A novel bone resorption inhibitor, A-75943 isolated from Streptomyces sp. SANK 61296

Production of secondary metabolites in stirred tank bioreactor co-cultures of Streptomyces noursei and Aspergillus terreus

The focus of the study was to characterize the bioprocess kinetics and secondary metabolites production in the novel microbial co-cultivation system involving Streptomyces noursei ATCC 11455 (the producer of an antifungal substance known as nystatin) and Aspergillus terreus ATCC 20542 (the source of lovastatin, a cholesterol-lowering drug). The investigated “A. terreus vs. S. noursei” stirred tank bioreactor co-cultures allowed for the concurrent development and observable biosynthetic activity of both species. In total, the production profiles of 50 secondary metabolites were monitored over the course of the study. The co-cultures were found to be effective in terms of enhancing the biosynthesis of several metabolic products, including mevinolinic acid, an acidic form of lovastatin. This work provided a methodological example of assessing the activity of a given strain in the co-culture by using the substrates which can be metabolized exclusively by this strain. Since S. noursei was shown to be incapable of lactose utilization, the observed changes in lactose levels were attributed to A. terreus and thus confirmed its viability. The study was complemented with the comparative microscopic observations of filamentous morphologies exhibited in the co-cultures and corresponding monocultures.

Stress-Driven Discovery of New Angucycline-Type Antibiotics from a Marine Streptomyces pratensis NA-ZhouS1

Natural products from marine actinomycetes remain an important resource for drug discovery, many of which are produced by the genus, Streptomyces. However, in standard laboratory conditions, specific gene clusters in microbes have long been considered silent or covert. Thus, various stress techniques activated latent gene clusters leading to isolation of potential metabolites. This study focused on the analysis of two new angucycline antibiotics isolated from the culture filtrate of a marine Streptomyces pratensis strain NA-ZhouS1, named, stremycin A (1) and B (2) which were further determined based on spectroscopic techniques such as high resolution time of flight mass spectrometry (HR-TOF-MS), 1D, and 2D nuclear magnetic resonance (NMR) experiments. In addition, four other known compounds, namely, 2-[2-(3,5-dimethyl-2-oxo-cyclohexyl)-6-oxo-tetrahydro-pyran-4yl]-acetamide (3), cyclo[l-(4-hydroxyprolinyl)-l-leucine] (4), 2-methyl-3H-quinazoline-4-one (5), and menthane derivative, 3-(hydroxymethyl)-6-isopropyl-10,12-dioxatricyclo[7.2.1.0]dodec-4-en-8-one (6) were obtained and elucidated by means of 1D NMR spectrometry. Herein, we describe the "Metal Stress Technique" applied in the discovery of angucyclines, a distinctive class of antibiotics that are commonly encoded in microbiomes but have never been reported in "Metal Stress" based discovery efforts. Novel antibiotics 1 and 2 exhibited antimicrobial activities against Pseudomonas aeruginosa, methicillin resistant Staphylococcus aureus (MRSA), Klebsiella pneumonia, and Escherichia coli with equal minimum inhibitory concentration (MIC) values of 16 µg/mL, while these antibiotics showed inhibition against Bacillus subtilis at MIC value of approximately 8⁻16 µg/mL, respectively. As a result, the outcome of this investigation revealed that metal stress is an effective technique in unlocking the biosynthetic potential and resulting production of novel antibiotics.

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.

A novel antibiotic produced by Streptomyces noursei Da07210

A novel antibiotic 210-A, named as (6S,8aS,9S,11S,12aR)-6-hydroxy-9,10-dimethyldecahydrobenzo[d]azecine-2,4,12(3H)-trione, was isolated from the fermentation broth of Streptomyces noursei Da07210, its structure was unambiguously established by spectral analyses and chemical comparison with related cycloheximide. Experiments demonstrated that 210-A bore strong activity against Fusarium oxysporum f. sp. cubense race four (Foc race four), which also showed antitumor activity against SMMC-7721 human hepatocarcinoma cells and S180 murine sarcoma, and the IC(50) values were 0.77 and 0.74 microg/ml, respectively.

Nontraditional microbial bioactive metabolites

Microorganisms produce low-molar-mass secondary metabolites exhibiting different biological activities, which are used. e.g., in medicine as antimicrobial and antifungal agents, alkaloids and toxins. Some of these substances have highly diverse biological activities and unusual structures. They are produced by streptomycetes, fungi, and bacilli, but interesting products have also been obtained from microorganisms growing in extreme conditions. Several thousands of microbial products have so far been discovered and many other, which can be potentially useful and/or prospective for human use, can still be in the offing.