Solihabitans fulvus gen. nov., sp. nov., a member of the family Pseudonocardiaceae isolated from soil.

A polyphasic taxonomic study was carried out on an actinobacterial strain (AN110305T) isolated from soil sampled in the Republic of Korea. Cells of the strain were Gram-stain-positive, aerobic, non-motile and rod-shaped. Comparative 16S rRNA gene sequence studies showed a clear affiliation of strain AN110305T with Actinomycetia, with highest pairwise sequence similarities to Goodfellowiella coeruleoviolacea DSM 43935T (97.6%), Umezawaea tangerina MK27-91F2T (97.0%), Kutzneria chonburiensis NBRC 110610T (96.9%), Kutzneria buriramensis A-T 1846T (96.8%), Umezawaea endophytica YIM 2047XT (96.8%), Kutzneria albida NRRL B-24060T (96.7%) and Saccharothrix coeruleofusca NRRL B-16115T (96.6%). Cells of strain AN110305T formed pale-yellow colonies on Reasoner's 2A agar. MK-9 (H4) (68%) and MK-10 (H4) (32%) were the predominant menaquinones. Diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylmethyl ethanolamine, hydroxy-phosphatidylethanolamine, an unidentified aminolipid and an unidentified aminophospholipid were major polar lipids. Iso-C16:0 (24.5%), anteiso-C15:0 (19.3%), anteiso-C17:0 (15.7%) and iso-C15:0 (15.2%) were the major fatty acids and meso-diaminopimelic acid was the pepdidoglycan. The cell-wall sugars were composed of galactose, glucose, mannose and ribose. The genomic DNA G+C content was 70.7 mol%. Based on genotypic and phenotypic data, strain AN110305T could be distinguished from all genera within the family Pseudonocardiaceae and represents a novel genus and species named Solihabitans fulvus gen. nov., sp nov. The type strain is AN110305T (=KCTC 39307T =DSM 103572T).

Salinarimonas soli sp. nov., isolated from soil.

A light pink coloured bacterium, designated strain BN140002T, was isolated from a soil sample collected in Goesan-gun, Chungcheongbuk-do, Republic of Korea. Cells of strain BN140002T were Gram-stain-negative, aerobic, motile and rod-shaped. Phylogenetic analysis based on 16S rRNA gene sequences showed 94.7, 94.7, 93.9, 93.3, 93.4 and 93.0% similarities to Salinarimonas rosea KCTC 22346T, Salinarimonas ramus DSM 22962T, Saliniramus fredricksonii HL-109T, Microvirga soli R491T, Chelatococcus caeni EBR-4-1T and Chelatococcus composti PC-2T, respectively. The major polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylcholine and phosphatidylethanolamine. The major cellular fatty acids were summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c) and summed feature 1 (C12 : 0 aldehyde and/or unknown 10.98) and the predominant ubiquinone was Q-10. The genomic DNA G+C content of strain BN140002T was 70.1 mol%. The genomic orthoANI values between strain BN140002T and Salinarimonas rosea KCTC 22346T and Salinarimonas ramus DSM 22962T were 75.0 and 74.8 %, respectively. Strain BN140002T had a class I-C type CRISPR-Cas system (CRISPR-associated helicase Cas3, CRISPR-associated protein Cas8c, CRISPR-associated protein Cas7, CRISPR-associated RecB family exonuclease Cas4, CRISPR-associated protein 1, 2). Based on phenotypic, chemotaxonomic and phylogenetic data, strain BN140002T should be assigned as a novel species of the genus Salinarimonas, for which the name Salinarimonas soli sp. nov. is proposed. The type strain is BN140002T (=KCTC 42643T=CCTCC AB 2017173T).

Description of desferrioxamine-producing bacterium Chitinophaga agrisoli sp. nov., isolated from soil.

