A total of 377 actinomycetes were isolated from eight soil samples collected from the Phatup Cave Forest Park and Phanangkhoi cave in northern Thailand. One hundred and sixty eight isolates (44.56%) were non-streptomycete based on their spore formations and isomeric forms of diaminopimelic acid. Among these, 50 isolates belong to the genus Micromonospora due to their characteristic single spore formation. Eleven randomly selected isolates of these rare actinomycetes were identified by using phenotypic data combined with 16S rDNA sequence-based phylogenetic analysis. Very rare genera such as Spirillospora, Catellatospora and Nonomuraea were also found. This is the first recorded isolation of Spirillospora and Nonomuraea from a cave soil. Phylogenetic analysis of 16S rRNA gene sequence data revealed that 5 of 11 randomly selected isolates might represent a new species. Two of them showed anti Gram-positive bacteria and anti-cancer activity. Caves are attractive places to look for new actinomycete species that might be a source of novel bioactive compounds.

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Semi-quantitative data and the identity or mass spectroscopic data are reported for 120 volatile metabolites from 26 selected Streptomyces isolates grown on suitable media. Approximately half of the metabolites are terpene derivatives.

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Desferrioxamine B (desferal^®) is the only therapeutic agent for chronic iron overload and acute iron intoxication. Therefore, new drug candidates are required for more effective treatments. Recent genome analyses of microorganisms have enabled us to identify cryptic gene clusters of secondary metabolism. In a genomic analysis of Streptomyces avermitilis, we found the putative biosynthetic gene cluster for nocardamin and desferrioxamine derivatives, the production of which by S. avermitilis had been unknown. To determine the synthesis of nocardamin and discover new derivatives in S. avermitilis, we performed a comprehensive analysis and isolation of secondary metabolites of S. avermitilis. We obtained nocardamin and its related compounds, including a derivative that initially was isolated as a microbial product. The biosynthetic pathway of nocardamin and the substrate specificity of its biosynthesis enzymes were proposed based on the structures of the isolated nocardamin derivatives. The production of nocardamin by S. avermitilis was completely suppressed by the addition of more than 5 μM ferric ions. An iron-dependent regulatory protein (IdeR)-binding motif was located upstream of the sidABCD operon, using the profile hidden Markov model method. To determine the regulation of nocardamin synthesis by IdeR in S. avermitilis, we constructed ideR deletion mutants. The production of nocardamin by the deletion mutants was not suppressed by ferric ions (up to 100 μM).

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A Gram-positive bacterium, designated strain Kis4-19^T, was isolated from the intestinal tract of a fish, and its taxonomic position was investigated by a polyphasic approach. The cells of strain Kis4-19^T were coccus-shaped, non-motile and non-sporulating. The peptidoglycan type of this organism was A3γ; LL-diaminopimeric acid (LL-A₂pm) was the diagnostic diamino acid of the peptidoglycan. The predominant menaquinone was MK-8(H₄), and the major fatty acids were iso-C_15:0, iso-C_14:0 and iso-C_16:0. Galactose was detected as a cell-wall sugar. The polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and lyso-phosphatidylethanolamine. The DNA G+C content was 71.1 mol%. Sequencing analysis of the 16S rRNA gene indicated that strain Kis4-19^T was closely related to Arsenicicoccus bolidensis CCUG 47306^T (97.5%). However, DNA–DNA hybridization results and phenotypic characteristics revealed that the strain Kis4-19^T differed from A. bolidensis. Therefore, strain Kis4-19^T represents a novel species of the genus Arsenicicoccus, for which the name Arsenicicoccus piscis sp. nov. is proposed. The type strain is Kis4-19^T (=NBRC 105830^T =DSM 22760^T).

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The nucleoside antibiotic A-500359s are produced by Streptomyces griseus SANK 60196. During a screening program of A-500359s high-producing strains, several interesting mutants were isolated and classified into three groups according to two characteristics, spore-forming ability and the retention of a giant linear plasmid SGF180, as follows: [spore+ SGF180-], [bald SGF180+] and [bald SGF180-]. A-500359s production was markedly decreased in all the mutants [spore+ SGF180-] and completely lacking in all the bald-type mutants. To understand the regulatory mechanisms of A-500359s production in these mutants, co-cultivation analyses were conducted in several mutant combinations, and the effect of an addition of an EtOAc extract, which was prepared from a culture broth of an A-500359s producer, was tested. A-500359s production was clearly restored when mutant [spore+ SGF180-] was co-cultivated with mutant [bald SGF180+] and the A-500359s production of the mutant [bald SGF180+] was activated by the addition of an EtOAc extract. The results suggested that SGF180 plays an important role in A-500359s production and that A-500359s biosynthesis might be controlled by a low molecular weight compound, such as an A-factor-like compound, synthesized by the product of afsA gene that was lost in all the tested bald-type mutants.

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Nucleocidin, a fairly broad antibacterial and trypanocidal agent produced by Streptomyces calvus, has the unique structure of 4′-α-fluoro-5′-O-sulfamoyl adenosine. This nucleoside antibiotic has been a target for organic synthesis in past decades; however, microbial large-scale production has not been established due to low yield and poor reproducibility. To activate the dormant secondary metabolism of S. calvus, we examined the effect of an rpoB mutation that was induced by ultraviolet light irradiation. The resulting rifampicin-resistant strains showed remarkably improved antibiotic activity, which was extracted by n-butanol and identified by Electron-Spray-Ionization Mass Spectrometry. DNA sequencing identified double mutations, C1309A and C1318A, in the rpoB gene (according to the numbering of Streptomyces coelicolor rpoB). The resulting amino acid substitutions, H437N and R440S, corresponded to two of the previously reported amino acid substitutions that allowed the activation of dormant actinorhodin production in S. lividans 66.

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