Actinobacteria Isolated from an Underground Lake and Moonmilk Speleothem from the Biggest Conglomeratic Karstic Cave in Siberia as Sources of Novel Biologically Active Compounds

Actinobacteria isolated from unstudied ecosystems are one of the most interesting and promising sources of novel biologically active compounds. Cave ecosystems are unusual and rarely studied. Here, we report the isolation and characterization of ten new actinobacteria strains isolated from an ancient underground lake and moonmilk speleothem from the biggest conglomeratic karstic cave in Siberia with a focus on the biological activity of the obtained strains and the metabolite dereplication of one active strain. Streptomyces genera isolates from moonmilk speleothem demonstrated antibacterial and antifungal activities. Some of the strains were able to inhibit the growth of pathogenic Candida albicans.     

The rhizospheres of traditional medicinal plants in Panxi, China, host a diverse selection of actinobacteria with antimicrobial properties

Actinobacteria are a prolific source of antibiotics. Since the rate of discovery of novel antibiotics is decreasing, actinobacteria from unique environments need to be explored. In particular, actinobacterial biocontrol strains from medicinal plants need to be studied as they can be a source of potent antibiotics. We combined culture-dependent and culture-independent methods in analyzing the actinobacterial diversity in the rhizosphere of seven traditional medicinal plant species from Panxi, China, and assessed the antimicrobial activity of the isolates. Each of the plant species hosted a unique set of actinobacterial strains. Out of the 64 morphologically distinct isolates, half were Streptomyces sp., eight were Micromonospora sp., and the rest were members of 18 actinobacterial genera. In particular, Ainsliaea henryi Diels. hosted a diverse selection of actinobacteria, although the 16S ribosomal RNA (rRNA) sequence identity ranges of the isolates and of the 16S rRNA gene clone library were not congruent. In the clone library, 40% of the sequences were related to uncultured actinobacteria, emphasizing the need to develop isolation methods to assess the full potential of the actinobacteria. All Streptomyces isolates showed antimicrobial activity. While the antimicrobial activities of the rare actinobacteria were limited, the growth of Escherichia coli, Verticillium dahliae, and Fusarium oxysporum were inhibited only by rare actinobacteria, and strains related to Saccharopolyspora shandongensis and Streptosporangium roseum showed broad antimicrobial activity.     

Molecular characterization of Antarctic actinobacteria and screening for antimicrobial metabolite production

The present study aimed to isolate actinobacteria from soil samples and characterized them using molecular tools and screened their secondary metabolites for antimicrobial activities. Thirty-nine strains from four different location of Barrientos Island, Antarctica using 12 types of isolation media was isolated. The isolates were preceded to screening of secondary metabolites for antimicrobial and antifungal activities. Using high-throughput screening methods, 38% (15/39) of isolates produced bioactive metabolites. Approximately 18% (7/39), 18% (7/39), 10% (4/39) and 2.5% (1/39) of isolates inhibited growth of Candida albicans ATCC 10231^T, Staphylococcus aurues ATCC 51650^T, methicillin-resistant Staphylococcus aurues (MRSA) ATCC BAA-44^T and Pseudomonas aeruginosa ATCC 10145^T, respectively. Molecular characterization techniques like 16S rRNA analysis, Enterobacterial repetitive intergenic consensus—polymerase chain reaction (ERIC-PCR), Random amplified polymorphic DNA (RAPD) and composite analyses were used to characterize the actinobacteria strains. Analysis of 16S rRNA sequences is still one of the most powerful methods to determine higher taxonomic relationships of Actinobacteria. Both RAPD and ERIC-PCR fingerprinting have shown good discriminatory capability but RAPD proved to be better in discriminatory power than ERIC-PCR. Our results demonstrated that composite analysis of both fingerprinting generally increased the discrimination ability and generated best clustering for actinobacteria strains in this study.     

