A novel actinomycete strain was isolated from sandy soil collected in Bangladesh. The culture formed pseudosporangia on short sporangiophores directly above the surface of the substrate mycelium. The pseudosporangia developed singly or in clusters and each pseudosporangium contained many non-motile oval to reniform spores with a smooth surface. The strain 3-54(41)^T contained meso-diaminopimelic acid in the cell wall, predominant menaquinone MK-9(H₆), and galactose, mannose, xylose and arabinose in the whole-cell hydrolysate. The diagnostic phospholipid was phosphatidylethanolamine, and branched iso-C_16:0 (44.0%), iso-C_14:0 (13.0%) and unsaturated C_18:1 (ω9c) (12.0%) were detected as the major cellular fatty acids. The acyl type of the peptidoglycan was glycolyl, and mycolic acids were not detected. The G+C content of the DNA was 71 mol%. The chemotaxonomic data indicate that this strain belongs to the family Micromonosporaceae. Phylogenetic analysis based on 16S rDNA sequence data also suggested that the strain 3-54(41)^T falls within this family. On the basis of phylogenetic analysis and the characteristic patterns of signature nucleotides as well as the morphological and chemotaxonomic data, our isolate is proposed to be Krasilnikovia gen. nov., and this strain should be classified as the species Krasilnikovia cinnamonea sp. nov. in the family Micromonosporaceae. The type strain is 3-54(41)^T (=JCM 13252^T = MTCC 8094^T).

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The taxonomic status of five actinomycete strains, 3-28(8)^T, 4-20(13), 3D-70(20), 5-81(36) and 3D-72(35)^T, isolated from sandy soil was studied using the polyphasic approach. All isolates produced branching substrate mycelia and developed spherical spore vesicles on aerial hyphae containing non-motile spores. They contained meso-diaminopimelic acid and the N-acetyl type of peptidoglycan. The predominant menaquinones were MK-9(H₄) and MK-9(H₆). Madurose, mannose, ribose, galactose and glucose were detected in the whole-cell hydrolysate. The diagnostic phospholipids were phosphatidylethanolamine and ninhydrin-positive phosphoglycolipids, and iso-C_16:0 and 10 methyl C_17:0 were detected as the major cellular fatty acids. These morphological and chemotaxonomic data were related to those of the genus Streptosporangium in the family Streptosporangiaceae. Phylogenetic analysis based on 16S rDNA sequence data suggested that the strains belong to the family Streptosporangiaceae, but not to any known genus, and form a monophyletic clade with Streptosporangium viridialbum and “Streptosporangium cinnabarinum”. The signature nucleotides of the members of this clade are different from those of any known genera of the family Streptosporangiaceae. On the basis of phylogenetic analysis and the characteristic patterns of signature nucleotides as well as the morphological and chemotaxonomic data, the genus Sphaerosporangium gen. nov. is proposed for our five isolates and the type strains of Streptosporangium viridialbum and “Streptosporangium cinnabarinum”. DNA–DNA hybridization and phenotypic characterization indicate that the new genus comprises four species, Sphaerosporangium melleum sp. nov. with the type strain 3-28(8)^T (=JCM 13064^T =DSM 44954^T), Sphaerosporangium rubeum sp. nov. with the type strain 3D-72(35)^T (=JCM 13067^T =DSM 44936^T), Sphaerosporangium cinnabarinum sp. nov. (=JCM 3291 =DSM 44094) and Sphaerosporangium viridialbum comb. nov. (=JCM 3027^T =DSM 43801^T).