A Gram-stain-negative, non-motile, yellow-pigmented and non-spore forming rod-shaped bacterium, designated strain BN140078T, was isolated from farmland soil, Chungbuk, Republic of Korea. It was able to grow aerobically at 10-40 °C (optimum 28 °C), pH 5.5-7.5 (optimum pH 7.0) and with 0-2.0% (w/v) NaCl concentration (optimum 1.0%) on Reasoner's 2A (R2A) agar medium. Comparative 16S rRNA gene sequence analysis showed that the strain BN140078T had 96.9%, 96.5% and 96.1% 16S rRNA gene similarities with Chitinophaga ginsengihumi KACC 17604T, Chitinophaga rupis KACC 14521T and Chitinophaga japonensis KACC 12057T, respectively. The predominant respiratory quinone was menaquinone MK-7 and the major fatty acids (≥ 5%) were C16:1 ω5c, iso-C15:0, iso-C17:0 3-OH and Summed Feature 3 (C16:1 ω7c and/or C16:1 ω6c). The polar lipids were composed of phosphatidylethanolamine, four unidentified amino lipids and six unidentified lipids. The genomic DNA G+C content was 49.5 mol%. The genome of strain BN140078T comprises a number of biosynthetic gene clusters for secondary metabolites, in particular those for non-ribosomal peptide products. The polyphasic taxonomic study clearly distinguished this strain from its closest phylogenetic neighbors. Thus, we propose that the BN140078T represents a novel species of the genus Chitinophaga, for which the name Chitinophaga agrisoli sp. nov. was proposed. The type strain is BN140078T (=KCTC 62555T = CCTCC AB 2018162T).

Flavitalea flava sp. nov., a bacterium isolated from a soil sample, and emended description of the genus Flavitalea.

A Gram-stain negative strain, designated AN120636T, was isolated from a soil sample collected from Goesan-gun, Chungbuk, South Korea. The strain was strictly aerobic, with golden yellow-pigmented colonies on R2A agar. Cells were non-motile, long or short rods and some were observed to be coccal. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain AN120636T belongs to the genus Flavitalea in the family of Chitinophagacea, with Flavitalea populi (95.4%), Pseudoflavitalea soli (95.0%), Flavitalea gansuensis (94.7%) and Pseudoflavitalea rhizosphaerae (94.7%) as its close relatives. Growth was observed at 15-32 °C, pH 5.0-7.0 and in the absence of NaCl. The strain contained iso-C17:0 3-OH, iso-C15:1 G and iso-C15:0 as its major cellular fatty acids; phosphatidylethanolamine as the major polar lipid; MK-7 as its respiratory quinone; and the polyamine was homospermidine. The genomic DNA G+C content was 44.8 mol%. On the basis of the polyphasic evidence, strain AN120636T is considered to represent a novel species, for which the name Flavitalea flava sp. nov. is proposed. The type strain is AN120636T (=KCTC 52346T=CCTCC AB 2017174T).

Aurantisolimonas haloimpatiens gen. nov., sp. nov., a bacterium isolated from soil.

A Gram-stain negative, strictly aerobic and non-motile bacterium, designated strain BN130233T, was isolated from a soil sample collected from Gyeongsangbuk-do, Republic of Korea. Colonies were orange in colour, with wet and smooth surfaces. Phylogenetic analyses based on the 16S rRNA gene sequences resulted in strain BN130233T forming a cluster with members of the family Chitinophagaceae Kämpfer et al. 2011, while sharing the highest sequence identity of 91.2 % with Chitinophaga niastensis JS16-4T. Good growth was observed at 20-28 °C, pH 7.0 and in the absence of NaCl. The major fatty acids were summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c), iso-C15 : 1 G, iso-C15 : 0 and iso-C17 : 0 3-OH. The respiratory quinone was MK-7. Major polar lipids contained phosphatidylethanolamine, an unidentified phospholipid, three unidentified aminolipids and eight unidentified lipids. The genomic DNA G+C content was 40.6 mol%. Phenotypic and chemotaxonomic characteristics together with 16S rRNA gene sequence analyses showed that strain BN130233T was distinct from its close phylogenetic relatives in the family ChitinophagaceaeKämpfer et al. 2011. The strain is, therefore, proposed as a representative of a new genus and new species with the name Aurantisolimonas haloimpatiens. The type strain of Aurantisolimonas haloimpatiens is BN130233T (=CCTCC AB 2017051T=KCTC 42642T).