Diversity and antibacterial activity of culturable actinobacteria isolated from five species of the South China Sea gorgonian corals

This study describes the diversity and antibacterial activity of culturable actinobacteria isolated from five species of gorgonian corals (Echinogorgia aurantiaca, Melitodes squamata, Muricella flexuosa, Subergorgia suberosa, and Verrucella umbraculum) collected in shallow water of the South China Sea. A total of 123 actinobacterial isolates were recovered using ten different isolation media, and assigned to 11 genera, including Streptomyces and Micromonospora as the dominant genera, followed by Nocardia, Verrucosispora, Nocardiopsis, Rhodococcus, Pseudonocardia, Agrococcus, Saccharomonospora, Saccharopolyspora and Dietzia. Comparable analysis indicated that the numbers of actinobacterial genera and isolates from the five gorgonian coral species varied significantly. It was found that 72 isolates displayed antibacterial activity against at least one indicator bacterium, and the antibacterial strains isolated from different gorgonians had almost the same proportion (~50 %). These results provide direct evidence for the hypotheses that gorgonian coral species contain large and diverse communities of actinobacteria, and suggest that many gorgonian-associated actinobacteria could produce some antibacterial agents to protect their hosts against pathogens. To our knowledge, this is the first report about the diversity of culturable actinobacteria isolated from gorgonian corals.     

川楝内生放线菌多样性及抗菌活性筛选

【目的】探究药用植物川楝内生放线菌多样性,从中挖掘出新的放线菌菌株,发现新的潜在农业生防和医药先导化合物。【方法】从四川境内的资阳、遂宁以及重庆万州采集川楝的根、茎、叶、果、皮,采用纯培养方法,用4种培养基共分离获得148株放线菌。通过形态学观察筛选出60株放线菌进行RFLP分析,选出代表菌株进行16S r RNA基因序列分析。以3株细菌和6株病原真菌作为指示菌株,检测初筛出的60株菌株的抗菌活性以及聚酮合酶(PKSⅠ、PKSⅡ)基因、非核糖体多肽合成酶(NRPS)基因和卤化酶(Halo)基因。【结果】基于16S r RNA-RFLP分析,60株放线菌被分成10簇,筛选出25株代表菌株分别属于7个属,包括Streptomyces、Micromonospora、Planotetraspora、Streptosporangium、Nocardiopsis、Prauseria、Microbispora,其中链霉菌占73.3%。供试的川楝内生放线菌对细菌、真菌有不同程度的抗菌活性;其中含有4类化合物合成基因的菌株占10%-55%。【结论】药用植物川楝内生放线菌具有丰富的多样性,且不同地区不同部位川楝组织中放线菌的种群存在差异;分离菌株广谱的抗菌活性证明,川楝内生放线菌在次生代谢产物合成方面具有巨大潜力,这为进一步的药物开发提供了丰富的菌种资源。     

青藏高原阿里、那曲和海西地区土壤可培养放线菌的多样性

【目的】为了研究青藏高原北部地区土壤可培养放线菌的多样性,并比较不同选择性分离培养基对高原土壤放线菌的分离效果。【方法】使用9种分离培养基,并尝试添加藤黄微球菌发酵液,对采集自阿里、那曲和海西地区的14份土壤样品中的放线菌进行选择性分离。通过16S r RNA基因序列分析对分离菌株进行初步分类鉴定,并在不同分类水平上统计所分离得到的放线菌多样性。【结果】分离得到去重复后的放线菌255株,分布于放线菌门的8个目,14个科,23个属,包含94个可能的物种。其中至少25个物种可能为新种,分布于13个属。链霉菌属的菌株108株,可能的物种28个,是最主要的优势菌属。分离培养基中添加藤黄微球菌发酵液明显增加了放线菌分离菌株的数量和多样性,稀释的葡萄糖酵母麦芽汁培养基适合分离链霉菌,淀粉甘油脯氨酸培养基、丙酸钠酪蛋白培养基等则适合分离稀有放线菌。【结论】青藏高原北部土壤放线菌多样性非常丰富,并且存在较多的新颖放线菌类群;添加藤黄微球菌发酵液是提高放线菌分离效率的有效手段。     

