Polyphasic Identification of Rhizomonospora bruguierae gen. nov., sp. nov., Isolated from Mangrove Rhizosphere Soil

A novel yellowish-white actinobacterial strain, designated as TS60-4CT, was isolated from the rhizosphere soil of the mangrove Bruguiera gymnorhiza (L.) Lam. in Okinawa, Japan, and was subjected to a polyphasic assessment. The strain could grow at 0-3.0% NaCl concentrations (w/v), pH 6.0-10.0, and 20-37 °C. The 16S rRNA gene sequences-based phylogeny showed that the novel isolate belongs to the family Micromonosporaceae and that it shared the highest sequence similarity (98.4%) with Micromonospora craniellae LHW63014T. The hydrolysate of cell-wall of strain TS60-4CT contained alanine, glutamic acid, glycine, and meso-A2pm. The acyl type of muramic acid was N-glycolyl. The main (> 10%) fatty acids were anteiso-C17:0 (22.1%), iso-C16:0 (17.8%), iso-C15:0 (14.7%), and anteiso-C15:0 (10.3%) and the predominant menaquinones of the isolate were MK-9(H6) and MK-9(H4). The polar lipids of the isolate were phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol, an unidentified aminolipid, and three unidentified lipids. The genome size of strain TS60-4CT was 6.7 Mbp with a DNA G + C content of 72.4%. The average nucleotide identity, digital DNA-DNA hybridization, and average amino acid identity value could differentiate strain TS60-4CT from its closely related taxa. The genome of the strain had 22 putative biosynthetic gene clusters for secondary metabolites, indicating a significant potential as a producer of bioactive chemicals. Consequently, the strain is considered to represent a novel genus and a new species of the family Micromonosporaceae, for which the name Rhizomonospora bruguierae gen. nov., sp. nov. is proposed. The type species is R. bruguierae, with the type strain TS60-4CT (= NBRC 107566T = TBRC 2024T).

New antimalarial iromycin analogs produced by Streptomyces sp. RBL-0292

Two new antimalarial compounds, named prenylpyridones A (1) and B (2), were discovered from the actinomycete cultured material of Streptomyces sp. RBL-0292 isolated from the soil on Hamahiga Island in Okinawa prefecture. The structures of 1 and 2 were elucidated as new iromycin analogs having α-pyridone ring by MS and NMR analyses. Compounds 1 and 2 showed moderate in vitro antimalarial activity against chloroquine-sensitive and chloroquine-resistant Plasmodium falciparum strains, with IC50 values ranging from 80.7 to 106.7 µM.

Actinomycetospora termitidis sp. nov., an insect-derived actinomycete isolated from termite (Odontotermes formosanus)

Strain Odt1-22T, an insect-derived actinomycete was isolated from a termite (Odontotermes formosanus) that was collected from Chanthaburi province, Thailand. Strain Odt1-22T was aerobic, Gram-stain-positive, and produced bud-like spore chain on the substrate hypha. According to chemotaxonomic analysis, strain Odt1-22T contained meso-diaminopimelic acid in peptidoglycan and the whole-cell hydrolysates contained arabinose, galactose, glucose, and ribose. The major menaquinone was MK-8(H4). The diagnostic phospholipids were diphosphatidylglycerol, hydroxyphosphatidylethanolamine, phosphatidylethanolamine and phosphatidylglycerol. Phylogenetic analysis based on 16 S rRNA gene sequence revealed that strain Odt1-22T was identified to the genus Actinomycetospora and showed high similarity values with A. chiangmaiensis DSM 45062 T (99.24%), A. soli SF1T (99.24%) and A. corticicola 014-5 T (98.17%). The genomic size of strain Odt1-22T was 6.6 Mbp with 73.8% G + C content and 6355 coding sequences (CDSs). The genomic analysis, strain Odt1-22T and closely related species A. chiangmaiensis DSM 45062 T, A. soli SF1T and A. corticicola DSM 45772 T displayed the values of average nucleotide identity-blast (ANIb) at 83.7-84.1% and MUMmer (ANIm) at 86.6-87.0%. Moreover, the results of digital DNA-DNA hybridization values between strain Odt1-22T and related Actinomycetospora species were 45.8-50.5% that lower than the threshold value of commonly used to delineate separated species level. On the basis of phenotypic, chemotaxonomic, and genotypic data, strain Odt1-22T represented a novel species within the genus Actinomycetospora, for which the name Actinomycetospora termitidis sp. nov. is proposed. The type strain of the species is Odt1-22T (= TBRC 16192 T = NBRC 115965 T).

