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Comparative tests on the sensitivity of actinomycetes to cadmium and copper ions were carried out on 19 wild strains of the genus Streptomyces. The strains were tested by placing solutions of cadmium chloride on filter paper disks in quantities of 20 and 40 μg Cd2+, and also 20, 40 and 80 μg Cu2+ converted to metal. Both conidial and vegetative forms of actinomycetes were used as inoculum. Differentiation was found in the reactions of the actinomycetes on the tested metals depending on the nutrient used, especially on nitrogen sources. Copper ions have a greater effect on the vegetative forms of these organisms than cadmium ions, while cadmium ions exert an inhibiting effect on the process of conidia germination.
In this study, about 112 isolates of Streptomyces were isolated from chickpea rhizospheric soils. Among the isolated strains, five showed strong inhibitory effects against chickpea Fusarium wilt caused by Fusarium oxysporum f. sp. ciceris in vitro using plate assay and selected for further studies. The selected strains were identified as Streptomyces spp. based on morphological and biochemical characterization as well as 16S rDNA sequences analysis. Our results assigned them to strains related to genus of Streptomyces. In vitro, antagonistic effects of Streptomyces strains against the disease were evaluated through the dual-culture method, volatile and non-volatile metabolites, siderophore, protease and chitinase production. All bacterial strains inhibited mycelial growth of the pathogen ranging from 26 to 44.2% in dual culture assay. The non-volatile extract of five of the Streptomyces strains inhibited more than 50% growth of the pathogen, whereas volatile compounds were less effective on mycelial growth inhibition (20.2 to 33.4%). The ability of the biocontrol agents to produce siderophore and protease were varied, whereas, production of chitinase was detected for all strains. Results of the greenhouse assay indicated that all biocontrol agents reduced disease severity (ranging from 38.7 to 54.8%). Accordingly, strain KS62 showed higher control efficacy (54.8%). In addition, the biomass of chickpea plants (plant height and dry weight) significantly increased in plants treated with Streptomyces strains compared to non-bacterized control. The results of this study showed that it may be possible to manage chickpea Fusarium wilt disease effectively by using Streptomyces species, as biocontrol agents. Therefore, evaluating their efficiency under field conditions is needed.
The purpose of this study was to determine the influence of growth conditions and medium composition on the production of chitinase by Strtptomyces sp. (strain S₂₄₂,). Production of chitinase by strain S₂₄₂ was detected on colloidal chitin agar (CCA) medium after 8 days of incubation at 28°C resulting in a clear zone 10 mm around the colony. Chitinase activity was assayed as the amount of N-acetylglucosamine released in pmol/ml/min using the dinitrosalicylic acid assay method. The crude enzyme had maximum activity (0.162 U ml/l) after 4 days of incubation at pH 7 and 30°C when the broth medium was supplemented with 1.6% of colloidal chitin. However, enzyme activity was strongly decreased at 40°C and extreme acidic and alkaline pH values. SDS-PAGE and zymogram analysis revealed six distinctive bands that range from 39 to 97 kDa with chitinolytic activity. The findings of this investigation create a possibility for the use of the organism in the commercial production of chitinase. In addition, it can be a source of DNA for cloning the chitinase gene(s) to generate phytopathogen resistant transgenic plants.
A thermo tolerant, feather-degrading, newly isolated actinobacterial strain Streptomyces minutiscleroticus DNA38 was investigated for its ability to produce keratinase. Maximum production (283.4 IU) of keratinase by Streptomyces minutiscleroticus DNA38 in starch chicken feathers medium under submerged bioprocess was observed at optimized conditions of pH 9.0 of the medium and 45 °C incubation temperature. Further, an enhanced production (435.8 IU) of keratinase was achieved employing response surface methodology. Combined interactive effect of starch (7.50 g/L), yeast extract (0.74 g/L) and chicken feathers (7.50 g/L) were found to be the critical process variables for enhanced production under central composite design. Chicken feathers showed a direct action and addition of starch and yeast extract to the medium proved effective for a significant increase in the production of keratinase. The purified keratinase was monomeric and had a molecular mass of 29 kDa. The enzyme activity was significantly inhibited after pH 9.0 and temperature 50 °C.
The use of microbial exopolysaccharides (EPS) in the food, pharmaceutical, and chemical industries has steadily increased during the past decade. A bioactive EPS producing microorganism, Streptomyces nasri was isolated from Kuwait tropical soil and the proteopolysaccharide was tested for its antimicrobial activity. The isolate was subjected to ultraviolet (UV) radiation and acridine orange (AO) treatment to select for superior proteopolysaccharide producers. Among eight (five derived from UV exposure and three from AO exposure) morphological variants of Streptomyces nasri, two mutants showed increased EPS production, from 1.8 g/l to 2.3 g/l. The SDS-PAGE profiles of exopolysaccharides were determined. The molecular weight of the proteopolysaccharide ranged from 18 to 200 kDa. Mutants derived from UV exposure produced polysaccharides with higher molecular weight than those derived from acridine orange exposure. Acridine orange derived mutants produced lower molecular weight polysaccharides. Culture super-natants have been partially characterized and they show antimicrobial activity against a wide range of microorganisms. The structure of the exopolysaccharide was determined using NMR spectroscopy. The polysaccharide was also tested for cytotoxic activity against human brain tumor cell line using SRB assay.
Celem badań było określenie wybranych właściwości enzymatycznych (amylolitycznych, celulolitycznych, chitynolitycznych, pektynolitycznych, proteolitycznych) i zdolności rozpuszczania Ca3(PO4)2 promieniowców z rodzaju Streptomyces wyizolowanych z gleby i ryzosfery ziemniaka. Na podstawie wielkości stref hydrolizy badanych substratów będących następstwem reakcji enzymatycznych stwierdzono, że testowane szczepy Streptomyces wykazały się wysoką aktywnością enzymatyczną. Najwięcej szczepów wykorzystywało jako źródło węgla skrobię, a następnie celulozę (na podłożu CMC-Na) i żelatynę. Najmniej izolatów korzystało z pektyn na podłożu o pH 5,2 oraz z celulozy w formie sproszkowanej. Wytwarzanie chitynaz u wszystkich badanych promieniowców było dość powszechne (75 %), podobnie jak zdolność rozpuszczania Ca3(PO4)2 (70 % szczepów).
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