Five new epothilone metabolites from Sorangium cellulosum strain So0157-2

Whole genome analysis of Streptomyces sp. RerS4, a Rehmannia glutinosa rhizosphere microbe producing a new lipopeptide

Rehmannia glutinosa, a valuable medicinal plant, is threatened by ring rot, a condition that greatly affects its yield and quality. Interactions between plant and the rhizosphere soil microbiome in the context of pathogen invasion are generally more specific, with recruitment of specialized microbes potentially antagonistic to a certain pathogen. Isolation of microorganisms from rhizosphere soil of healthy and ring rot-infected R. glutinosa was carried out to screen antifungal microbes. A strain designated RerS4 isolated from ring rot-infected R. glutinosa rhizosphere soil with strong antifungal activities was selected for further study. RerS4 was taxonomically characterized as the genus Streptomyces according to its morphology and 16S rRNA sequences that were most closely related to Streptomyces racemochromogenes NRRL B-5430T (99.72%) and Streptomyces polychromogenes NBRC 13072T (99.72%). A new lipopeptide isolated from RerS4 showed restrained proliferation, but was devoid of significant antibacterial and antioxidant activity with minimum inhibitory concentration (MIC) values of 20.3 ± 2.5 and 70.8 ± 3.7 μg/mL and half-maximal inhibitory concentration (IC50) values of 23.3 ± 0.8 and 58.8 ± 2.9 μg/mL, respectively. In addition, we report the complete genome sequence of Streptomyces sp. RerS4, which consists of a 7,301,482 bp linear chromosome and a 242,139 bp plasmid. Genome analysis revealed that Streptomyces sp. RerS4 contained 25 biosynthetic gene clusters (BGCs) for secondary metabolites, among which 68% had low similarities with known BGCs, leading us to believe that Streptomyces sp. RerS4 could produce valuable bioactive compounds.

Discovery of Three 22-Membered Macrolides by Deciphering the Streamlined Genome of Mangrove-Derived Streptomyces sp. HM190

Strain HM190, a moderate halophile, was isolated from rhizosphere soil of the mangrove Kandelia obovata in Fugong village, China. The 16S ribosomal RNA (rRNA) gene sequence and the results of phylogenetic analysis revealed that strain HM190 belonged to the genus Streptomyces and had the highest sequence similarity of 99.79% to Streptomyces heilongjiangensis NEAU-W2^T. The complete genome of strain HM190 comprised 7,762,826 bp in a linear chromosome with 71.97% G + C content. According to antiSMASH analysis, a total of 30 biosynthetic gene clusters (BGCs) were predicted to be involved in secondary metabolism, 12 of which were responsible for the production of polyketide- and non-ribosomal peptide-derived secondary metabolites. Gene cluster 5 was responsible for macrolide biosynthesis in a strain-specific 126,331-bp genomic island belonging to the left-arm region. Combined genomics–metabolomics analysis led to the discovery of three 22-membered macrolides (compounds 1–3). Their structures were elucidated by using spectroscopic techniques including high-resolution electrospray ionization mass spectroscopy (HRESIMS) and nuclear magnetic resonance (NMR). The absolute configurations of compounds 1–3 were determined by the X-ray single crystal diffraction and NMR data analysis. All three compounds displayed moderate cytotoxic activities toward tumor cell lines HepG2, A549, and HCT116.

Two new threonine-containing metabolites from fungus Curvularia inaequalis strain HS-FG-257

Two new threonine-containing metabolites, N-[4-hydroxy-3-prenyl-benzoyl]-L-threonine (1) and N-[2,2-dimethyl-2H-chromene-6-carbonyl]-L-threonine (2), were isolated from the fermentation broth of the soil fungus Curvularia inaequalis strain HS-FG-257. Their structures were elucidated through the interpretation of HR-ESIMS and extensive NMR spectroscopic data. Both compounds exhibited no cytotoxic activity against the test cell lines A549 and HCT-116.