Binding Mode-Based Physicochemical Screening Method Using d-Ala-d-Ala Silica Gel and Chemical Modification Approach to Facilitate Discovery of New Macrolactams, Banglactams A and B, from Nonomuraea bangladeshensis K18-0086

Utilizing a binding mode-based physicochemical screening method using d-Ala-d-Ala silica gel, two new macrolactams, named banglactams A (1) and B (2), were discovered from the culture broth of Nonomuraea bangladeshensis K18-0086. In the course of our investigation, we found that d-Ala-d-Ala silica gel precisely differentiated the chemical structures of banglactams and separated them. However, we were not able to obtain enough of 1 to elucidate the structure due to its instability and insolubility. To overcome this challenge, we chemically modified 1 to improve solubility, enabling us to obtain a sufficient material supply for the indirect determination of the structure. Antibacterial activity evaluation of banglactams revealed that 1 binding to d-Ala-d-Ala silica gel exhibited antibacterial activity against Staphylococcus aureus; however, this was not the case with 2. This research indicates the utility of our original binding mode-based PC screening method, and the combination strategy of PC and chemical modifications led us to discover novel antibacterial compounds.

A new analog of dihydroxybenzoic acid from Saccharopolyspora sp. KR21-0001

Actinomycetes are well-known as the main producers of bioactive compounds such as antibiotics, anticancers, and immunosuppressants. Screening of natural products from actinomycetes has been an essential part of several drug discovery programs. Finding such novel biologically active metabolites is immensely important because of their beneficial health effects. Recently, the discovery of new compounds has diverted attention to rare actinomycetes, since they are rich sources of natural products. In this study, a collection of rare actinomycetes at Kitasato University has been screened for potential novel compound producers. Among the rare actinomycetes, Saccharopolyspora sp. KR21-0001 isolated from soil on Ōha Island, Okinawa, Japan was selected as a potential producer. The strain was cultured in 20 L of production medium in a jar fermenter and the culture broth was extracted. Further purification revealed the presence of a new compound designated KR21-0001A (1). The structure was elucidated by NMR, and the absolute stereochemistry was determined by advanced Marfey's method. The results indicated that 1 is a new analog of dihydroxybenzoic acid. 1 has no antimicrobial activity against bacteria and fungi but showed potent antioxidant activity.

Phytohabitans aurantiacus sp. nov., an actinomycete isolated from soil

A novel actinomycete, designated RD004123T, was isolated from a soil sample collected in Hokkaido, Japan, and its taxonomic position was investigated by a polyphasic approach. Phylogenetic analysis based on 16S rRNA gene sequence comparisons revealed that strain RD004123T fell within the cluster of the family Micromonosporaceae but did not form a reliable cluster with any member of the family. The similarity values between strain RD004123T and the type species of 29 genera in the family Micromonosporaceae were 91.7-97.7 %. Meanwhile, phylogenomic analyses indicated that strain RD004123T was closely related to members of the genus Phytohabitans. Strain RD004123T contained both meso-diaminopimelic acid and l-lysine as the diagnostic diamino acids of the peptidoglycan. The predominant isoprenoid quinones were MK-10(H8) and MK-10(H6), and the major fatty acids were anteiso-C17 :  0, iso-C16 :  0, iso-C15 :  0 and C17 :  0. The detected polar lipids were phosphatidylinositol mannosides, phosphatidylinositol, phosphatidylethanolamine and diphosphatidylglycerol. These chemotaxonomic features corresponded to those of the genus Phytohabitans. Meanwhile, the results of genome comparison analyses and phenotypic characterizations distinguished strain RD004123T from the other members of the genus Phytohabitans. Therefore, strain RD004123T should be assigned as representing a novel species of the genus Phytohabitans, for which the name Phytohabitans aurantiacus sp. nov. is proposed. The type strain is RD004123T (=NBRC 114997T=DSM 114330T).

Emblestatin: a new peptide antibiotic from Embleya scabrispora K20-0267

A new peptide, emblestatin (1), was discovered from a culture broth of Embleya scabrispora K20-0267. This strain was isolated from soil using an agar medium containing lysozyme. Based on NMR and mass spectrometric analyses, 1 consists of 2-(2-hydroxyphenyl)-2-oxazoline, β-alanine, glutamine, Nα-methyl-Nω-hydroxyornithine and 3-amino-1-hydroxy-2-piperidone moieties. Further analysis using the advanced Marfey's method revealed that all amino acids with the stereogenic α-carbon in 1 had the L configuration. Compound 1 exhibited iron chelating activity and weak antibacterial activity against Proteus vulgaris and Staphylococcus aureus.

Development of a drug discovery approach from microbes with a special focus on isolation sources and taxonomy

After the successful discoveries of numerous antibiotics from microorganisms, frequent reisolation of known compounds becomes an obstacle in further development of new drugs from natural products. Exploration of biological sources that can provide novel scaffolds is thus an urgent matter in drug lead screening. As an alternative source to the conventionally used soil microorganisms, we selected endophytic actinomycetes, marine actinomycetes, and actinomycetes in tropical areas for investigation and found an array of new bioactive compounds. Furthermore, based on the analysis of the distribution pattern of biosynthetic gene clusters in bacteria together with available genomic data, we speculated that biosynthetic gene clusters for secondary metabolites are specific to each genus. Based on this assumption, we investigated actinomycetal and marine bacterial genera from which no compounds have been reported, which led to the discovery of a variety of skeletally novel bioactive compounds. These findings suggest that consideration of environmental factor and taxonomic position is critically effective in the selection of potential strains producing structurally unique compounds.

