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To date, endophytic actinomycetes have been well-documented as great producers of novel antibiotics and important pharmaceutical leads. The present study aimed to evaluate potent bioactivities of metabolites synthesized by the strain LCP18 residing in the Vietnamese medicinal plant Litsea cubeba (Lour.) Pers towards human pathogenic bacteria and human cancer cell lines. Endophytic actinomycete strain LCP18 showed considerable inhibition against seven bacterial pathogens and three human tumor cell lines and was identified as species Streptomyces variabilis. Strain S. variabilis LCP18 was phenotypically resistant to fosfomycin, trimethoprim-sulfamethoxazole, dalacin, cefoxitin, rifampicin, and fusidic acid and harbored the two antibiotic biosynthetic genes such as PKS-II and NRPS. Further purification and structural elucidation of metabolites from the LCP18 extract revealed five plant-derived bioactive compounds including isopcrunetin, genistein, daidzein, syringic acid, and daucosterol. Among those, isoprunetin, genistein, and daidzein exhibited antibacterial activity against Salmonella typhimurium ATCC 14,028 and methicillin-resistant Staphylococcus epidermidis ATCC 35,984 with the MIC values ranging from 16 to 128 µg/ml. These plant-derived compounds also exhibited cytotoxic effects against human lung cancer cell line A549 with IC(50) values of less than 46 μM. These findings indicated that endophytic S. variabilis LCP18 can be an alternative producer of plant-derived compounds which significantly show potential applications in combating bacterial infections and inhibition against lung cancer cell lines.

Arterial/venous thrombosis is the major cardiovascular disorder accountable for substantial mortality; and the current demand for antithrombotic agents is extensive. Heparinases depolymerize unfractionated heparin (UFH) for the production of low molecular-weight heparins (LMWHs; used as anticoagulants against thrombosis). A microbial strain of Streptomyces sp. showing antithrombotic activity was isolated from the soil sample collected from north India. The strain was characterized by using 16S rRNA homology technique and identified as Streptomyces variabilis MTCC 12266 capable of producing heparinase enzyme. This is the very first communication reporting Streptomyces genus as the producer of heparinase. It was observed that the production of intracellular heparinase was [63.8 U/mg protein (specific activity)] 1.58 folds higher compared to extracellular heparinase [40.28 U/mg protein]. DEAE-Sephadex A-50 column followed by Sepharose-6B column purification of the crude protein resulted 19.18 folds purified heparinase. SDS-PAGE analysis of heparinase resulted an estimated molecular-weight of 42 kDa. It was also found that intracellular heparinase has the ability to depolymerize heparin to generate LMWHs. Further studies related to the mechanistic action, structural details, and genomics involved in heparinase production from Streptomyces variabilis are warranted for large scale production/purification optimization of heparinase for antithrombotic applications.

Bacterial secondary metabolites possess a wide range of biologically active compounds including antibacterial and antioxidants. In this study, a Gram-positive novel marine Actinobacteria was isolated from sea sediment which showed 84% 16S rRNA gene sequence (KT588655) similarity with Streptomyces variabilis (EU841661) and designated as Streptomyces variabilis RD-5. The genus Streptomyces is considered as a promising source of bioactive secondary metabolites. The isolated novel bacterial strain was characterized by antibacterial characteristics and antioxidant activities. The BIOLOG based analysis suggested that S. variabilis RD-5 utilized a wide range of substrates compared to the reference strain. The result is further supported by statistical analysis such as AWCD (average well color development), heat-map and PCA (principal component analysis). The whole cell fatty acid profiling showed the dominance of iso/anteiso branched C15–C17 long chain fatty acids. The identified strain S. variabilis RD-5 exhibited a broad spectrum of antibacterial activities for the Gram-negative bacteria (Escherichia coli NCIM 2065, Shigella boydii NCIM, Klebsiella pneumoniae, Enterobacter cloacae, Pseudomonas sp. NCIM 2200 and Salmonella enteritidis NCIM), and Gram-positive bacteria (Bacillus subtilis NCIM 2920 and Staphylococcus aureus MTCC 96). Extract of S. variabilis strain RD-5 showed 82.86 and 89% of 2,2-diphenyl-1-picrylhydrazyl (DPPH) free radical scavenging and metal chelating activity, respectively, at 5.0 mg/mL. While H2O2 scavenging activity was 74.5% at 0.05 mg/mL concentration. Furthermore, polyketide synthases (PKSs types I and II), an enzyme complex that produces polyketides, the encoding gene(s) detected in the strain RD-5 which may probably involve for the synthesis of antibacterial compound(s). In conclusion, a novel bacterial strain of Actinobacteria, isolated from the unexplored sea sediment of Alang, Gulf of Khambhat (Gujarat), India showed promising antibacterial activities. However, fractionation and further characterization of active compounds from S. variabilis RD-5 are needed for their optimum utilization toward antibacterial purposes.

