structural characteristics such as halogenation, which are catalyzed by specific enzymes with distinct substrate specificity. These compounds have anticancer, antibacterial, antifungal, antimalarial and anti-inflammatory properties. The information collected here might provide useful clues for developing new medications.