Cycloimidamicins, Novel natural lead compounds for translation inhibition in Pseudomonas aeruginosa.

Pseudomonas aeruginosa is one of the most concerning pathogenic bacteria. We screened antibiotics using a highly drug-sensitive P. aeruginosa strain and an oligotrophic medium, and successfully isolated novel antibiotics, namely cycloimidamicins (CIMs), from a rare actinomycete strain, Lentzea sp. MM249-143F7. X-ray and nuclear magnetic resonance analyses revealed that CIMs possess a distinctive and unprecedented molecular structure, containing tetramic acid and an imidazole ring bound directly to indolone. The CIMs exhibited potent antibacterial activity against Gram-negative bacteria, as well as translation inhibition in Escherichia coli in both intact cells and in vitro. Additionally, E. coli strains resistant to known translation inhibitors did not exhibit cross-resistance to CIMs, suggesting that CIMs inhibit bacterial growth by blocking translation through a novel mechanism.

Isolation of new derivatives of the 20-membered macrodiolide bispolide from Kitasatospora sp. MG372-hF19.

New three macrocyclic diolides, named bispolides C-E (1-3), were isolated from a fermentation broth of the actinomycete strain MG372-hF19, which produces an indole glycoside and leptomycins as we reported previously. The absolute structures of compounds 1-3 were elucidated by NMR and X-ray crystallography. Compounds 1-3 diverge from the known nine bispolides in their different alkylation patterns on the 20-membered macrocyclic diolide skeleton and the side chain in their planar structures. Furthermore, compounds 1-3 exhibited antibacterial activity against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococci and cytotoxic activity against human cancer cell lines. Among them, compound 3 has the most potent biological activities against bacteria and tumor cells. Additionally, using a membrane-potential-sensitive fluorescence probe, we found that compounds 1-3 and elaiophylin have a similar effect on membrane potential in A549 human lung cancer cells.

Sealutomicins, new enediyne antibiotics from the deep-sea actinomycete Nonomuraea sp. MM565M-173N2.

A Nonomuraea sp. strain MM565M-173N2 was isolated from deep-sea sediment off the Sanriku coast, and new antibiotics were evaluated against carbapenem-resistant Enterobacteriaceae (CRE), which is a problematic group of bacteria because of their antimicrobial resistance. From 220 l of fermented broth from strain MM565M-173N2, we isolated four new antibiotics by gel filtration and HPLC, designated as sealutomicins A (1.8 mg), B (1.5 mg), C (0.8 mg), and D (0.8 mg). Their structures were determined from MS, NMR, and CD spectra. Sealutomicin A was found to be a new enediyne antibiotic, while sealutomicins B-D were aromatized products from sealutomicin A. Sealutomicin A showed strong antibacterial activity (MIC 0.05-0.2 µg ml-1) against CRE.