Taxonomic Characterization and Secondary Metabolite Analysis of NEAU-wh3-1: An Embleya Strain with Antitumor and Antibacterial Activity

Cancer is a serious threat to human health. With the increasing resistance to known drugs, it is still urgent to find new drugs or pro-drugs with anti-tumor effects. Natural products produced by microorganisms have played an important role in the history of drug discovery, particularly in the anticancer and anti-infective areas. The plant rhizosphere ecosystem is a rich resource for the discovery of actinomycetes with potential applications in pharmaceutical science, especially Streptomyces. We screened Streptomyces-like strains from the rhizosphere soil of wheat (Triticum aestivum L.) in Hebei province, China, and thirty-nine strains were obtained. Among them, the extracts of 14 isolates inhibited the growth of colon tumor cell line HCT-116. Strain NEAU-wh-3-1 exhibited better inhibitory activity, and its active ingredients were further studied. Then, 16S rRNA gene sequence similarity studies showed that strain NEAU-wh3-1 with high sequence similarities to Embleya scabrispora DSM 41855T (99.65%), Embleya hyalina MB891-A1T (99.45%), and Streptomyces lasii 5H-CA11T (98.62%). Moreover, multilocus sequence analysis based on the five other house-keeping genes (atpD, gyrB, rpoB, recA, and trpB) and polyphasic taxonomic approach comprising chemotaxonomic, phylogenetic, morphological, and physiological characterization indicated that the isolate should be assigned to the genus Embleya and was different from its closely related strains, therefore, it is proposed that strain NEAU-wh3-1 may be classified as representatives of a novel species of the genus Embleya. Furthermore, active substances in the fermentation broth of strain NEAU-wh-3-1 were isolated by bioassay-guided analysis and identified by nuclear magnetic resonance (NMR) and mass spectrometry (MS) analyses. Consequently, one new Zincophorin analogue together with seven known compounds was detected. The new compound showed highest antitumor activity against three human cell lines with the 50% inhibition (IC50) values of 8.8-11.6 μg/mL and good antibacterial activity against four pathogenic bacteria, the other known compounds also exhibit certain biological activity.

Micromonospora zhangzhouensis sp. nov., a Novel Actinobacterium Isolated from Mangrove Soil, Exerts a Cytotoxic Activity in vitro

A new bacterial strain, designated HM134^T, was isolated from a sample of soil collected from a Chinese mangrove Avicennia marina forest. Assessed by a polyphasic approach, the taxonomy of strain HM134^T was found to be associated with a range of phylogenetic and chemotaxonomic properties consistent with the genus Micromonospora. Phylogenetic analysis based on the 16s rRNA gene sequence indicated that strain HM134^T formed a distinct lineage with the most closely related species, including M. rifamycinica AM105^T, M. wenchangensis CCTCC AA 2012002^T and M. mangrovi 2803GPT1-18^T. The ANI values between strain HM134^T and the reference strains ranged from 82.6% to 95.2%, which was below the standard criteria for classifying strains as the same species (96.5%). Strain HM134^T and related species shared in silico dDDH similarities values below the recommended 70% cut-off for the delineation of species (range from 25.7–62.6%). The DNA G+C content of strain HM134^T was 73.2 mol%. Analysis of phylogenetic, genomic, phenotypic and chemotaxonomic characteristics revealed that strain HM134^T is considered to represent a novel species of the genus Micromonospora, for which the name M. zhangzhouensis sp. nov. is proposed. The extract of strain HM134^T was demonstrated to exhibit cytotoxic activity against the human cancer cell lines HepG2, HCT-116 and A549. Active substance presented in the fermentation broth of strain HM134^T was isolated by bioassay-guided analysis and purified afterwards. A new derivative of diterpenoid was identified through electrospray ionizing mass spectrometry (MS) and nuclear magnetic resonance (NMR). The compound showed different cytotoxic activities against cancer cells, with the highest cytotoxicity against HCT-116, corresponding to IC₅₀ value of 38.4 μg/mL.

Two new compounds from Streptomyces sp. HS-NF-813

Two new derivatives of cytotoxic substance BE-52211, designed as BE-52211D (1) and BE-52211E (2), were isolated from the fermentation broth of the strain Streptomyces sp. HS-NF-813. Their structures were determined by 1D and 2D NMR techniques, ESI-MS and comparison with data from the literature. The absolute stereochemistry of 1 was elucidated by NMR data of the Mosher ester derivatives. Compounds 1 and 2 showed moderate cytotoxic activity against three human tumor cell lines.