Made available in DSpace on 2015-02-02T12:39:27Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-09-01Bitstream added on 2015-02-02T13:08:32Z : No. of bitstreams: 1 S1517-83822014000300022.pdf: 1163361 bytes, checksum: f6578eb61c12ca4b15b58b2bb5a98706 (MD5) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) The selection of new microorganisms able to produce antimicrobial compounds is hoped for to reduce their production costs and the side effects caused by synthetic drugs. Clavulanic acid is a β-lactam antibiotic produced by submerged culture, which is widely used in medicine as a powerful inhibitor of β-lactamases, enzymes produced by bacteria resistant to antibiotics such penicillin and cephalosporin. The purpose of this work was to select the best clavulanic acid producer among strains of Streptomyces belonging to the Microorganism Collection of the Department of Antibiotics of the Federal University of Pernambuco (DAUFPE). Initially, the strains were studied for their capacity to inhibit the action of β-lactamases produced by Klebsiella aerogenes ATCC 15380. From these results, five strains were selected to investigate the batch kinetics of growth and clavulanic acid production in submerged culture carried out in flasks. The results were compared with the ones obtained by Streptomyces clavuligerus ATCC 27064 selected as a control strain. The best clavulanic acid producer was Streptomyces DAUFPE 3060, molecularly identified as Streptomyces variabilis, which increased the clavulanic acid production by 28% compared to the control strain. This work contributes to the enlargement of knowledge on new Streptomyces wild strains able to produce clavulanic acid by submerged culture. Universidade Federal Rural de Pernambuco Departamento de Morfologia e Fisiologia Animal Universidade Estadual Paulista Júlio de Mesquita Filho Escola de Ciências Farmacêuticas Departamento de Bioprocessos e Biotecnologia Universidade Federal de Pernambuco Department of Antibiotics Universidade Federal de Pernambuco Laboratorio de Biotecnologia University of Genoa Department of Civil, Chemical and Environmental Engineering Universidade de São Paulo Departamento de Bioquimica e Tecnologia Farmacêutica Universidade Estadual Paulista Júlio de Mesquita Filho Escola de Ciências Farmacêuticas Departamento de Bioprocessos e Biotecnologia

INTRODUCTION Among various ecological habitats, soil is one of the richest reservoirs supporting a variety of organisms including microorganisms. Rhizosphere is the region of soil present in vicinity to plant roots and is influenced by secretions of plant roots called root exudates. This region is thought to be of great importance to plant health and soil fertility. The exudates from plant roots stimulate the growth of microbial populations in soil and thus, the microbial activity is greatest in rhizosphere region. Actinomycetes forms a key part of soil microorganisms. The species of the genus Streptomyces are saprophytic and are commonly associated with soils. It has been found that about 90 % of soil actinomycetes are reported to be Streptomyces species. In soil, Streptomyces species significantly contribute to the turnover of complex biopolymers such as cellulose, pectin, lignin etc. They are noteworthy as they are the prolific producers to a range of bioactive metabolites including antibiotics. Western Ghats of India covers an area of 1, 80, 000 km and represent just under 6 % of the land area of India. The area represents > 30 % of all plant, fish, herpeto-fauna, birds and mammal species found in India which include some of the globally threatened species. Agumbe, a region of Western Ghats of Shivamogga district, Karnataka, India is shown to be a rich reservoir for Streptomyces species having potent industrial and agricultural significance in terms of production of bioactive metabolites. Streptomyces species from Agumbe region of Western Ghats have shown to antimicrobial, antioxidant, enzyme inhibitory, insecticidal, cytotoxic, anthelmintic, analgesic, antiinflammatory, CNS depressant and antipyretic activities. Streptomyces variabilis strain PO-178 (Figure 1) of this study was isolated from a rhizosphere soil of Agumbe, Karnataka, India. The extract from this strain was shown to possess antimicrobial, insecticidal, cytotoxic, analgesic, antiinflammatory, antipyretic and CNS depressant activity. In continuation part of our previous study, the present study was conducted with an aim of determining antioxidant, anthelmintic and enzyme inhibitory activity of butanol extract of S.variabilis PO-178 isolated from rhizosphere soil of Agumbe, Karnataka, India.

