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In our large-scale search for antimicrobial-producing bacteria, we isolated an actinomycete strain from rhizospheric soil of Bambusa vulgaris. The strain designated BP-8 showed noticeable antibacterial activity. BP-8 was subjected to a whole-genome analysis via a polyphasic taxonomy approach, and its antibacterial metabolite was identified by HRLS-MS. The results of the physiological and morphological analyses indicated that BP-8 is an aerobic, neutrophilic, mesophilic organism that is tolerant to 8% NaCl and can use a wide range of carbohydrates. It forms curly sporophores with a warty surface. The results of the phylogenetic and average nucleotide identity analyses and in silico DNA–DNA hybridization calculation indicated that BP-8 represents the type strain of a novel Streptomyces species. A comparative in silico analysis of the genome sequences of BP-8 and its closest related strains revealed the presence of genes encoding chemotaxonomic markers characteristic of Streptomyces. The antibacterial compound was identified as amicetin. Genomic mining also revealed more than 10 biosynthetic gene clusters that have not been described previously and may lead to the discovery of new valuable compounds. On the basis of these results, strain BP-8T (=VKM Ac-3066T = CCTCC AA 2024094T) is proposed as the type strain of the novel species Streptomyces sirii sp. nov.

Five new nucleoside antibiotics, named streptcytosines A–E (1–5), and six known compounds, de-amosaminyl-cytosamine (6), plicacetin (7), bamicetin (8), amicetin (9), collismycin B (10), and SF2738 C (11), were isolated from a culture broth of Streptomyces sp. TPU1236A collected in Okinawa, Japan. The structures of new compounds were elucidated on the basis of their spectroscopic data (HRFABMS, IR, UV, and 2D NMR experiments including 1H-1H COSY, HMQC, HMBC, and NOESY spectra). Streptcytosine A (1) belonged to the amicetin group antibiotics, and streptcytosines B–E (2–5) were derivatives of de-amosaminyl-cytosamine (6), 2,3,6-trideoxyglucopyranosyl cytosine. Compound 1 inhibited the growth of Mycobacterium smegmatis (MIC = 32 µg/mL), while compounds 2–5 were not active at 50 µg/disc. Bamicetin (8) and amicetin (9) showed the MICs of 16 and 8 µg/mL, respectively.

The interaction of a highly conserved secondary structural RNA motif of Halobacterium halobium and Escherichia coli 23S ribosomal RNAs with the peptidyl transferase inhibitor antibiotic amicetin has been investigated by proton NMR spectroscopy and molecular modelling. The NMR spectra of the synthetic 35mer RNA motifs revealed spectral features characteristic of a stable, well folded A-RNA type tertiary conformation, including resolved resonances assigned to unpaired bases located in the middle of the motif strongly implicated in amicetin binding. Addition of amicetin to the 35mer RNA samples was accompanied by significant and discrete changes to the spectra which can be qualitatively interpreted to the changes induced to the local conformation of the RNA motifs arising from the formation of a specific complex with amicetin. These results are also supported by the unconstrained molecular model of RNA-amicetin complex which highlights potential interactions between the two molecular components.