Saccharopolyspora karakumensis sp. nov., Saccharopolyspora elongata sp. nov., Saccharopolyspora aridisoli sp. nov., Saccharopolyspora terrae sp. nov. and their biotechnological potential revealed by genome analysis

Exploration of unexplored habitats for novel actinobacteria with high bioactivity potential holds great promise in the search for novel entities. During the course of isolation of actinobacteria from desert soils, four actinobacteria, designated as 5K548^T, 7K502^T, 16K309^T and 16K404^T, were isolated from the Karakum Desert and their bioactivity potential as well as taxonomic provenances were revealed by comprehensive genome analyses. Pairwise sequence analyses of the 16S rRNA genes indicated that the four strains are representatives of putatively novel taxa within the prolific actinobacterial genus Saccharopolyspora. The strains have typical chemotaxonomic characteristics of the genus Saccharopolyspora by having meso-diaminopimelic acid as diagnostic diaminoacid, arabinose, galactose and ribose as whole-cell sugars. Consistent with this assignment, all of the isolates contained phosphatidylcholine in their polar lipid profiles and MK-9(H₄) as the predominant menaquinone. The sizes of the genomes of the isolates ranged from 6.0 to 10.2 Mb and the associated G + C contents from 69.6 to 69.7 %. Polyphasic characterizations including determination of overall genome relatedness indices revealed that the strains are representatives of four novel species in the genus Saccharopolyspora. Consequently, isolates 5K548^T, 7K502^T, 16K404^T and 16K309^T are proposed as novel Saccharopolyspora species for which the names of Saccharopolyspora karakumensis sp. nov., Saccharopolyspora elongata sp. nov., Saccharopolyspora aridisoli sp. nov. and Saccharopolyspora terrae sp. nov. are proposed, respectively. Comprehensive genome analysis for biosynthetic gene clusters showed that the strains have high potential for novel secondary metabolites. Moreover, the strains harbour many antimicrobial resistance genes providing more evidence for their potentiality for bioactive metabolites.     

塔里木盆地胀果甘草内生放线菌多样性及抗菌活性分析

【目的】发掘具有开发前景的放线菌资源,对分离自新疆胀果甘草的内生放线菌的多样性、抗菌活性和次级代谢产物合成相关基因进行研究。【方法】采用5种培养基和3种前处理方法,从胀果甘草中分离获得80株放线菌。基于菌株形态学特征,对36株代表菌株进行抗菌活性检测,通过特异性引物扩增方法,检测了PKS I、PKS II、NPRS和卤化酶基因,探究其合成天然产物的潜在能力。结合筛选结果,选取其中20株代表菌,经16S r RNA基因测序,对其进行系统发育分析。【结果】培养基E2和E3结合热处理的分离效果较好;86.1%的代表菌株对供试的细菌、病原真菌表现出了不同程度的抗菌活性,PKS I、PKS II、NRPS基因和卤化酶基因阳性检出率分别为16.7%、72.2%、25.0%和11.1%。具有活性功能的代表菌株经16S r RNA基因测序分析,分别属于链霉菌属(Streptomyces)、小单胞菌属(Micromonospora)、红球菌属(Rhodococcus)和游动放线菌属(Actinoplanes)4个属,其中链霉菌属(Streptomyces)为优势菌属,占60%以上。【结论】胀果甘草是我国传统的药用植物,其植株内部蕴藏着丰富的放线菌资源,并在次生代谢产物合成方面拥有巨大潜力,具有进一步开发的价值。     