Marine microorganism was emerging as the great source for the discovery of novel enzyme. The search and discovery of new enzymes derived from actinomycetes have received much attention nowadays due to a growing need for applications in various industries including food industry. Endo-β-1,4-xylanases is considered one of critical enzyme involves in the degradation of xylan that is able to cleave the β-1,4-glycosidic linkages in the xylan backbone resulting in various xylooligosaccharides and xylose. Screening and characterization of novel actinomycetes that is capable of producing high xylanase are necessary to produce xylooligosaccharides from hemicellulose hydrolysis process. The objective of this research is screening and characterizing of novel marine actinomycetes from working culture of Research Center for Biotechnology, Biotechnology Culture Collection (BTCC) that are capable of producing high-level hemicellulase-degrading enzymes, especially endo-xylanase enzyme. Approximately, 70 strains from Indonesia marine Actinomycetes have been screened by using congo red, SDS-PAGE and zymogram methods. Of these 70 strains, 3 strains were successfully identified that is capable in producing high level of xylanase enzymes based on the diameter of clear zone more than 1.5 cm on xylan plate medium pH 5.0 and 6.0. Three strains from marine Actinomycetes were identified based on analysis a 16S rRNA gene sequence revealed that all of strains belonging to the genus Streptomyces. Strain 47 is closely related with Streptomyces variabilis (98%). All strains had ability to produce xylanase at optimum pH 5.0 and temperature range between 50-60 °C with range activity from 2.5 – 4.3 U/mL. Each isolate had a molecular weight from 20-50 kDa based on SDS-PAGE and zymogram analysis. Based on TLC analysis using beechwood xylan, each isolate had ability to produce xylooligosaccharides. These characterizations showed that these isolates are potentially used for xylooligosaccharides productions. Strain 47 was selected for the next analysis for molecular cloning based on the pattern and results of TLC clearer then strain 41 and strain 42.

Out of 210 actinomycetes isolates belonged to the genus Streptomyces recovered from rhizospheric soil of Triticum vulgaris, Zea mays and Vicia faba cultivated in Assuit and New Valley Governorates of Egypt, ten isolates were capable of producing high amounts of L-glutaminase enzyme. The most potent L-glutaminase producer isolate was Streptomyces sp. ASU319 recovered from rhizosphere of Triticum vulgaris. The higher producer actinomycete isolate was identified by sequencing of 16S rRNA as Streptomyces variabilis ASU319 and was deposited in the GenBank nucleotide sequence database under accession number KC145278. Factors affecting L-glutaminase production by the Streptomyces variabilis ASU319(KC145278) were examined and the results revealed that the maximum L-glutaminase value was obtained when the isolate cultivated in the production broth medium supplemented by glutamine 8 mg/ml, adjusted at pH 4 and incubated at 35 °C. These results suggest that L-glutaminase-producing Streptomyces variabilis ASU319 could be used as a plant growth promoting rhizobacteria by increasing the ammonia content in the rhizosphere soil across degradation of the agricultural wastes. Also this isolate can be used in both pharmaceutical and food industrial application for L-glutaminase production on commercial scale.

Ammosamides E-F (1-2), are amidine analogs of the ammosamide family of alkaloids isolated from a marine-derived Streptomyces variabilis. Further studies with S. variabilis revealed a variety of aryl and alkyl amines added into the fermentation media could be efficiently incorporated into the ammosamide framework to generate a library of precursor-directed amidine analogs, ammosamides G-P (9 - 18). We demonstrate that the amines are introduced via non-enzymatic addition to the iminium ion of ammosamide C. Biological evaluation of the amidine analogs against quinone reductase 2 (QR2) showed low nM potency for a number of analogs. When tested for in vivo activity against a panel of non-small cell lung cancer (NSCLC) cell-lines there was a clear increase in potency by incorporation of lipophilic alkylamines, with the most potent compounds having sub μM IC(50) values (0.4 to 0.8 μM).