Stackebrandtia soli sp. nov., a novel actinobacterium isolated from a soil sample.

An aerobic actinobacterium, strain AN130378T, was isolated from a soil sample collected in Korea and subjected to taxonomic investigation using a polyphasic approach. Phylogenetic analysis based on 16S rRNA gene sequence data showed that strain AN130378T is a member of the genus Stackebrandtia, with sequence similarities of 97.3 % to Stackebrandtia albiflava YIM 45751T and 97.1 % to Stackebrandtia endophytica YIM 64602T. The whole-cell hydrolysates contained meso-diaminopimelic acid as the diagnostic diamino acid, and galactose, glucose and xylose. The major menaquinones were MK-11(H4), MK-10(H4) and MK-11(H6), while the major fatty acids were identified as iso-C15 : 0, anteiso-C17 : 0, anteiso-C15 : 0, iso-C17 : 0 and summed feature 3 (C16 : 1ω6c and/or C16 : 1ω7c). The polar lipids were identified as diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylmethylethanolamine, an unidentified aminophospholipid, four unidentified glycolipids, three unidentified phospholipids and two unidentified polar lipids. The G+C content of the genomic DNA was determined to be 67.7 mol%. All chemotaxonomic and genotypic data indicated that the strain belongs to the genus Stackebrandtia. On the basis of morphological, chemotaxonomic data and phylogenetic analysis, strain AN130378T is considered to represent a novel species within the genus Stackebrandtia, for which the name Stackebrandtia soli sp. nov. is proposed. The type strain is AN130378T (=DSM 103573T=KCTC 39809T).

Actinorugispora endophytica gen. nov., sp. nov., an actinomycete isolated from Daucus carota.

An actinomycete strain, designated YIM 690008T, was isolated from Daucus carota collected from South Korea and its taxonomic position was investigated by using a polyphasic approach. The strain grew well on most media tested and no diffusible pigment was produced. The aerial mycelium formed wrinkled single spores and short spore chains, some of which were branched. The whole-cell hydrolysates contained meso-diaminopimelic acid, glucose, mannose, ribose, galactose and rhamnose. The predominant menaquinones were MK-10(H4), MK-10(H6), MK-10(H8) and MK-10(H2). The polar lipids were diphosphatidylglycerol, phosphatidylcholine, phosphatidylinositol, phosphatidylinositol mannosides, some unknown phospholipids, glycolipids and polar lipids. The major fatty acids were i-C16 : 0, ai-C17 : 0 and C18 : 1ω9c. The DNA G+C content of the genomic DNA was 63.1 mol%. Phylogenetic analysis indicated that the isolate belongs to the family Nocardiopsaceae. However, based on phenotypic, chemotaxonomic and genotypic data, it was concluded that strain YIM 690008T represents a novel genus and novel species of the family Nocardiopsaceae, for which the name Actinorugispora endophytica gen. nov., sp. nov. (type strain YIM 690008T = DSM 46770T = JCM 30099T = KCTC 29480T) is proposed.

Marinactinospora endophytica sp. nov., isolated from a medicinal plant.

