13-Deoxytetrodecamycin, a new tetronate ring-containing antibiotic that is active against multidrug-resistant Staphylococcus aureus

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.

Characterization and partial purification of an antibacterial agent from halophilic actinomycetes Kocuria sp. strain rsk4

Introduction: The inevitable rise of antibiotic-resistant bacteria is a global health problem. These pathogens erode the utility of available antibiotics. Staphylococcus aureus is one of the major causes of community-acquired infections. The aim of work was to evaluate the marine actinomycetes for production of the antibacterial agent against pathogens.

Methods: Halophilic actinomycetes were isolated, characterized and screened for production of antibacterial agent against pathogenic bacteria. The antibacterial compounds were extracted by solvent extraction and separated by TLC based bioautography. Antibacterial compound was further purified by flash chromatography followed by high-performance liquid chromatography (HPLC) techniques. The active fraction was characterized by spectroscopy techniques. The minimum inhibitory concentration of antibiotic was determined against pathogens.

Results: A new halophilic actinomycetes strain rsk4 was isolated from marine water. It was designated as Kocuria sp. based on the physiological, biochemical and 16S rDNA sequencebased characters. It was able to produce broad-spectrum antibacterial compound and exhibited significant inhibitory activities against antibiotic-resistant S. aureus. The antibacterial compound was secreted optimally at 5% NaCl and neutral pH in the starch casein medium during stationary phase. The crude ethyl acetate extract was separated by chloroform-methanol, 24:1, v/v having Rf value 0.45. Bioassay of HPLC fractions confirms the presence of antibiotics picks at retention time: 3.24 minutes. The UV-Visible and mass spectra of the compound revealed that the active compound was different from other known antibiotics. The lowest minimum inhibitory concentration was recorded against S. aureus (30 µg/mL).

Conclusion: The result suggests that a broad-spectrum antibacterial compound obtained from halophilic actinomycetes is effective against pathogenic bacteria. This compound may be a good alternative treatment against antibiotic-resistant pathogen S. aureus.

A live bacteria SERS platform for the in situ monitoring of nitric oxide release from a single MRSA

A live bacteria SERS platform is developed for the precise and sensitive monitoring of nitric oxide release from a single MRSA.

Actinomycetes: still a source of novel antibiotics

Covering: 2006 to 2017Actinomycetes have been, for decades, one of the most important sources for the discovery of new antibiotics with an important number of drugs and analogs successfully introduced in the market and still used today in clinical practice. The intensive antibacterial discovery effort that generated the large number of highly potent broad-spectrum antibiotics, has seen a dramatic decline in the large pharma industry in the last two decades resulting in a lack of new classes of antibiotics with novel mechanisms of action reaching the clinic. Whereas the decline in the number of new chemical scaffolds and the rediscovery problem of old known molecules has become a hurdle for industrial natural products discovery programs, new actinomycetes compounds and leads have continued to be discovered and developed to the preclinical stages. Actinomycetes are still one of the most important sources of chemical diversity and a reservoir to mine for novel structures that is requiring the integration of diverse disciplines. These can range from novel strategies to isolate species previously not cultivated, innovative whole cell screening approaches and on-site analytical detection and dereplication tools for novel compounds, to in silico biosynthetic predictions from whole gene sequences and novel engineered heterologous expression, that have inspired the isolation of new NPs and shown their potential application in the discovery of novel antibiotics. This review will address the discovery of antibiotics from actinomycetes from two different perspectives including: (1) an update of the most important antibiotics that have only reached the clinical development in the recent years despite their early discovery, and (2) an overview of the most recent classes of antibiotics described from 2006 to 2017 in the framework of the different strategies employed to untap novel compounds previously overlooked with traditional approaches.

Genomics-Inspired Discovery of Three Antibacterial Active Metabolites, Aurantinins B, C, and D from Compost-Associated Bacillus subtilis fmb60

Fmb60 is a wild-type Bacillus subtilis isolated from compost with significant broad-spectrum antimicrobial activities. Two novel PKS clusters were recognized in the genome sequence of fmb60, and then three polyene antibiotics, aurantinins B, C, and D, 1-3, were obtained by bioactivity-guided isolation from the fermentation of fmb60. The structures of aurantinins B-D were elucidated by LC-HRMS and NMR data analysis. Aurantinins C and D were identified as new antimicrobial compounds. The three aurantinins showed significant activity against multidrug-resistant Staphylococcus aureus and Clostridium sporogenes. However, aurantinins B-D did not exhibit any cytotoxicity (IC50 > 100 μg/mL) against LO2 and Caco2 cell lines by MTT assay. Furthermore, using S. aureus as a model bacterium to explore the antibacterial mechanism of aurantinins B-D, it was revealed that the bactericidal activity of aurantinins B-D was related to their ability to disrupt the cell membrane.

Biosynthetic Genes for the Tetrodecamycin Antibiotics

We recently described 13-deoxytetrodecamycin, a new member of the tetrodecamycin family of antibiotics. A defining feature of these molecules is the presence of a five-membered lactone called a tetronate ring. By sequencing the genome of a producer strain, Streptomyces sp. strain WAC04657, and searching for a gene previously implicated in tetronate ring formation, we identified the biosynthetic genes responsible for producing 13-deoxytetrodecamycin (the ted genes). Using the ted cluster in WAC04657 as a reference, we found related clusters in three other organisms: Streptomyces atroolivaceus ATCC 19725, Streptomyces globisporus NRRL B-2293, and Streptomyces sp. strain LaPpAH-202. Comparing the four clusters allowed us to identify the cluster boundaries. Genetic manipulation of the cluster confirmed the involvement of the ted genes in 13-deoxytetrodecamycin biosynthesis and revealed several additional molecules produced through the ted biosynthetic pathway, including tetrodecamycin, dihydrotetrodecamycin, and another, W5.9, a novel molecule. Comparison of the bioactivities of these four molecules suggests that they may act through the covalent modification of their target(s).

IMPORTANCE

The tetrodecamycins are a distinct subgroup of the tetronate family of secondary metabolites. Little is known about their biosynthesis or mechanisms of action, making them an attractive subject for investigation. In this paper we present the biosynthetic gene cluster for 13-deoxytetrodecamycin in Streptomyces sp. strain WAC04657. We identify related clusters in several other organisms and show that they produce related molecules.