Species-specific secondary metabolism by actinomycetes of the genus Phytohabitans and discovery of new pyranonaphthoquinones and isatin derivatives

To further exploit secondary metabolic potential of a minor actinomycete genus Phytohabitans within the family Micromonosporaceae, metabolite profiling by HPLC-UV analysis, combined with 16S rDNA sequence-based phylotyping were attempted on seven Phytohabitans strains available at the public culture collection. The strains were grouped into three clades and each exhibited unique and distinct metabolite profiles, which were highly conserved among strains within the same clade. These results were consistent with previous observations on two other actinomycetes genera, reconfirming species-specificity of secondary metabolite production, which were conventionally thought to be strain-specific. A strain RD003215, belonging to the P. suffuscus clade, produced multiple metabolites, some of which were presumed to be naphthoquinones. Liquid fermentation followed by chromatographic separation of the broth extract led to the discovery of three new pyranonaphthoquinones, designated habipyranoquinones A-C (1-3), and one new isatin derivative, (R)-N-methyl-3-hydroxy-5,6-dimethoxyoxindole (4), along with three known synthetic compounds, 6,8-dihydroxydehydro-α-lapachone (5), N-methyl-5,6-dimethoxyisatin (6), and 5,6-dimethoxyisatin (7). Structures of 1-4 were unequivocally elucidated by NMR, MS, and CD spectral analysis, with assistance of density functional theory-based NMR chemical shift prediction and ECD spectral calculation. Compound 2 displayed antibacterial activity against Kocuria rhizophila and Staphylococcus aureus with MIC 50 µg/mL and cytotoxicity against P388 murine leukemia cells with an IC₅₀ value of 34 µM. Compounds 1 and 4 also showed cytotoxicity against P388 cells with IC₅₀ values of 29 and 14 µM, respectively.

Bisprenyl naphthoquinone and chlorinated calcimycin congener bearing thiazole ring from an actinomycete of the genus Phytohabitans

A bisprenyl naphthoquinone, phytohabinone (1), and a calcimycin congener with unusual modifications, phytohabimicin (2), were isolated from the culture extract of Phytohabitans sp. RD003013. The structures of 1 and 2 were determined by NMR and MS analyses, and the absolute configuration of 2 was established by using electronic circular dichroism (ECD) calculation. The prenylation pattern of 1 was unprecedented among the known prenylated naphthoquinones. Compound 2 represents a spiroacetal core of polyketide origin substituted with a thiazole carboxylic acid and a dichrolopyrrole moiety, which is an unprecedented modification pattern in the known calcimycin family natural products. Remarkably, 2 showed moderate antimicrobial activity against a Gram-negative bacterium Ralstonia solanacearum while calcimycin was inactive. Additionally, 2 inhibits the migration of EC17 cancer cells at noncytotoxic concentrations.

Phytohabitols A-C, δ-Lactone-Terminated Polyketides from an Actinomycete of the Genus Phytohabitans

Phytohabitols A-C (1-3), new terminally δ-lactonized linear polyketides, were isolated from the culture extract of a rare actinomycete of the genus Phytohabitans. The structures of 1-3, substituted with multiple methyl and hydroxy groups on a conjugated and a skipped diene-containing backbone, were elucidated by NMR and MS spectroscopic analyses. The absolute configuration of 1 was determined by chemical derivatization and chiral anisotropic analysis, coupled with ROESY and J-based configuration analysis. In addition, closely similar 1H and 13C NMR data and optical rotations among 1-3 supported the same stereochemistry of these polyketides. The related streptomycetes metabolites lagunapyrones B, C, and D have α-pyrone rings on the linear part in place of the δ-lactone, but their chirality at the C19-C21 stereocenters were opposite from those described here, posing a question on the previous assignment made solely by comparison of the optical rotations of four possible diastereomers. Compounds 1-3 inhibited migration of cancer cells with IC50 values of 15, 11, and 8.3 μM, respectively, at noncytotoxic concentrations. In addition, 1-3 displayed potent antitrypanosomal activity against Trypanosoma cruzi with IC50 values of 12, 6.4, and 18 μM, comparable to a commonly used therapeutic drug, benznidazole (IC50 16 μM).