A novel endophytic actinobacterium, designated strain YIM 690053(T), was isolated from healthy stems of Salsola ferganica Drob, and was characterized using a polyphasic taxonomic approach. The strain formed well-branched substrate mycelia with no fragmentation, and abundant aerial mycelia that differentiated into long spores. The strain was found to grow at 10-55 °C, pH 6.0-10.0 and in the presence of 0-7 % (w/v) NaCl. The genomic DNA G+C content was determined to be 70.5 mol%. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain YIM 690053(T) belongs to the genus Marinactinospora, and it shared the highest 16S rRNA gene sequence similarity with Marinactinospora thermotolerans SCSIO 00652(T) (98.96 %). However, the DNA-DNA relatedness values between the two strains was 37.85 ± 2.77 %. Based on the differences in the molecular and biochemical characteristics from its closest relative, strain YIM 690053(T) is concluded to represent a novel species of the genus Marinactinospora, for which the name Marinactinospora endophytica sp. nov. is proposed. The type strain is YIM 690053(T)(=KCTC 29664(T) = DSM 46799(T)).

Paenibacillus nicotianae sp. nov., isolated from a tobacco sample.

A Gram-stain positive, facultative anaerobic endospore-forming bacterium, designated strain YIM h-19(T), was isolated from a tobacco sample. Cells were observed to be motile rods by means of peritrichous flagella and colonies were observed to be convex, yellow, circular and showed catalase-positive and oxidase-negative reactions. Strain YIM h-19(T) was able to grow at 4-45 °C, pH 6.0-8.0 and 0-3 % NaCl (w/v). The predominant respiratory quinone was identified as MK-7. Major fatty acids were identified as anteiso-C15:0, anteiso-C17:0 and C16:0. The polar lipids were found to be phosphatidylethanolamine, diphosphatidylglycerol, phosphatidylglycerol and two unidentified polar lipids. The genomic DNA G+C content was determined to be 54 mol%. 16S rRNA gene sequence analysis showed the strain YIM h-19(T) was most closely related to Paenibacillus hordei RH-N24(T) and Paenibacillus hunanensis FeL05(T) with similarities of 98.30 and 94.64 % respectively. However, DNA-DNA hybridization data indicated that the isolate represented a novel genomic species with the genus Paenibacillus. All data from genotypic and phenotypic analyses support the conclusion that strain YIM h-19(T) represents a novel species of the genus Paenibacillus, for which the name Paenibacillus nicotianae sp. nov. is proposed. The type strain is YIM h-19(T) (=CGMCC1.12819(T) = NRRL B-59112(T)).

Streptomyces canchipurensis sp. nov., isolated from a limestone habitat.

Hundung Limestone habitat, Manipur, India is an unexplored site for microbial diversity studies. Using polyphasic taxonomy, a Streptomyces strain, MBRL 172(T), has been characterized. The strain was found to show highest 16S rRNA gene sequence similarity with Streptomyces coeruleofuscus NBRC 12757(T) (99.2 %). The DNA relatedness between MBRL 172(T) and S. coeruleofuscus NBRC 12757(T), and between MBRL 172(T) and Streptomyces nogalater NBRC 13445(T), were 36.8 ± 4.4 and 52.5 ± 2.7 %, respectively. Strain MBRL 172(T) was found to contain LL-diaminopimelic acid as the diagnostic diamino acid and glucose, mannose and xylose as the major sugars in whole cell hydrolysates. The polar lipids in the cell membrane were identified as diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositolmannoside. The predominant menaquinones detected were MK-9(H6) and MK-9(H8). The cellular fatty acids identified were mainly saturated fatty acids: anteiso-C15:0, iso-C16:0 and iso-C15:0. Based on differences in the biochemical and molecular characteristics from its closest relatives, the strain can be proposed to represent a novel taxon in the genus Streptomyces, for which the name Streptomyces canchipurensis is proposed, with the type strain MBRL 172(T) (=JCM 17575(T) = KCTC 29105(T)).

Rothia endophytica sp. nov., an actinobacterium isolated from Dysophylla stellata (Lour.) Benth.