The search for novel bioactive compounds from the natural environment has been rapidly increased with the increase in multi-drug resistant (MDR) pathogens. In the present study, the antimicrobial potential of novel actinomycetes has been evaluated by initial screening of six soil samples. Primary and secondary screening was performed against Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Candida albicans, Candida tropicalis, Trichophyton rubrum, and other MDR bacterial and fungal test strains, and at the end thirteen active isolates were selected for further study. Microbial strains were identified on the basis of growth conditions and other biochemical characters. Five most active microbial strains were identified using 16S rRNA sequence homology and designated as Streptomyces xanthophaeus MTCC 11938, Streptomyces variabilis MTCC 12266, Streptomyces xanthochromogenes MTCC 11937, Streptomyces levis EU 124569 and Streptomyces sp. NCIM 5500. Four antibacterial and three antifungal compounds isolated from the above five isolates were purified and partially characterized using UV absorption and IR spectra. Two antibacterial metabolites, belong to chromone and peptide antibiotic, respectively. The antifungal compounds were found to be of non-polyene nature. In conclusion, we study the isolation of novel bacterial strains of actinomycetes for producing novel compounds having antibacterial and antifungal activities from the unexplored agro-ecological niches of India. Also, this study paves the way for further characterization of these isolates of Streptomyces sp. for their optimum utilization for antimicrobial purposes.

A Gram-positive, aerobic, non-motile actinomycete (strain MS 3/20T) was isolated from the sediment of the Sundarbans mangrove forest in India. On International Streptomyces Project (ISP) medium 2, the isolate produced yellowish brown to red aerial hyphae that carried spiny-surfaced spores in a retinaculum-apertum arrangement. Whole-cell hydrolysate of the strain contained LL-diaminopimelic acid and galactose. Predominant menaquinones were MK-9(H8) and MK-9(H6). Diagnostic polar lipids were glycolipid, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylcholine, unidentified phospholipid and unidentified amino lipid. The major fatty acids were anteiso-C15:0 (17.53%), iso-C16:0 (23.89%) and anteiso-C17:0 (10.29%). The strain showed 100% 16S ribosomal RNA (rRNA) gene sequence similarity with Streptomyces variabilis NBRC 12825T, Streptomyces erythrogriseus LMG 19406T, Streptomyces griseoincarnatus LMG 19316T and Streptomyces labedae NBRC 15864T. However, strain MS 3/20T could be distinguished from these and seven other closely related species based on low levels of DNA-DNA relatedness (27.2-53.8%), supported by the unique banding pattern obtained from random amplified polymorphic DNA-PCR amplification and the distinctive matrix-assisted laser desorption/ionization-time-of-flight/mass spectrometry (MALDI-TOF/MS) profile of whole-cell proteins acquired for strain MS 3/20T in comparison with its phylogenetic relatives. Disparate morphological, physiological and chemotaxonomic features, principally growth in NaCl, further corroborated the distinction of strain MS 3/20T from other phylogenetic relatives. Strain MS 3/20T is therefore suggested to be a novel species of the genus Streptomyces, for which the name Streptomyces euryhalinus sp. nov. is proposed. The type strain is MS 3/20T (=CICC 11032T=DSM 103378T).

Ammosamide D (1), an oxidized analog of the ammosamide family, was isolated from a marine-derived Streptomyces variabilis. Pyrroloquinoline containing alkaloids are a growing class of natural products, with 1 being the first example of an oxidized analog resulting in a 5,6-dioxo-5,6-dihydroquinoline ring system. Attempts at chemical conversion of ammosamide B to ammosamide D revealed that a strong chemical oxidant is required. Ammosamide D has modest cytotoxicity to the MIA PaCa-2 pancreatic cancer cell line.

Objective: This study was focused on an evaluation of antimicrobial activity of actinobacterial isolated from Kanyakumari marine sediments.Methods: This study includes sample collection from Kanyakumari beach, followed by isolation of marine actinobacteria, screening for antibacterial activity and antifungal activity. Finally, the most active isolate was identified using 16S rRNA sequencing. Results: Marine actinobacteria are one of the leading microbes of the ocean known for producing excellent secondary metabolites and having a broad spectrum of anti-microbial activity, hence they are very important from an industrial point of view. The marine sediment sample used was collected from Kanyakumari beach, in the month of July, falling in the latitudinal range of 8.5074°N and in the longitude of 76.9730°E. A total of 8 actinobacterial colonies were isolated by spread plate technique on Actinomycetes isolation agar, Kuster's agar and Starch casein agar. The isolate cultures were designated as UST1- UST8. Among them, UST3 showed a maximum zone of inhibition against clinical pathogens Salmonella typhi and Aspergillus niger with a zone of inhibition of 22mm and 20mm respectively. In solvent extraction study ethyl acetate and hexane was found as best solvents for extraction. Potential isolate UST3 was identified as Streptomyces variabilis using morphological studies and 16S rRNA sequencing. Potential strain was submitted as Streptomyces variabilis- VITUMVB03Conclusion: Results obtained in this study concluded that marine actinobacteria have broad-spectrum antimicrobial activity and can be used in the pharmaceutical industry.Keywords: Anti-fungal activity, Anti-bacterial activity, Salmonella typhi, Aspergillus niger, Streptomyces variabilis