Polyketide Synthase and Nonribosomal Peptide Synthetase Gene Clusters in Type Strains of the Genus Phytohabitans

(1) Background: Phytohabitans is a recently established genus belonging to rare actinomycetes. It has been unclear if its members have the capacity to synthesize diverse secondary metabolites. Polyketide and nonribosomal peptide compounds are major secondary metabolites in actinomycetes and expected as a potential source for novel pharmaceuticals. (2) Methods: Whole genomes of Phytohabitans flavus NBRC 107702^T, Phytohabitans rumicis NBRC 108638^T, Phytohabitans houttuyneae NBRC 108639^T, and Phytohabitans suffuscus NBRC 105367^T were sequenced by PacBio. Polyketide synthase (PKS) and nonribosomal peptide synthetase (NRPS) gene clusters were bioinformatically analyzed in the genome sequences. (3) Results: These four strains harbored 10, 14, 18 and 14 PKS and NRPS gene clusters, respectively. Most of the gene clusters were annotated to synthesis unknown chemistries. (4) Conclusions: Members of the genus Phytohabitans are a possible source for novel and diverse polyketides and nonribosomal peptides.

Endophytic actinomycetes: promising source of novel bioactive compounds

Endophytic actinomycetes associated with plant roots are a relatively untapped source of potential new bioactive compounds. This is becoming increasingly important, as the returns from discovery research on soil-dwelling microbes, have been continuously diminishing. We have isolated more than 1000 strains of actinomycetes from plant roots in our search for novel bioactive compounds, identified and assayed their bioactive metabolites, as well as investigated their biosynthetic genes for generating secondary metabolites. This has resulted in the discovery of several interesting compounds. Creation of plant root clone libraries enabled us to confirm that we had, indeed, isolated endophytes. In this paper, we introduce our approach to this promising line of research, incorporating data from other publications, and illustrate the potential that endophytic actinomycetes offer as a new source of novel lead compounds.

Continuing fascination of exploration in natural substances from microorganisms†

In the search for novel organic compounds, I think it is of paramount importance not to overlook the pursuit of microorganism diversity and the abilities those microorganisms hold as a resource. In commemoration of Professor Satoshi Ōmura’s Nobel Prize in Physiology or Medicine, I will briefly describe the microorganism that produces avermectin and then discuss how innovating isolation methods and pioneering isolation sources have opened the door to numerous new microorganism resources. Furthermore, as exploratory research of substances views the world from many different angles—from biological activity to a compound’s physiochemical properties—it is possible to discover a novel compound from a well-known microorganism. Based on this, I will discuss the future prospects of exploratory research.

Search for new compounds from Kitasato microbial library by physicochemical screening

The Ōmura research group of the Kitasato Institute has isolated multiple microorganisms over a period of five decades. The resulting collection comprises a broad spectrum of microbes, including strains producing novel and diverse compounds with biological activities. A bioassay-guided fractionation of microbial culture broths has been employed to screen the microbial collection for compounds with new biological activities. And numerous novel natural products have been discovered among the microbial metabolites produced by members of the collection. However, dereplication of already known compounds and their potential analogs is a vital part of the discovery process of new microbial natural products. Recently, it has become easy to acquire the ultraviolet (UV) and mass spectrometry (MS) spectra of many single components of microbial culture broths in combination with high-performance liquid chromatography. To achieve most effective utilization of our microbial library, new compounds from microbial culture broths were investigated by employing an approach based on the physico-chemical properties using spectral analyses such as UV and MS and color reaction, collectively designated as physicochemical (PC) screening. As a result of physicochemical screening, many new compounds were identified among the secondary metabolites of fresh isolated rare actinomycetes and Streptomyces spp. preserved for a long time as producer of biological compounds. In this review, we introduce the Kitasato microbial library and the new compounds discovered from the library by PC screening.

Phytohabitans kaempferiae sp. nov., an endophytic actinomycete isolated from the leaf of Kaempferia larsenii

A novel endophytic actinomycete, designated strain KK1-3T, which formed single spores and long chains of spores (more than 10 spores) was isolated from surface-sterilized Kaempferia larsenii leaf collected from Ubon Ratchathani province, Thailand. The isolate contained l-lysine, meso-diaminopimelic acid and hydroxyl diaminopimelic acid in the cell-wall peptidoglycan. The whole-cell sugars included glucose, mannose, rhamnose, ribose, galactose and xylose. The characteristic phospholipids were phosphatidylethanolamine, phosphatidylmethylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylinositol and phosphoglycolipids. The predominant menaquinones were MK-10(H8), MK-10(H6) and MK-10(H4). The predominant cellular fatty acids were anteiso-C17 : 0 and iso-C16 : 0. The G+C content of the genomic DNA was 71 mol%. Phylogenetic analysis using 16S rRNA gene sequences revealed that strain KK1-3T should be classified as representing a member of the genus Phytohabitans. The similarity values of sequences between this strain and those of the closely related species, Phytohabitans houttuyneae K11-0057T (99.0 %), Phytohabitans suffuscus K07-0523T (98.9 %), Phytohabitans flavus K09-0627T (98.6 %) and Phytohabitans rumicisK11-0047T (98.1 %) were observed. The DNA-DNA hybridization result and some physiological and biochemical properties indicated that KK1-3T could be readily distinguished from its closest phylogenetic relatives. On the basis of these phenotypic and genotypic data, this strain represents a novel species, for which the name Phytohabitans kaempferiae sp. nov. is proposed. The type strain is strain KK1-3T (=BCC 66360T =NBRC 110005T).