A novel endophytic actinobacterium, designated strain YIM 67072(T), was isolated from healthy roots of Dysophylla stellata (Lour.) Benth. Cells of this aerobic, cream-yellow-coloured strain occurred singly, in pairs or in tetrads, were Gram-stain-positive and ovoid- to spherical-shaped. Strain YIM 67072(T) grew at 4-45 °C, pH 5.0-10.0 and in the presence of 0-7 % (w/v) NaCl. Phylogenetic analysis based on 16S rRNA gene sequences showed that strain YIM 67072(T) belonged to the genus Rothia. The isolate contained MK-7 as the major component of the quinone system. The peptidoglycan type was A3α. The polar lipid profile consisted predominantly of diphosphatidylglycerol and glycolipids. The major fatty acids were anteiso-C15 : 0, iso-C15 : 0, anteiso-C17 : 0 and iso-C16 : 0. The DNA G+C content was 53.2 mol%. However, strain YIM 67072(T) differed from its closest relatives Rothia nasimurium CCUG 35957(T) (98.5 % 16S rRNA gene sequence similarity), Rothia amarae JCM 11375(T) (97.6 %) and Rothia terrae L-143(T) (97.3 %) in many phenotypic characteristics. Moreover, the levels of DNA-DNA relatedness between the novel isolate and the three above-mentioned type strains were 28.7±1.3 %, 36.5±1.2 %, 46.8±1.5 %, respectively. Based on comparative analysis of physiological and chemotaxonomic data, strain YIM 67072(T) represents a novel species of the genus Rothia, for which the name Rothia endophytica sp. nov. is proposed. The type strain is YIM 67072(T) ( = DSM 26247(T) = JCM 18541(T)).

Streptomyces muensis sp. nov.

A strain of Streptomyces, MBRL 179(T), isolated from a sample from a Limestone quarry located at Hundung, Manipur, India, was characterized by polyphasic taxonomy. The strain formed a monophyletic clade with Streptomyces spinoverrucosus NBRC 14228(T) (16S rRNA gene sequence similarity of 99.3 %) in the Neighbour-joining tree. DNA-DNA hybridization experiment gave a DNA-DNA relatedness value of 34.7 % between MBRL 179(T) and S. spinoverrucosus NBRC 14228(T). Strain MBRL 179(T) contained LL-diaminopimelic acid, xylose, glucose, and mannose in the whole cell-wall hydrolysates along with small amount of ribose. The major polar lipids detected were diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, phosphatidylinositol and phosphatidylinositolmannoside, with other unknown phospholipids and aminophospholipid. MK-9(H6), MK-9(H8) and MK-9(H4) were the predominant menaquinones detected. The major fatty acids were anteiso-C16:0 (28.1 %), iso-C16:0 (20.3 %), C16:0 (9.4 %) and anteiso-C17:0 (8.3 %). The G+C content of the genomic DNA was 71.1 %. Based on the polyphasic experiment results, the strain MBRL 179(T) merits recognition as a representative of a novel species of the genus Streptomyces for which the name Streptomyces muensis sp. nov. is proposed; the type strain is MBRL 179(T) (=JCM 17576(T) = KCTC 29124(T)).

Thermus tengchongensis sp. nov., isolated from a geothermally heated soil sample in Tengchong, Yunnan, south-west China.

A Gram-stain negative aerobic bacterium, designated YIM 77924(T), was isolated from a geothermally heated soil sample collected at Rehai National Park, Tengchong, Yunnan province, south-west China. Growth was found to occur from 55 to 75 °C (optimum 65 °C), pH 6.0-8.0 (optimum pH 7.0) and 0-1 % NaCl (w/v). Cells were observed to be rod-shaped and the colonies convex, circular, smooth, yellow and non-transparent. Phylogenetic analysis based on the 16S rRNA gene sequence indicated that strain YIM 77924(T) belongs to the genus Thermus. The 16S rRNA gene sequence similarity values between strain YIM 77924(T) and other species of the genus Thermus were all below 97 %. The polar lipids of strain YIM 77924(T) were determined to be aminophospholipid, phospholipid and glycolipid. The predominant respiratory quinone was determined to be MK-8 and the G+C content was 66.64 mol%. The major fatty acids identified were iso-C(16:0), iso-C(15:0), iso-C(17:0) and C(16:0). On the basis of the morphological and chemotaxonomic characteristics as well as genotypic data, strain YIM 77924(T) is proposed to represent a novel species, Thermus tengchongensis sp. nov., in the genus Thermus. The type strain is YIM 77924(T) (=KCTC 32025(T) = CCTCC AB2012063(T)).