贵州兴义喀斯特洞穴可培养放线菌多样性及抗菌活性初筛

【目的】进一步了解兴义喀斯特洞穴可培养放线菌资源及产活性代谢产物的能力。【方法】选取多种分离培养基,利用稀释直接涂布平板法对贵州黔西南兴义市多个喀斯特洞穴的土壤和岩石进行可培养放线菌资源分离;利用三种发酵培养基对相关放线菌进行生物产物初筛。【结果】根据16S rRNA基因序列的比对分析,将分离得到的251株放线菌分别归类到44个属,其中链霉菌属(Streptomyces)占分离菌株的比例为24.30%,小单孢菌属(Micromonospora)占比11.95%,红球菌属(Rhodococcus)占比9.16%,微杆菌属(Microbacterium)占比7.17%,诺卡氏菌属(Nocardia)占比6.37%,该五类放线菌为该地区可培养放线菌的优势菌群。对70株细菌进行活性次级代谢产物筛选,其中35株放线菌对指示菌具有抑制活性,且主要类群为链霉菌属和小单孢菌属。【结论】贵州兴义喀斯特洞穴中存在丰富多样的放线菌类群,且蕴藏大量具有产生活性次级代谢产物能力的菌株,为医药产业提供潜力菌株资源,极具进一步发掘和研究的价值。     

Phylogenetic diversity and investigation of plant growth-promoting traits of actinobacteria in coastal salt marsh plant rhizospheres from Jiangsu,China

Actinobacteria from special habitats are of interest due to their producing of bioactive compounds and diverse ecological functions. However, little is known of the diversity and functional traits of actinobacteria inhabiting coastal salt marsh soils. We assessed actinobacterial diversity from eight coastal salt marsh rhizosphere soils from Jiangsu Province, China, using culture-based and 16S rRNA gene high throughput sequencing (HTS) methods, in addition to evaluating their plant growth-promoting (PGP) traits of isolates. Actinobacterial sequences represented 2.8%–43.0% of rhizosphere bacterial communities, as determined by HTS technique. The actinobacteria community comprised 34 families and 79 genera. In addition, 196 actinobacterial isolates were obtained, of which 92 representative isolates were selected for further 16S rRNA gene sequencing and phylogenetic analysis. The 92 strains comprised seven suborders, 12 families, and 20 genera that included several potential novel species. All representative strains were tested for their ability of producing indole acetic acid (IAA), siderophores, 1-aminocyclopropane-1-carboxylate deaminase (ACCD), hydrolytic enzymes, and phosphate solubilization. Based on the presence of multiple PGP traits, two strains, Streptomyces sp. KLBMP S0051 and Micromonospora sp. KLBMP S0019 were selected for inoculation of wheat seeds grown under salt stress. Both strains promoted seed germination, and KLBMP S0019 significantly enhanced seedling growth under NaCl stress. Our study demonstrates that coastal salt marsh rhizosphere soils harbor a diverse reservoir of actinobacteria that are potential resources for the discovery of novel species and functions. Moreover, several of the isolates identified here are good candidates as PGP bacteria that may contribute to plant adaptions to saline soils.     

Isolation and Identification of Actinobacteria from Surface-Sterilized Wheat Roots

This is the first report of filamentous actinobacteria isolated from surface-sterilized root tissues of healthy wheat plants (Triticum aestivum L.). Wheat roots from a range of sites across South Australia were used as the source material for the isolation of the endophytic actinobacteria. Roots were surface-sterilized by using ethanol and sodium hypochlorite prior to the isolation of the actinobacteria. Forty-nine of these isolates were identified by using 16S ribosomal DNA (rDNA) sequencing and found to belong to a small group of actinobacterial genera including Streptomyces, Microbispora, Micromonospora, and Nocardiodes spp. Many of the Streptomyces spp. were found to be similar, on the basis of their 16S rDNA gene sequence, to Streptomyces spp. that had been isolated from potato scabs. In particular, several isolates exhibited high 16S rDNA gene sequence homology to Streptomyces caviscabies and S. setonii. None of these isolates, nor the S. caviscabies and S. setonii type strains, were found to carry the nec1 pathogenicity-associated gene or to produce the toxin thaxtomin, indicating that they were nonpathogenic. These isolates were recovered from healthy plants over a range of geographically and temporally isolated sampling events and constitute an important plant-microbe interaction.     