Three New Isoflavonoid Glycosides from the Mangrove-Derived Actinomycete Micromonospora aurantiaca 110B

The mangrove ecosystem is a rich resource for the discovery of actinomycetes with potential applications in pharmaceutical science. Besides the genus Streptomyces, Micromonospora is also a source of new bioactive agents. We screened Micromonospora from the rhizosphere soil of mangrove plants in Fujian province, China, and 51 strains were obtained. Among them, the extracts of 12 isolates inhibited the growth of human lung carcinoma A549 cells. Strain 110B exhibited better cytotoxic activity, and its bioactive constituents were investigated. Consequently, three new isoflavonoid glycosides, daidzein-4'-(2-deoxy-α-l-fucopyranoside) (1), daidzein-7-(2-deoxy-α-l-fucopyranoside) (2), and daidzein-4',7-di-(2-deoxy-α-l-fucopyranoside) (3) were isolated from the fermentation broth of strain 110B. The structures of the new compounds were determined by spectroscopic methods, including 1D and 2D nuclear magnetic resonance (NMR) and high-resolution electrospray ionization mass spectrometry (HR-ESIMS). The result of medium-changing experiments implicated that these new compounds were microbial biotransformation products of strain M. aurantiaca 110B. The three compounds displayed moderate cytotoxic activity to the human lung carcinoma cell line A549, hepatocellular liver carcinoma cell line HepG2, and the human colon tumor cell line HCT116, whereas none of them showed antifungal or antibacterial activities.

Two new glutarimide antibiotics from Streptomyces sp. HS-NF-780

Two new glutarimide antibiotics, 9-methylstreptimidone 2-α-D-glucopyranoside (1), and hydroxyiso-9-methylstreptimidone (2), along with a known compound, 9-methylstreptimidone (3), have been isolated from the broth of Streptomyces sp. HS-NF-780. Their structures were determined on the basis of spectroscopic analysis, including 1D and 2D NMR techniques as well as ESI-MS and comparison with data from the literature. By modified Mosher's method and acid hydrolysis, the absolute configurations of compounds 1 and 2 were established. Compounds 1 and 2 exhibited moderate cytotoxic activity.

A new anthracycline-type metabolite from Streptomyces sp. NEAU-L3

A new anthracycline-type metabolite, designated as tetracenoquinocin A (1), was isolated from the fermentation broth of Streptomyces sp. NEAU-L3. Its structure was determined on the basis of spectroscopic analysis, including 1D and 2D NMR techniques as well as ESI-MS and comparison with data from the literature. Compound 1 showed potent cytotoxic activity against three cancer cell lines (HepG2, A549, HCT-116) with IC₅₀ values of 5.57, 24.30 and 20.82 μM, respectively.

Isolation and characterisation of the epothilone gene cluster with flanks from high alkalotolerant strain Sorangium cellulosum (So0157-2)

Epothilones are cytotoxic macrolactones having auspicious anti-tumorous activities, but merely produced by rare Sorangium strains. Here, we have focused on the epothilone gene cluster from special niche bacterial strain, S. cellulosum So0157-2. Therefore, we have isolated a high pH tolerant S. cellulosum strain So0157-2 and characterized the epothilones gene cluster and its flanks by cosmid/fosmid libraries preparation and sequencing. The assembly spanned 94,459 bp and consisted of 56,019 bp core region. Remarkably, the core as well as upstream 420 bp and downstream 315 bp were highly conserved, while further neighboring regions varied extremely. Transposase traces were identified near the core of clusters, supporting that the transposon-mediated transgenesis is a naturally evolved strategy for the cluster's dissemination. A predicted neighboring esterase gene was identified as a potential epothilone-resistance gene preventing self-toxicity. Novel modification or regulatory genes, a multi-position-cyclo releasing gene and their relationship with corresponding analogs were identified in strain So0157-2. These findings open the door to discover additional, naturally evolved epothilone-related genes for significant applications in industrial as well as clinical sector.

A new androstanoid metabolite from a soil fungus Curvularia borreriae strain HS-FG-237

A new androstanoid metabolite, 4α-methyl-9α-methoxyandrosta-8,15-diene-3,17-dione (1), was isolated from a soil fungus Curvularia borreriae (Pleosporaceae) strain HS-FG-237. Its structure was determined by extensive spectroscopic and X-ray diffraction analyses. Compound 1 exhibited poor cytotoxicity toward HCT-116 cells by CCK-8 assay and weak anti-inflammatory activity in an ANA-1 murine macrophages model.