Actinoplanes lichenis sp. nov., isolated from lichen

A novel species of the genus Actinoplanes, strain LDG1-22T, for which we propose the name Actinoplanes lichenis sp. nov., was isolated from a lichen sample collected from tree bark in Thailand. The taxonomic position of the species has been described based on a polyphasic approach. Strain LDG1-22T produced irregular sporangia on agar media. It contained meso-diaminopimelic acid in the cell-wall peptidoglycan. The major menaquinone was MK-9(H4); the polar lipids were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannosides and phosphatidylglycerol. Whole-cell hydrolysates contained ribose, glucose, mannose and small amounts of arabinose and xylose. The major cellular fatty acids were anteiso-C15 : 0 (31.2 %) and iso-C16 : 0 (14.2 %). Mycolic acids were absent. The G+C content was 73.6 %. 16S rRNA gene sequence analysis of strain LDG1-22T showed highest similarity (98.8 %) to Actinoplanes friuliensis DSM 45797T and it clustered with Actinoplanes nipponensis JCM 3264T and Actinoplanes missouriensis JCM 3121T in phylogenetic tree analysis. On the basis of the phenotypic characteristics and DNA-DNA relatedness, strain LDG1-22T could be distinguished from related species of the genus Actinoplanes and so represents a novel species of this genus. The type strain of Actinoplanes lichenis sp. nov. is LDG1-22T ( = JCM 30485T = TISTR 2343T = PCU 344T).

Biotechnological application and taxonomical distribution of plant growth promoting actinobacteria

Plant growth promoting (PGP) bacteria are involved in various interactions known to affect plant fitness and soil quality, thereby increasing the productivity of agriculture and stability of soil. Although the potential of actinobacteria in antibiotic production is well-investigated, their capacity to enhance plant growth is not fully surveyed. Due to the following justifications, PGP actinobacteria (PGPA) can be considered as a more promising taxonomical group of PGP bacteria: (1) high numbers of actinobacteria per gram of soil and their filamentous nature, (2) genome dedicated to the secondary metabolite production (~5 to 10 %) is distinctively more than that of other bacteria and (3) number of plant growth promoter genera reported from actinobacteria is 1.3 times higher than that of other bacteria. Mechanisms by which PGPA contribute to the plant growth by association are: (a) enhancing nutrients availability, (b) regulation of plant metabolism, (c) decreasing environmental stress, (d) control of phytopathogens and (e) improvement of soil texture. Taxonomical and chemical diversity of PGPA and their biotechnological application along with their associated challenges are summarized in this paper.

Rhizocola hellebori gen. nov., sp. nov., an actinomycete of the family Micromonosporaceae containing 3,4-dihydroxydiaminopimelic acid in the cell-wall peptidoglycan

An actinomycete strain, K12-0602T, was isolated from the root of a Helleborus orientalis plant in Japan. The 16S rRNA gene sequence of strain K12-0602T showed that it had a close relationship with members of the family Micromonosporaceae and the 16S rRNA gene sequence similarity values between strain K12-0602T and type strains of type species of 27 genera belonging to the family Micromonosporaceae were below 96.2 %. MK-9 (H4) and MK-9 (H6) were detected as major menaquinones, and galactose, xylose, mannose and ribose were present in the whole-cell hydrolysate. The acyl type of the peptidoglycan was glycolyl. Major fatty acids were iso-C15 : 0, iso-C16 : 0, C17 : 1ω9c and anteiso-C17 : 0. Phosphatidylethanolamine was detected as the phospholipid corresponding to phospholipid type II. The G+C content of the genomic DNA was 67 mol%. Analyses of the cell-wall peptidoglycan by TLC and LC/MS showed that it was composed of alanine, glycine, hydroxylglutamic acid and an unknown amino acid, which was subsequently determined to be 3,4-dihydroxydiaminopimelic acid using instrumental analyses, including NMR and mass spectrometry. On the basis of the phylogenetic analysis and chemotaxonomic characteristics, strain K12-0602T represents a novel species of a new genus in the family Micromonosporaceae , for which the name Rhizocola hellebori gen. nov., sp. nov. is proposed. The type strain of the type species is K12-0602T ( = NBRC 109834T = DSM 45988T). This is the first report, to our knowledge, of 3,4-dihydroxydiaminopimelic acid being found as a diamino acid in bacterial cell-wall peptidoglycan.