New discovery on the nematode activity of aureothin and alloaureothin isolated from endophytic bacteria Streptomyces sp. AE170020.

Endophytic bacteria, a rich source of bioactive secondary metabolites, are ideal candidates for environmentally benign agents. In this study, an endophytic strain, Streptomyces sp. AE170020, was isolated and selected for the purification of nematicidal substances based on its high nematicidal activity. Two highly active components, aureothin and alloaureothin, were identified, and their chemical structures were determined using spectroscopic analysis. Both compounds suppressed the growth, reproduction, and behavior of Bursaphelenchus xylophilus. In in vivo experiments, the extracts of strain Streptomyces sp. AE170020 effectively suppressed the development of pine wilt disease in 4-year-old plants of Pinus densiflora. The potency of secondary metabolites isolated from endophytic strains suggests applications in controlling Bursaphelenchus xylophilus and opens an avenue for further research on exploring bioactive substances against the pine wood nematode.

Nematicidal activity of teleocidin B4 isolated from Streptomyces sp. against pine wood nematode, Bursaphelenchus xylophilus.

BACKGROUND: Pine wilt disease (PWD) is a plant disease that causes serious damage to pine trees. PWD occurs when the host plant is infected with pinewood nematode (PWN), Bursaphelenchus xylophilus. In this study, a compound with nematicidal activity was isolated from actinomycetes and its efficacy was investigated in vitro. RESULT: We screened and selected Streptomyces sp. 680560, which had nematicidal activity against B. xylophilus. Based on 16S rRNA sequence analysis, it showed 99.93% similarity with Streptomyces blastmyceticus NRRB-5480T . Furthermore, the active compound was isolated and identified as teleocidin B4. Teleocidin B4 at concentrations ranging from 6.25 to 100 µM had low nematicidal activity after 24 and 36 h against adult and stage juveniles (J2) of B. xylophilus, but after 48 h nematicidal activity exceeded 95%. The rate of inhibition of egg hatching for Teleocidin B4 6.25, 12.5, 25, 50, and 100 µM was confirmed to be dose-dependently inhibited after 48 h of treatment. Teleocidin B4 is not only toxic to hatched B. xylophilus, but also affects egg hatching. CONCLUSION: This study was carried out to isolate actinomycete metabolites from pine tree endophytes from various natural environments for control of PWD. A compound with nematicidal activity was isolated from a selected strain and its structure was identified as teleocidin B4. The nematicidal effect of the isolated active substance, teleocidin B4, was confirmed. This is the first report of the effect of teleocidin B4 on B. xylophilus, suggesting its possibility as a PWD control agent. © 2020 Society of Chemical Industry.

Screening, isolation and evaluation of a nematicidal compound from actinomycetes against the pine wood nematode, Bursaphelenchus xylophilus.