Screening and isolation of halophilic bacteria producing extracellular hydrolyses from Howz Soltan Lake,Iran

Screening of bacteria from different areas of Howz Soltan playa, a hypersaline lake in the central desert zone of Iran, led to the isolation of 231 moderately halophilic bacteria, which were able to grow optimally in media with 5–15% of salt, and 49 extremely halophilic microorganisms that required 20–25% of salt for optimal growth. These isolates produced a great variety of extracellular hydrolytic enzymes. A total of 195, 177, 100, 95, 92, 68, 65, 33, and 28 strains produced lipases, amylases, proteases, inulinases, xylanases, cellulases, pullulanases, DNases, and pectinases, respectively. In comparison with gram-negative bacteria, the gram-positive halophilic rods, showed more hydrolytic activities. Several combined activities were showed by some of these isolates. One strain presented 9 hydrolytic activities, 4 strains presented 8 hydrolytic activities, 10 strains presented 7 hydrolytic activities and 29 strains presented 6 hydrolytic activities. No halophilic isolate without hydrolytic activity has been found in this study. According to their phenotypic characteristics and comparative partial 16S rRNA sequence analysis, the halophilic strains were identified as members of the genera: Salicola, Halovibrio, Halomonas, Oceanobacillus, Thalassobacillus, Halobacillus, Virgibacillus, Gracilibacillus, Salinicoccus, and Piscibacillus. Most lipase and DNase producers were members of the genera Gracilibacillus and Halomonas, respectively, whereas most of the isolates able to produce hydrolytic enzymes such as amylase, protease, cellulose (CMCase) and inulinase, belonged to gram-positive genera, like Gracilibacillus, Thalassobacillus, Virgibacillus, and Halobacillus.     

Screening and identification of actinobacteria from marine sediments: Investigation of potential producers for antimicrobial agents and type I polyketides

Marine actinobacteria were isolated from the sediment samples collected in Xinghai Bay, Xiaoping Island and Changhai in Dalian, China. Fifteen selective media were employed, of which Humic acid-Vitamin medium recovered the highest number of isolates. Eleven of the 239 isolates obtained from the selective media were selected for further investigations based on colony morphology and pigment formation. Phylogenetic analysis of their 16S rRNA sequences showed that these strains belong to the genera of Streptomyces and Micromonospora. One of these strains identified is a new species of Streptomyces. Type I polyketide synthase (PKSI) gene fragments were amplified from three strains. The PKSI sequence of one of these strains (S187) showed high homology to the KS gene involved in meridamycin biosynthesis. Based on this result, the neurotrophic activity of S187 was further investigated. Culture broth of S187 was applied to rat pheochromocytoma (PC12) cells, and a 2.3-fold increase in growth over control cells was observed by the 3-(4,5-dimethylthiazolyl)-2,5-diphenyltetrazolium bromide assay. These results indicated the importance of further exploration of the marine actinobacteria in Dalian sea area for antimicrobial agents and type I polyketides.     

Isolation and characterization of culturable endophytic actinobacteria associated with Artemisia annua L.

Endophytic actinobacteria isolated from Artemisia annua were characterized and evaluated for their bioactivities. A total of 228 isolates representing at least 19 different genera of actinobacteria were obtained and several of them seemed to be novel taxa. An evaluation of antimicrobial activity showed that more isolates possessed activity towards plant pathogens than activity against other pathogenic bacteria or yeasts. High frequencies of PCR amplification were obtained for type I polyketide synthases (PKS-I, 21.1%), type II polyketide synthases (PKS-II, 45.2%) and nonribosomal peptide synthetases (NRPS, 32.5%). The results of herbicidal activity screening indicated that 19 out of 117 samples of fermentation broths completely inhibited the germination of Echinochloa crusgalli. This study indicated that endophytic actinobacteria associated with A. annua are abundant and have potentially beneficial and diverse bioactivities which should be pursued for their biotechnical promise.     

