Kitamycins, new antimycin antibiotics produced by Streptomyces sp

Microbiological Aspects of Unique, Rare, and Unusual Fatty Acids Derived from Natural Amides and Their Pharmacological Profile

In the proposed review, the pharmacological profile of unique, rare, and unusual fatty acids derived from natural amides is considered. These amides are produced by various microorganisms, lichens, and fungi. The biological activity of some natural fatty acid amides has been determined by their isolation from natural sources, but the biological activity of fatty acids has not been practically studied. According to QSAR data, the biological activity of fatty acids is shown, which demonstrated strong antifungal, antibacterial, antiviral, antineoplastic, anti-inflammatory activities. Moreover, some fatty acids have shown rare activities such as antidiabetic, anti-infective, anti-eczematic, antimutagenic, and anti-psoriatic activities. For some fatty acids that have pronounced biological properties, 3D graphs are shown that show a graphical representation of unique activities. These data are undoubtedly of both theoretical and practical interest for chemists, pharmacologists, as well as for the pharmaceutical industry, which is engaged in the synthesis of biologically active drugs.

A new secondary metabolite from the fermented mycelia of Streptomyces antibiotic H41-55

An actinomycete strain, H41-55 from sea sediment was identified as Streptomyces antibiotic on the basis of its morphological, physiological and biochemical characteristics as well as 16S rDNA data. A new secondary metabolite, (2S,3R)-N-[3-(formylamino)-2-hydroxybenzoyl]-l-threonine propyl ester (1), together with five known compounds was isolated from fermentation product by use of silica gel and Sephadex LH-20 column chromatography, and preparative RP-C18 HPLC, and identified by HR-TOF-MS and NMR spectra. The cytotoxicities of these isolates against three cancer cell lines and their antifungal activities on Candida albicans were tested. Compounds 1, 3, 5, and 6 displayed moderate cytotoxicity. 5 and 6 showed inhibitory activity on C. albicans.

Neoantimycins A and B, Two Unusual Benzamido Nine-Membered Dilactones from Marine-Derived Streptomyces antibioticus H12-15

An actinomycete strain (H12-15) isolated from a sea sediment in a mangrove district was identified as Streptomycesantibioticus on the basis of 16S rDNA gene sequence analysis as well as the investigation of its morphological, physiological, and biochemical characteristics. Two novel benzamido nonacyclic dilactones, namely neoantimycins A (1) and B (2), together with the known antimycins A_1ab (3a,b), A_2a (4), and A₉ (5), were isolated from the culture broth of this strain. Compounds 1 and 2 are the first natural modified ATNs with an unusual benzamide unit. The structures of these new compounds, including their absolute configuration, were established on the basis of HRMS, NMR spectroscopic data, and quantum chemical ECD calculations. Their cytotoxicities against human breast adenocarcinoma cell line MCF-7, the human glioblastoma cell line SF-268, and the human lung cancer cell line NCI-H460 were also tested. All compounds exhibited mild cytotoxic activity. However, Compounds 1 and 2 showed no activity against C. albicans at the test concentration of 1 mg/mL via paper disc diffusion, while the known antimycins showed obvious antifungal activity.

Kitamycin C, a new antimycin-type antibiotic from Streptomyces antibioticus strain 200-09

An actinomycete strain 200-09, isolated from a soil sample collected from the coast of Hawaii, USA, was identified as Streptomyces antibioticus on the basis of its morphological, physiological and biochemical characteristics as well as 16S rDNA analysis. A new antimycin-type antibiotic, kitamycin C (1), together with kitamycin A (2), kitamycin B (3), urauchmycin B (4), deisovaleryblastomycin (5) was isolated from a cultured broth of strain 200-09. The structure of the new compound was determined by spectroscopic data, including HR-ESI-MS and NMR. All the compounds exhibited antifungal activities against Candida albicans with MIC of about 25.0 μg mL^-1.

Taxonomy, Physiology, and Natural Products of Actinobacteria

Actinobacteria are Gram-positive bacteria with high G+C DNA content that constitute one of the largest bacterial phyla, and they are ubiquitously distributed in both aquatic and terrestrial ecosystems. Many Actinobacteria have a mycelial lifestyle and undergo complex morphological differentiation. They also have an extensive secondary metabolism and produce about two-thirds of all naturally derived antibiotics in current clinical use, as well as many anticancer, anthelmintic, and antifungal compounds. Consequently, these bacteria are of major importance for biotechnology, medicine, and agriculture. Actinobacteria play diverse roles in their associations with various higher organisms, since their members have adopted different lifestyles, and the phylum includes pathogens (notably, species of Corynebacterium, Mycobacterium, Nocardia, Propionibacterium, and Tropheryma), soil inhabitants (e.g., Micromonospora and Streptomyces species), plant commensals (e.g., Frankia spp.), and gastrointestinal commensals (Bifidobacterium spp.). Actinobacteria also play an important role as symbionts and as pathogens in plant-associated microbial communities. This review presents an update on the biology of this important bacterial phylum.