BACKGROUND: Bursaphelenchus xylophilus is a migratory endoparasitic nematode known to cause severe environmental damage and economic losses in pine forest ecosystems. This present study investigated the nematicidal metabolites of actinomycetes in vitro and evaluated the disease control efficacy of the active compound and metabolites under greenhouse and field conditions. RESULTS: Five thousand types of actinobacteria from Korean forest soil samples were screened to identify novel nematicidal agents against the pine wood nematode. Streptomyces sp. AN091965 showed the strongest nematicidal activity. One active compound, spectinabilin, was obtained by nematicidal asssy-directed fractionation, and it showed significant nematicidal activity against B. xylophilus, with an LC50 value of 0.84 µg mL-1 . Spectinabilin effectively suppressed the development of pine wilt disease in 5-year-old Pinus densiflora trees, even at 0.9 mg per tree under greenhouse conditions. Moreover, the acetone extract of the active strain's mycelia efficiently suppressed the development of pine wilt disease under field conditions. CONCLUSION: To the best of our knowledge, this the first report to describe the nematicidal activity of spectinabilin against B. xylophilus. The cell extracts described herein merit further field studies as potential nematicides against the pine wood nematode. © 2018 Society of Chemical Industry.

Endophytic Actinobacteria Associated with Dracaena cochinchinensis Lour.: Isolation, Diversity, and Their Cytotoxic Activities.

Dracaena cochinchinensis Lour. is an ethnomedicinally important plant used in traditional Chinese medicine known as dragon's blood. Excessive utilization of the plant for extraction of dragon's blood had resulted in the destruction of the important niche. During a study to provide a sustainable way of utilizing the resources, the endophytic Actinobacteria associated with the plant were explored for potential utilization of their medicinal properties. Three hundred and four endophytic Actinobacteria belonging to the genera Streptomyces, Nocardiopsis, Brevibacterium, Microbacterium, Tsukamurella, Arthrobacter, Brachybacterium, Nocardia, Rhodococcus, Kocuria, Nocardioides, and Pseudonocardia were isolated from different tissues of D. cochinchinensis Lour. Of these, 17 strains having antimicrobial and anthracyclines-producing activities were further selected for screening of antifungal and cytotoxic activities against two human cancer cell lines, MCF-7 and Hep G2. Ten of these selected endophytic Actinobacteria showed antifungal activities against at least one of the fungal pathogens, of which three strains exhibited cytotoxic activities with IC50-values ranging between 3 and 33 µg·mL-1. Frequencies for the presence of biosynthetic genes, polyketide synthase- (PKS-) I, PKS-II, and nonribosomal peptide synthetase (NRPS) among these 17 selected bioactive Actinobacteria were 29.4%, 70.6%, and 23.5%, respectively. The results indicated that the medicinal plant D. cochinchinensis Lour. is a good niche of biologically important metabolites-producing Actinobacteria.

Characterization and evaluation of antimicrobial and cytotoxic effects of Streptomyces sp. HUST012 isolated from medicinal plant Dracaena cochinchinensis Lour.

A highly potent secondary metabolite producing endophytic strain, Streptomyces sp. HUST012 was isolated from the stems of the medicinal plant Dracaena cochinchinensis Lour. Strain HUST012 showed antimicrobial and antitumor activities which were significantly much higher than those of dragon's blood extracted from D. cochinchinensis Lour. On further analysis, the strain was found to produce two metabolites, SPE-B11.8 (elucidated to be a novel metabolite (Z)-tridec-7-ene-1,2,13-tricarboxylic acid) and SPE-B5.4 (elucidated as Actinomycin-D). The Minimum Inhibitory Concentration values of SPE-B11.8 against a set of test bacterial organisms (Methicillin-resistant Staphylococcus epidermis ATCC 35984, Methicillin-resistant Staphylococcus aureus ATCC 25923, Escherichia coli ATCC 25922, and Klebsiella pneumoniae ATCC 13883) ranged between 15.63 and 62.5 µg/ml while that for SPE-B5.4 ranged between 0.04 and 2.24 µg/ml. The compound SPE-B11.8 showed cytotoxic effect at 41.63 and 29.54 µg/ml IC 50-values against Hep G2 and MCF-7, respectively, while the compound SPE-B5.4 exhibited stronger activities against them at 0.23 and 0.18 µg/ml IC 50-values.