Streptomyces siamensis sp. nov., and Streptomyces similanensis sp. nov., isolated from Thai soils

Three actinomycete strains, KC-038(T), KC-031 and KC-106(T), were isolated from soil samples collected in the southern Thailand. The morphological and chemotaxonomic properties of strains KC-038(T), KC-031 and KC-106(T) were consistent with the characteristics of members of the genus Streptomyces, that is, the formation of aerial mycelia bearing spiral spore chains; the presence of LL-diaminopimelic acid in the cell wall, MK-9 (H6), MK-9 (H4) and MK-9 (H8) as the predominant menaquinones; and C16:0, iso-C16:0 and anteiso-C15:0 as the major cellular fatty acids. 16S rRNA gene sequence analyses indicated that strains KC-038(T) and KC-031 were highly similar (99.9%), and they were closely related to S. olivochromogenes NBRC 3178(T) (98.1%) and S. psammoticus NBRC 13971(T) (98.1%). Strain KC-106(T) was closely related to S. seoulensis NBRC 16668(T) (98.9%), S. recifensis NBRC 12813(T) (98.9%), S. chartreusis NBRC 12753(T) (98.7%) and S. griseoluteus NBRC 13375(T) (98.4%). The values of DNA-DNA relatedness between the isolates and the type strains of the related species were below 70%. On the basis of the polyphasic evidence, the isolates should be classified as two novel species, namely Streptomyces siamensis sp. nov. (type strain, KC-038(T) = NBRC 108799(T) = PCU 328(T) = TISTR 2107(T)) and Streptomyces similanensis sp. nov. (type strain, KC-106(T) = NBRC 108798(T) = PCU 329(T) = TISTR 2104(T)).

Trehangelins A, B and C, novel photo-oxidative hemolysis inhibitors produced by an endophytic actinomycete, Polymorphospora rubra K07-0510

Three new natural products, designated trehangelins A, B and C, were isolated by solvent extraction, silica gel and octadecylsilyl silica gel column chromatographies and subsequent preparative HPLC from the cultured broth of an endophytic actinomycete strain, Polymorphospora rubra K07-0510. The trehangelins consisted of a trehalose moiety and two angelic acid moieties. Trehangelins A (IC50 value, 0.1 mg ml(-1)) and C (IC50 value, 0.4 mg ml(-1)), with symmetric structures, showed potent inhibitory activity against hemolysis of red blood cells induced by light-activated pheophorbide a. However, trehangelin B, with an asymmetric structure, displayed only a slight inhibition (IC50 value, 1.0 mg ml(-1)).

Wangella harbinensis gen. nov., sp. nov., a new member of the family Micromonosporaceae

A novel endophytic actinomycete, designated strain NEAU-J3(T), was isolated from soybean root (Glycine max (L.) Merr) and characterized using a polyphasic approach. Phylogenetic analysis based on 16S rRNA gene sequences suggested that strain NEAU-J3(T) fell within the family Micromonosporaceae. The strain was observed to form an extensively branched substrate mycelium, which carried non-motile oval spores with a smooth surface. The cell walls of strain NEAU-J3(T) were determined to contain meso-diaminopimelic acid and galactose, ribose and glucose were detected as whole-cell sugars. The major menaquinones were determined to be MK-9(H(4)) and MK-9(H(6)). The phospholipids detected were phosphatidylcholine and phosphatidylethanolamine. The major cellular fatty acids were determined to be C(16:0), C(18:1) ω9c, C(18:0), C(17:0), C(17:1) ω7c, anteiso-C(17:0), C(16:1) ω7c and C(15:0). The DNA G + C content was 62.5 mol%. On the basis of the morphological and chemotaxonomic characteristics, phylogenetic analysis and characteristic patterns of 16S rRNA gene signature nucleotides, strain NEAU-J3(T) is considered to represent a novel species of a new genus within the family Micromonosporaceae, for which the name Wangella harbinensis gen. nov., sp. nov. is proposed. The type strain of Wangella harbinensis is strain NEAU-J3(T) (=CGMCC 4.7039(T) = DSM 45747(T)).

Phytohabitans flavus sp. nov., Phytohabitans rumicis sp. nov. and Phytohabitans houttuyneae sp. nov., isolated from plant roots, and emended description of the genus Phytohabitans

An actinomycete strain, designated K09-0627T, was isolated from the roots of an orchid collected in Okinawa Prefecture, Japan. Two actinomycete strains K11-0047T and K11-0057T were isolated from the roots of Rumex acetosa and Houttuynia cordata collected in Kanagawa Prefecture, Japan. 16S rRNA gene sequence analyses indicated that the isolates belonged to the genus Phytohabitans, and that they were closely related to each other and to Phytohabitans suffuscus K07-0523T. The DNA–DNA relatedness values between the three isolates and Phytohabitans suffuscus were below 70 %. On the basis of phylogenetic analysis, DNA–DNA relatedness values and phenotypic characteristics, the strains should be classified as novel species in the genus Phytohabitans , for which the names Phytohabitans flavus sp. nov. (type strain, K09-0627T = JCM 17387T = NBRC 107702T = DSM 45551T), Phytohabitans rumicis sp. nov. (type strain, K11-0047T = JCM 17829T = NBRC 108638T = BCC 48146T) and Phytohabitans houttuyneae sp. nov. (type strain, K11-0057T = JCM 17830T = NBRC 108639T = BCC 48147T) are proposed.