A comprehensive review of glycosylated bacterial natural products

A systematic analysis of all naturally-occurring glycosylated bacterial secondary metabolites reported in the scientific literature up through early 2013 is presented. This comprehensive analysis of 15 940 bacterial natural products revealed 3426 glycosides containing 344 distinct appended carbohydrates and highlights a range of unique opportunities for future biosynthetic study and glycodiversification efforts.

Chromopeptide A, a highly cytotoxic depsipeptide from the marine sediment-derived bacterium Chromobacterium sp. HS-13-94

A bicyclic depsipeptide, chromopeptide A (1), was isolated from a deep-sea-derived bacterium Chromobacterium sp. HS-13-94. Its structure was determined by extensive spectroscopic analysis and by comparison with a related known compound. The absolute configuration of chromopeptide A was established by X-ray diffraction analysis employing graphite monochromated Mo K_α radiation (λ=0.71073 Å) with small Flack parameter 0.03. Chromopeptide A suppressed the proliferation of HL-60, K-562, and Ramos cells with average IC₅₀ values of 7.7, 7.0, and 16.5 nmol/L, respectively.

Activation of apoptotic pathway in normal, cancer ovarian cells by epothilone B

The epothilones, a new class of microtubule-targeting agents, seem to be a very promising alternative to the current strategy of cancer treatment. We have analyzed the aspects of epothilone B (Epo B) on cellular metabolism of tumor (OV-90) and normal (MM 14) ovarian cells. The observed effects were compared with those of paclitaxel (PTX), which is now a standard for the treatment of ovarian cancer. The results provide direct evidence that Epo B is considerably more cytotoxic to human OV-90 ovarian cancer cells than PTX. We have found, that antitumor efficacy of this new drug is related to its apoptosis-inducing ability, which was confirmed during measurements typical markers of the process. Epo B induced changes in morphology of cells, mitochondrial membrane potential and cytochrome c release. Also a slight increase of the intracellular calcium level was observed. Moreover, we have found that ROS production, stimulated by Epo B, is directly involved in the induction of apoptosis via mitochondrial pathway.

Two new metabolites from a soil fungus Curvularia affinis strain HS-FG-196

Two new metabolites, pyrenocine J (1) and pyrenochaetic acid D (2), together with two known metabolites, pyrenocine A (3) and pyrenochaetic acid A (4), were isolated from a soil fungus, Curvularia affinis strain HS-FG-196. Their structures were established by extensive spectroscopic analysis. Compound 1 showed cytotoxic activity against the human hepatic cancer cell line HepG2 with an IC(50) value of 28.5 μg/ml.

Glycosylation and production characteristics of epothilones in alkali-tolerant Sorangium cellulosum strain So0157-2

3-O-alpha-D-ribofuranosyl epothilone A (epothiloneoside A) is a major component of glycosylated epothilones in Sorangium cellulosum strain So0157-2. The production and glycosylation ratios of epothiloneoside A in both solid and liquid culture conditions with various pH values and carbon sources were studied. The results showed that glycosylation occurs whenever epothilones are produced, regardless of changes in pH values, production time curves, and different carbon sources. We suggest that glycosylation is a stable process, paralleling the biosynthesis of epothilones in the So0157-2 strain.

Using chemobiosynthesis and synthetic mini-polyketide synthases to produce pharmaceutical intermediates in Escherichia coli

Recombinant microbial whole-cell biocatalysis is a valuable approach for producing enantiomerically pure intermediates for the synthesis of complex molecules. Here, we describe a method to produce polyketide intermediates possessing multiple stereogenic centers by combining chemobiosynthesis and engineered mini-polyketide synthases (PKSs). Chemobiosynthesis allows the introduction of unnatural moieties, while a library of synthetic bimodular PKSs expressed from codon-optimized genes permits the introduction of a variety of ketide units. To validate the approach, intermediates for the synthesis of trans-9,10-dehydroepothilone D were generated. The designer molecules obtained have the potential to greatly reduce the manufacturing cost of epothilone analogues, thus facilitating their commercial development as therapeutic agents.