Rare taxa and dark microbial matter: novel bioactive actinobacteria abound in Atacama Desert soils

An “in house” taxonomic approach to drug discovery led to the isolation of diverse actinobacteria from hyper-arid, extreme hyper-arid and very high altitude Atacama Desert soils. A high proportion of the isolates were assigned to novel taxa, with many showing activity in standard antimicrobial plug assays. The application of more advanced taxonomic and screening strategies showed that strains classified as novel species of Lentzea and Streptomyces synthesised new specialised metabolites thereby underpinning the premise that the extreme abiotic conditions in the Atacama Desert favour the development of a unique actinobacterial diversity which is the basis of novel chemistry. Complementary metagenomic analyses showed that the soils encompassed an astonishing degree of actinobacterial ‘dark matter’, while rank-abundance analyses showed them to be highly diverse habitats mainly composed of rare taxa that have not been recovered using culture-dependent methods. The implications of these pioneering studies on future bioprospecting campaigns are discussed.     

河北九莲城淖尔可培养放线菌多样性及抗菌活性筛选

【目的】勘探干涸的九莲城淖尔土壤放线菌多样性并进行活性筛选,以期发现药用微生物资源,为新抗生素的发现奠定基础。【方法】采用15种分离培养基,以稀释涂布法分离放线菌;根据分离菌株的16S rRNA基因序列同源性分析放线菌多样性;发酵液经乙酸乙酯萃取,菌丝体经丙酮浸提,获得提取浓缩物样品;样品通过纸片扩散法进行抗菌活性初筛;抗菌阳性菌株采用PCR技术进行Ⅰ型聚酮合酶(PKS I)KS域、Ⅱ型聚酮合酶(PKS II)KS域和非核糖体多肽合成酶(NRPS)A结构域抗生素生物合成基因的检测。【结果】从11份盐湖土壤样品中分离纯化到251株放线菌,其分布于放线菌纲的10个目15个科31个属,其中优势菌属为链霉菌属和拟诺卡氏菌属;251株放线菌中包括57株耐(嗜)盐放线菌,其优势菌属为拟诺卡氏菌属(22株)和涅斯捷连科氏菌属(15株)。基于16S r RNA基因序列的系统发育分析显示,菌株J11Y309为糖霉菌科潜在新属,菌株J12GA03为分枝杆菌科潜在新种。96株放线菌活性检测结果显示,56株至少对1株检定菌具有抗菌活性,阳性率为58.3%;56株有活性的放线菌中,47株至少含有1种抗生素生物合成基因,其中17株同时具有3种抗生素生物合成基因。【结论】干涸的九莲城淖尔土壤中含有较为丰富的药用放线菌资源,具有从中发现放线菌新物种和新抗生素的潜力。     

Antimicrobial properties of endophytic actinomycetes isolated from <Emphasis Type="Italic">Combretum latifolium</Emphasis> Blume,a medicinal shrub from Western Ghats of India

Endophytic actinomycetes were isolated from Combretum latifolium Blume (Combretaceae),Western Ghats of Southern India and identified by its characteristic culture morphology and molecular analysis of 16S rRNA gene sequences. In this survey of endophytic actinomycetes, a total of 117 isolates representing 9 different genera of endophytic actinomycetes were obtained using four different isolation media and several of them seemed to be novel taxa. Streptomyces genera (35%) was the most frequently isolated strains, followed by Nocordiopsis (17%) and Micromonospora (13%). ISP-4 medium recovered more isolates (47%) when compared to rest of the media used. Preliminary antibacterial activity of the isolates was carried out by confrontation test. Ethyl acetate fraction of selected isolates in disc diffusion assay exhibited broad spectrum antimicrobial activity against test human pathogens. All Streptomyces spp. strains displayed significant antimicrobial activity against test pathogens. Strain CLA-66 and CLA-68 which are Nocordipsis spp. inhibited both bacterial and fungal pathogens where as other isolates inhibited atleast three test human pathogens in disc diffusion assay. Antimicrobial screening of endophytic actinomycetes from this host may represent a unique potential niche for antimicrobial compounds of industrial and pharmaceutical applications. This work is the first comprehensive report on incidence of potential endophytic actinomycetes inhabiting C. latifolium Blume.     