Since the marine environmental conditions are extremely different from the other ones, marine actinomycetes might produce novel bioactive compounds. Therefore, actinomycete strains were screened from marine water and sediment samples collected from the coastal areas of Northern Vietnam. Ninety-nine actinomycete strains were obtained on starch-casein agar media by dilution technique, only seven strains, named HP112, HP12, HP411, HPN11, HP 11, HPT13 and HPX12, showed significant antibacterial activity against both gram-positive and gram-negative bacteria (Bacillus subtilis ATCC 6633, Staphylococcus epidemidis ATCC 12228, Escherichia coli ATCC 11105). Further studies were carried out with the most active HP411 strain against Candida albicans ATCC 10231. This strain could grow rapidly on starch casein agar and other media with high salt containing 7-10% NaCl at 28-30oC. Spore-chain of HP411 showed an elongated and circular shape with 10 to 30 spores/chain. Identification of the strain was carried out by employing the taxonomical studies including the 16S rRNA sequence. Based on phylogenetic and phenotypic evidence it is proposed that HP411 to be belongs to species Streptomyces variabilis. The potent of the crude extract of fermentation broth of HP411 that are effective against wide range of pathogens: both grampositive, gram-negative and fungi. Further studies revealed that the crude extract HP411 could obtain the anticancer activity for cancer cell lines: Hep-G2 (liver cancer cell line); RD (cardiac and skeletal muscle letters cell line); FL (membrane of the uterus cancer cell line). However, the actinomycetes from marine ecosystem will be useful for the discovery of new drugs in the future.

Objective: This study was aimed to evaluate the bioactive potential (antimicrobial and antioxidant) of marine actinobacteria isolated from Thottadamarine sediment, Kannur, Kerala.Methods: The study involved isolation of marine actinobacteria from Thottada marine sediments, followed by antimicrobial and antioxidant activityof the crude extract. Finally, identification of potential isolates.Results: In this study, a total of 6 actinobacterial colonies were isolated, out of which only one isolate DV-35 showed maximum anti-microbial andanti-oxidant activity. The isolate DV-35 showed maximum inhibitory activity against Gram-negative bacterial pathogens Pseudomonas aeruginosa(18 mm) followed by Salmonella typhi (17 mm) and Klebsiella sp. (13 mm) at a dose of 100 μg/ml. In antifungal activity, extract showed maximumactivity against Aspergillus niger (19 mm) followed Aspergillus flavus (17 mm) at a dose of 100 μg/ml. Simultaneously the extract was evaluated for itsantioxidant activity. The potential isolate DV-35 also showed moderately higher antioxidant activity in various screening assay, viz., 2,2-diphenyl-1-picrylhydrazyl scavenging assay (80.12%), metal chelating assay and reducing power assay (76%) at a concentration of 100 μg/ml. Potential isolateDV-35 was identified as Streptomyces variabilis DV-35 using molecular 16S rRNA sequencing.Conclusion: The results obtained suggest that the extract is having bioactive metabolites that can be considered as a potential source for antimicrobialand anti-oxidant drug development.Keywords: Marine actinomycetes, Anti-microbial activity, Anti-oxidant activity, Pseudomonas aeruginosa, Aspergillus niger, Streptomyces variabilis.

A culture similar to Streptomyces variabilis was found to produce a novel cyclic hexadepsipeptide antibiotic named variapeptin. Variapeptin is structurally related to azinothricin, A83586C, and citropeptin. The antibiotic was active against Gram-positive bacteria and showed cytotoxic activity against mammalian cells.