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A short coccoid- or rod-shaped, non-motile actinomycete strain RC825^T was isolated from lichen in Izu-Oshima Island, Japan. A polyphasic study was undertaken to establish the taxonomic position of this strain. Phylogenetic analysis based on 16S rRNA gene sequence revealed that strain RC825^T forms an evolutionary lineage within the radiation of the genus Nocardioides. In particular, it forms a coherent cluster with Nocardioides oleivorans and Nocardioides ganghwensis with high sequence similarity of 98 and 97.5%, respectively. However, DNA–DNA hybridization experiment demonstrated that strain RC825^T is distinct from its closest phylogenetic neighbors, N. oleivorans and N. ganghwensis, with 44 and 39% relatedness, respectively. The cell-wall peptidoglycan of strain RC825^T contained LL-diaminopimelic acid, indicating wall chemotype I. The predominant menaquinone was MK-8(H₄). Strain RC825^T had a cellular fatty acid profile containing straight-chain, branched, unsaturated and 10-methyl fatty acids, and the major fatty acid was iso-C_16:0. The DNA G+C content of the strain was 74 mol%. On the basis of both phenotypic and phylogenetic evidence, the strain is separated from previously described Nocardioides species, and should be assigned to represent a novel species of the genus Nocardioides, for which the name Nocardioides exalbidus sp. nov. is proposed. The type strain is strain RC825^T (=IAM 15416^T=CCTCC AA206016^T).

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Actinomycetes, which produced antibacterial substances against Gram-positive bacteria in the presence of seawater only, were isolated from marine environment and characterized. Of the 100 isolates from Otsuchi Bay in Iwate, 41 failed to produce any antibacterial substances in the absence of seawater. However, of the 41, two were found to produce antibacterial substances in the presence of seawater. Strain No. 18 exhibited higher activity than strain No. 28 and was, therefore, selected for further studies. Phylogenetic analysis and physiological characterization showed a high similarity between strain No. 18 and Micromonospora globosa. However, M. globosa JCM 3126 did not produce any antibiotics in the presence of seawater. Therefore, the effect of seawater on the growth of strain No. 18 and its production of antibacterial substances was investigated. Strain No. 18 grew in a medium prepared with artificial seawater at a concentration range of 0–140% (v/v). The optimal concentration of growth ranged from 10 to 30% (v/v). However, production of antibacterial substances was observed in the concentration range 60–110% (v/v) despite poor growth. Thus, the production of antibacterial substances is seawater-dependent. The purification and characterization of the substances is now in progress.

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An investigation was conducted to explore the effect of the phytohormone indole-3-acetic acid (IAA) on cellular differentiation in streptomycetes. A total of 21 Streptomyces strains known to produce antibiotics were tested. IAA (1–20 μg/ml) in Bennett’s agar markedly stimulated aerial mycelium formation and antibiotic production in 12 and 13 test strains, respectively. The stimulating effect of IAA was confirmed even in a submerged culture: production of an anthracycline group antibiotic, rhodomycin, by S. purpurascens NBRC 13077 cultured in oatmeal-MYM broth, was markedly enhanced by addition of IAA (20 μg/ml). mRNA differential display (RT-PCR) analysis revealed that expression of rdmA, rdmB, rdmC, rdmD and rdmE, all genes involved in rhodomycin production, was up-regulated by IAA treatment in S. purpurascens. These results suggest that IAA may act as a common regulating agent for sporulation and secondary metabolism in streptomycetes.

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Hydroxycitric acid (HCA) is the principal acid produced by the tropical and subtropical plants Garcinia cambogia and Hibiscus subdariffa. The stereochemistry and biological activities of HCA have been well studied because it is used as a food additive and dietary supplement. Here we review current knowledge on the structure, biological occurrence, physiological activities and microbial production of HCA. Since stereoselective organic synthesis is difficult, and the habitat of the source plants is restricted, the availability of HCA is limited. Hence, we screened microorganisms to supply an alternative source and identified a species of Streptomyces that produces trace amounts of the Hibiscus-type HCA enantiomer. Subsequently, genome shuffling was applied to improve HCA production by the strain. Finally, we obtained improved strains that produce five times more HCA than the parent strain. In combination with a selective screening system, genome shuffling can be used to rapidly improve the production of secondary metabolites by Streptomyces species. Furthermore, genome-wide studies could be used to identify various critical mutations and provide new insights into the cellular regulation of the secondary metabolism of Streptomyces in the near future.

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