Xiangella phaseoli gen. nov., sp. nov., a member of the family Micromonosporaceae

A novel endophytic actinomycete, designated strain NEAU-J5(T) was isolated from roots of snap bean (Phaseolus vulgaris L.). Comparative analysis of the 16S rRNA gene sequence indicated that NEAU-J5(T) is phylogenetically related to members of the family Micromonosporaceae. The whole-cell sugars were galactose, mannose and glucose. The predominant menaquinones were MK-9(H4) and MK-9(H6). The major fatty acids were C16:0, C18:0, C17:1ω7c, iso-C15:0 and C17:0. The phospholipids were phosphatidylmethylethanolamine, phosphatidylethanolamine, phosphatidylcholine, phosphatidylinositol and phosphatidylinositol mannoside. The DNA G+C content was 72.2 mol%. On the basis of the morphological and chemotaxonomic characteristics, phylogenetic analysis and characteristic patterns of 16S rRNA gene signature nucleotides, strain NEAU-J5(T) represents a novel species of a new genus within the family Micromonosporaceae, for which the name Xiangella phaseoli gen. nov., sp. nov. is proposed. The type strain of Xiangella phaseoli is strain NEAU-J5(T) (=CGMCC 4.7038(T)=DSM 45730(T)).

Diversity and isolation of rare actinomycetes: an overview

A renewed interest in the development of new antimicrobial agents is urgently needed to combat the increasing number of antibiotic-resistant strains of pathogenic microorganisms. Actinomycetes continue to be the mainstream supplier of antibiotics used in industry. The likelihood of discovering a new compound with novel chemical structure can be increased with intensive efforts in isolating and screening of rare genera of microorganisms to include in natural-product-screening collections. An unexpected variety of rare actinomycetes is now being isolated worldwide from previously uninvestigated diverse natural habitats, using different selective isolation methods. These isolation efforts include methods to enhance growth (enrichment) of rare actinomycetes, and eliminate unwanted microorganisms (pretreatment). To speed up the strain isolation process, knowledge about the distribution of such unexploited groups of microorganisms must also be augmented. This is a summary of using these microorganisms as new potential biological resources, and a review of almost all of the selective isolation methods, including pretreatment and enrichment techniques that have been developed to date for the isolation of rare actinomycetes.

Isolation of actinomycetes from the root of the plant, Ophiopogon japonicus, and proposal of two new species, Actinoallomurus liliacearum sp. nov. and Actinoallomurus vinaceus sp. nov

Actinomycete strains K10-0485(T) and K10-0528(T) were isolated from the roots of Ophiopogon japonicus collected in Yokohama, Kanagawa Prefecture, Japan. The 16S ribosomal RNA (rRNA) gene sequences, morphological characteristics and chemotaxonomic data indicated that these strains belonged to the genus Actinoallomurus. Strain K10-0485(T) showed high similarity of the 16S rRNA gene sequence with A. luridus TT02-15(T) (99.1%), but the DNA-DNA hybridization relatedness values between strain K10-0485(T) and A. luridus TT02-15(T) were below 70%. Three species showed similarities of 16S rRNA gene sequences with K10-0528(T), namely A. spadix JCM 3146(T) (98.0%), A. purpureus TTN02-30(T) (98.0%) and A. luridus TT02-15(T) (97.9%), but all similarity values of the 16S rRNA gene sequences were lower than the boundary value (98.7%) for distinguishing as different species. Based on phylogenetic analyses, DNA-DNA hybridization relatedness and physiological characteristics, the two isolated strains should be classified as two new species in the genus Actinoallomurus, and we propose the names Actinoallomurus liliacearum sp. nov. and Actinoallomurus vinaceus sp. nov. The type strain of Actinoallomurus liliacearum is K10-0485(T) (=JCM 17938(T), BCC 49424(T), NBRC 108672(T)) and that of Actinoallomurus vinaceus is K10-0528(T) (=JCM 17939(T), BCC 49425(T), NBRC 108763(T)).

Actinoallomurus radicium sp. nov., isolated from the roots of two plant species

Three strains, K08-0182T, K08-0178 and K08-0195 were isolated from the paste of ground plant roots collected in Kanagawa Prefecture, Japan. These strains contained meso-diaminopimelic acid and lysine as the diamino acids in cell-wall peptidoglycan, and MK-9(H6) and MK-9(H8) as the predominant menaquinones. The G+C contents of the DNA were 72–73 mol%. Taken together, these characteristics combined with 16S rRNA gene sequence analyses revealed that the isolated strains belong to the genus Actinoallomurus. DNA–DNA hybridization values showed that the three strains belonged to a novel species of the genus Actinoallomurus. Therefore strains K08-0182T, K08-0178 and K08-0195 are proposed as representatives of a novel species, Actinoallomurus radicium sp. nov. The type strain is K08-0182T ( = DSM 45523T  = NBRC 107678T  = JCM 17294T).