广西山口红树林内生放线菌的分离、筛选及初步鉴定

从广西山口国家红树林生态自然保护区采集8种真红树植物和5种半红树植物的根、茎、叶及胚轴等组织样品共计41份。经过表面消毒后粉碎,分别以几丁质、腐殖酸、木聚糖等作为主要营养及能量来源设计了8种分离培养基,从植物组织中分离得到118株放线菌。使用6种新药筛选模型对分离菌株进行了生理活性筛选,77株放线菌的发酵液样品在一个或多个药物筛选模型中显示为阳性,初筛阳性率为65.3%。对77株筛选阳性菌株进行的初步分类研究结果显示,其中44株属于链霉菌属,25株为小单孢属的菌株,3株属于糖丝菌属,3株为诺卡氏属菌株,1株是拟诺卡氏属菌株,1株是伦茨氏菌属的菌株。对一株在抗多重耐药检定菌HH22和降血脂模型上都显示出良好活性的菌株I07A-01824进行表型和基因型分析,确定I07A-01824为黄白链霉菌(Streptomyces albidoflavus)菌株。该研究显示,红树植物内生环境不仅仅孕育了丰富多样的内生放线菌,而且红树植物内生放线菌也是新型天然生理活性次级代谢产物的有效来源。     

Culturable Actinobacteria from the Marine Sponge Hymeniacidon perleve: Isolation and Phylogenetic Diversity by 16S rRNA gene-RFLP Analysis

A total of 106 actinobacteria associated with the marine sponge Hymeniacidon perleve collected from the Yellow Sea, China were isolated using eight different media. The number of species and genera of actinobacteria recovered from the different media varied significantly, underlining the importance of optimizing the isolation conditions. The phylogenetic diversity of the actinobacteria isolates was assessed using 16S rRNA gene amplification–restriction fragment length polymorphism (RFLP) analysis of the 106 strains with different morphologies. The RFLP fingerprinting of selected strains by HhaI-digestion of the 16S rRNA genes resulted in 11 different patterns. The HhaI-RFLP analysis gave good resolution for the identification of the actinobacteria isolates at the genus level. A phylogenetic analysis using 16S rRNA gene sequences revealed that the isolates belonged to seven genera of culturable actinobacteria including Actinoalloteichus, Micromonospora, Nocardia, Nocardiopsis, Pseudonocardia, Rhodococcus, and Streptomyces. The dominant genus was Streptomyces, which represented 74% of the isolates. Three of the strains identified are candidates for new species.     

Diversity and physiological properties of root endophytic actinobacteria in native herbaceous plants of Korea

Endophytic actinobacterial diversity in the native herbaceous plant species of Korea was analyzed using a culture-based approach. Sixty one actinobacterial strains were isolated, and assigned to 15 genera based on 16S rRNA gene analysis. The members of the genus Streptomyces comprised 45.9% of the total isolates, followed by Micromonospora (18.8%), Rhodococcus (6.6%), Microbispora (4.9%), and Micrococcus (4.9%). Other minor constituents included members of Microbacterium, Streptacidiphilus, Arthrobacter, Dietzia, Kitasatospora, Herbiconiux, Mycobacterium, Nocardia, Rathayibacter, and Tsukamurella. Among the isolates, 65.6% exhibited at least one hydrolytic enzyme activity out of four, and 45.9% exhibited antagonistic activity against at least one fungal pathogen out of five, thus demonstrating that endophytic actinobacteria can be an important source of bioactive compounds. Notably, most strains of Streptomyces proved active for both enzymatic and antagonistic activities.