In the present study, characterization and antibacterial activity of a glycoside antibiotic from fermentation broth of bioactive Streptomyces variabilis PO-178 recovered previously from Western Ghat soil of Agumbe, Karnataka, India was investigated. Mass cultivation of the strain PO-178 was carried out in Starch casein nitrate broth. The fermentation broth was extracted using butanol solvent in a separation funnel. The concentrated butanol extract was subjected to chromatographic techniques viz., thin layer and silica gel column chromatography for purification of bioactive components. Out of 3 fractions (A, B and C) obtained, only one fraction (C) displayed inhibitory activity against Staphylococcus aureus and Pseudomonas aeruginosa. The bioactive fraction C was subjected to spectral analysis (LC-MS, IR, 1 H-NMR and 13 C-NMR) in order to determine the structure. On the basis result of spectral analysis, the purified fraction was predicted as a glycoside antibiotic with molecular weight 514 and molecular formula C 24 H 34 O 12 . The antibiotic displayed marked inhibitory activity against S. aureus as revealed by wider zones of inhibition and low minimum inhibitory concentration value.

Variapeptin and citropeptin were found as novel hexadepsipeptide antibiotics produced by Streptomyces variabilis and Streptomyces flavidovirens, respectively. Their structures were elucidated by NMR spectral analysis including a variety of 2D techniques. Variapeptin and citropeptin are structurally related to azinothricin and A83586C, respectively.

espanolEl presente trabajo tiene como objetivos evaluar actinomicetos aislados de Argopecten purpuratus y su capacidad de producir enzimas extracelulares (EEC), asi como determinar su actividad antagonista frente a patogenos de importancia en acuicultura. Se aislaron 27 cepas de actinomicetos a partir de la masa visceral de especimenes adultos de A. purpuratus colectados en la localidad de Pisco y Pucusana (Lima) - Peru. El 81,5 y 59,2% de los aislados mostraron actividad proteolitica y lipolitica, respectivamente. Asimismo, las cepas senaladas como ARG 9-II, ARG 10-II, ARG 12-II y ARG 14-II mostraron mayor actividad antimicrobiana contra los patogenos Vibrio anguillarum, V. vulnificus, V. alginolitycus, Lactococcus garvieae, Streptococcus iniae, Carnobacterium piscicola y Yersinia ruckeri. La cepa ARG 4-II exhibio la mayor actividad inhibitoria. La Concentracion Minima Inhibitoria (CMI) del extracto diclorometanico de la cepa ARG 12-II frente a V. anguillarum y V. alginolyticus fue calculada en 250 y 500 µg ml-1 respectivamente. Las cepas ARG 9-II, ARG 12-II y ARG 14-II sobre la base del analisis de su ARNr 16S fueron identificadas como Streptomyces variabilis, St. labedae y St. rochei, respectivamente. Los resultados senalan a A. purpuratus como una fuente promisoria de aislamiento de nuevas cepas de Streptomyces con alta capacidad bioactiva y antagonista contra patogenos de importancia en acuicultura y con posibilidades de ser desarrolladas como potenciales agentes probioticos en el futuro. EnglishThe present study was aimed at isolating Argopecten purpuratus-associated actinomycetes strains, and evaluating their capacity of production of extracellular enzymes (ECE), as well as inhibitory compounds against relevant pathogens in commercial aquaculture. Twenty seven strains were isolated from the gut of A. purpuratus adult specimens that were collected in the city of Pisco and Pucusana (Lima) _ Peru; 81.5 and 59.2% of the isolates showed proteolytic and lipolytic activity, respectively. In addition, the strains ARG 9-II, ARG 10-II, ARG 12-II and ARG14-II evidenced broad-spectrum antimicrobial activity against the pathogens Vibrio anguillarum, V. vulnificus, V. alginolitycus, Lactococcus garvieae, Streptococcus iniae, Carnobacterium piscicola, and Yersinia ruckeri. The strain ARG 4-II produced the highest inhibitory effect against S. iniae. The Minimum Inhibitory Concentration (MIC) of the dichloromethane extract obtained from the strain ARG 12-II supernatant was 250 and 500 µg ml-1 against V. anguillarum and V. alginolyticus, respectively. Based on 16S rRNA sequence analysis, strains ARG 9-II, ARG 12-II and ARG 14-II were identified as Streptomyces variabilis, St. labedae and St. rochei, respectively. Results indicate that A. purpuratus is a promissory source for the isolation of new strains of Streptomyces with high bioactivity and antagonistic capacity against relevant pathogens in aquaculture. These strains have high potential for being developed as probiotic agents in the future.