Phytomonospora endophytica gen. nov., sp. nov., isolated from the roots of Artemisia annua L

A novel endophytic actinomycete, strain YIM 65646T, was isolated from the roots of Artemisia annua L. collected from Yunnan Province, south-west China. Growth was observed in the temperature range 10–40 °C (optimum 20–28 °C) and at pH 6.0–9.0 (optimum pH 7.0). The organism formed well-developed, branched substrate mycelia, but aerial mycelium was not produced. Phenotypic characterization and 16S rRNA gene sequence analysis indicated that strain YIM 65646T belonged to the family Micromonosporaceae (sharing ≤93.6 % sequence similarity with members of this family) and formed a distinct clade in the Micromonosporaceae phylogenetic tree. The strain contained meso-diaminopimelic acid in the cell wall and mannose, ribose, galactose and glucose in whole-cell hydrolysates. The major menaquinones were MK-10(H4), MK-10(H2), MK-8(H2), MK-9(H2) and MK-10(H6). The major fatty acids were iso-C15 : 0, anteiso-C15 : 0, anteiso-C17 : 0, iso-C17 : 0 and iso-C16 : 0. The DNA G+C content of strain YIM 65646T was 70.0 mol%. On the basis of morphological and chemotaxonomic properties and phylogenetic analysis based on 16S rRNA gene sequence data, it is proposed that this strain should be classified in a novel genus and species, Phytomonospora endophytica gen. nov., sp. nov., in the family Micromonosporaceae. The type strain is YIM 65646T ( = CCTCC AA 209041T  = DSM 45386T).

Variation and predicted structure of the flagellin gene in Actinoplanes species

Members of the genus Actinoplanes are considered to be representative of motile actinomycetes. To infer the flagellar diversity of Actinoplanes species, novel degenerate primers were designed for the flagellin (fliC) gene. The fliC gene of 21 Actinoplanes strains was successfully amplified and classified into two groups based on whether they were large (type I) or small (type II). Comparison of the translated amino acid sequences revealed that this size difference could be attributed to large number of gaps located in the central variable region. However, the C- and N- terminal regions were conserved. Except for a region on the flagellum surface, structural predictions of type I and II flagellins revealed that the two flagellin types were strongly correlated with each other. Phylogenetic analysis of the 115-amino acid N-terminal sequences revealed that the Actinoplanes species formed three clusters, and type II flagellin gene containing three type strains were phylogenetically closely related each other.

Streptosporangium oxazolinicum sp. nov., a novel endophytic actinomycete producing new antitrypanosomal antibiotics, spoxazomicins

An actinomycete strain K07-0460(T) producing new antitrypanosomal antibiotics, spoxazomicins, was isolated from the roots of a variety of orchid collected in the subtropical Okinawa prefecture. The 16S ribosomal RNA gene sequence analysis indicated that the strain belonged to the genus Streptosporangium and showed high similarities with S. amethystogenes subsp. amethystogenes DSM 43179(T) (99.4%), S. amethystogenes subsp. fukuiense IFO 15365(T) (99.2%) and S. longisporum DSM 43180(T) (98.7%). The DNA-DNA hybridization relatedness values between strain K07-0460(T) and the three strains were below 70%. On the basis of phylogenetic analysis, DNA-DNA hybridization relatedness and physiological characteristics, the strain should be classified as a new species Streptosporangium oxazolinicum sp. nov. in the genus Streptosporangium. The type strain of S. oxazolinicum is K07-0460(T) (=JCM 17388(T)).

Jishengella endophytica gen. nov., sp. nov., a new member of the family Micromonosporaceae

A novel endophytic actinomycete, designated strain 202201(T), was isolated from an Acanthus illicifolius root collected from the mangrove reserve zone in Hainan Province, China. Phylogenetic analysis based on 16S rRNA gene sequences suggested that strain 202201(T) fell within the family Micromonosporaceae. The strain formed an extensively branched substrate mycelium, which carried uneven warty-surfaced spores. Cell walls of strain 202201(T) contained meso-diaminopimelic acid and xylose, mannose, arabinose, ribose and glucose were detected as whole-cell sugars. The acyl type of the cell-wall polysaccharides was glycolyl. The major menaquinones were MK-9(H(4)), MK-9(H(6)), MK-9(H(8)) and MK-10(H(4)). The polar lipids were phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylinositol mannoside and phosphatidylserine. The major cellular fatty acids were 10-methyl-C(17 : 0), iso-C(15 : 0), iso-C(16 : 0) and C(17 : 1)ω8c. The DNA G+C content was 72.3 mol%. On the basis of the morphological and chemotaxonomic characteristics, phylogenetic analysis and characteristic patterns of 16S rRNA gene signature nucleotides, strain 202201(T) ( = CGMCC 4.5597(T ) = DSM 45430(T)) represents a novel species of a new genus within the family Micromonosporaceae, for which the name Jishengella endophytica gen. nov., sp. nov. is proposed.