Antimycin-type depsipeptides: discovery, biosynthesis, chemical synthesis, and bioactivities

This review discusses the isolation, structural variation, biosynthesis, chemical synthesis, and biological activities of antimycin-type depsipeptides.

Biosynthesis of antimycins with a reconstituted 3-formamidosalicylate pharmacophore in Escherichia coli

Antimycins are a family of natural products generated from a hybrid nonribosomal peptide synthetase (NRPS)-polyketide synthase (PKS) assembly line. Although they possess an array of useful biological activities, their structural complexity makes chemical synthesis challenging, and their biosynthesis has thus far been dependent on slow-growing source organisms. Here, we reconstituted the biosynthesis of antimycins in Escherichia coli, a versatile host that is robust and easy to manipulate genetically. Along with Streptomyces genetic studies, the heterologous expression of different combinations of ant genes enabled us to systematically confirm the functions of the modification enzymes, AntHIJKL and AntO, in the biosynthesis of the 3-formamidosalicylate pharmacophore of antimycins. Our E. coli-based antimycin production system can not only be used to engineer the increased production of these bioactive compounds, but it also paves the way for the facile generation of novel and diverse antimycin analogues through combinatorial biosynthesis.

The regulation and biosynthesis of antimycins

Antimycins (>40 members) were discovered nearly 65 years ago but the discovery of the gene cluster encoding antimycin biosynthesis in 2011 has facilitated rapid progress in understanding the unusual biosynthetic pathway. Antimycin A is widely used as a piscicide in the catfish farming industry and also has potent killing activity against insects, nematodes and fungi. The mode of action of antimycins is to inhibit cytochrome c reductase in the electron transport chain and halt respiration. However, more recently, antimycin A has attracted attention as a potent and selective inhibitor of the mitochondrial anti-apoptotic proteins Bcl-2 and Bcl-x_L. Remarkably, this inhibition is independent of the main mode of action of antimycins such that an artificial derivative named 2-methoxyantimycin A inhibits Bcl-x_L but does not inhibit respiration. The Bcl-2/Bcl-x_L family of proteins are over-produced in cancer cells that are resistant to apoptosis-inducing chemotherapy agents, so antimycins have great potential as anticancer drugs used in combination with existing chemotherapeutics. Here we review what is known about antimycins, the regulation of the ant gene cluster and the unusual biosynthetic pathway.

Comprehensive investigation of marine Actinobacteria associated with the sponge Halichondria panicea

Representatives of Actinobacteria were isolated from the marine sponge Halichondria panicea collected from the Baltic Sea (Germany). For the first time, a comprehensive investigation was performed with regard to phylogenetic strain identification, secondary metabolite profiling, bioactivity determination, and genetic exploration of biosynthetic genes, especially concerning the relationships of the abundance of biosynthesis gene fragments to the number and diversity of produced secondary metabolites. All strains were phylogenetically identified by 16S rRNA gene sequence analyses and were found to belong to the genera Actinoalloteichus, Micrococcus, Micromonospora, Nocardiopsis, and Streptomyces. Secondary metabolite profiles of 46 actinobacterial strains were evaluated, 122 different substances were identified, and 88 so far unidentified compounds were detected. The extracts from most of the cultures showed biological activities. In addition, the presence of biosynthesis genes encoding polyketide synthases (PKSs) and nonribosomal peptide synthetases (NRPSs) in 30 strains was established. It was shown that strains in which either PKS or NRPS genes were identified produced a significantly higher number of metabolites and exhibited a larger number of unidentified, possibly new metabolites than other strains. Therefore, the presence of PKS and NRPS genes is a good indicator for the selection of strains to isolate new natural products.

Potent inhibitors of pro-inflammatory cytokine production produced by a marine-derived bacterium

Cytokines produced through the antigen presenting cell (APC)-T-cell interaction play a key role in the activation of the allergic asthmatic response. Evaluating small molecules that inhibit the production of these pro-inflammatory proteins is therefore important for the discovery of novel chemical structures with potential antiasthma activity. We adapted a mouse splenocyte cytokine assay to screen a library of 2,500 marine microbial extracts for their ability to inhibit T(H)2 cytokine release and identified potent activity in a marine-derived strain CNQ431, identified as a Streptomyces species. Bioactivity guided fractionation of the organic extract of this strain led to the isolation of ten new 9-membered bis-lactones, splenocins A-J (1-10). The new compounds display potent biological activities, comparable to that of the corticosteroid dexamethasone, with IC(50) values from 2 to 50 nM in the splenocyte cytokine assay. This study provides the foundation for the optimization of these potent anti-inflammatory compounds for development in the treatment of asthma.