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close this section of the library Marine metabolites -- Solomon Islands


View the PDF document Bioactive secondary metabolites from culturable unusual actinomycetes from Solomon Islands marine sediments : isolation and characterization of bioactive compounds
Author: Singh, Ahilya
Institution: University of the South Pacific.
Award: M.Sc.
Subject: Actinobacteria -- Solomon Islands, Marine metabolites -- Solomon Islands, Microbial metabolites -- Solomon Islands
Date: 2014
Call No.: Pac QR 82 .A35 S56 2014
BRN: 1201029
Copyright:Under 10% of this thesis may be copied without the authors written permission

Abstract: A total of 37 actinomycete strains were purified from 25 Solomon Islands marine sediments using four different types of isolation media. Among them, 54% of the strains had obligate requirement of seawater for growth. The ethyl acetate extract of 100 ml fermentation product of each strain was screened for antimicrobial activity against multidrug resistant human pathogens and cytotoxic activity against brine shrimps. A total of 67% of the ethyl acetate extracts showed antimicrobial and/or cytotoxic activities. A strain F-1915 was selected for isolation and evaluation of bioactive compound(s) based on its bioactive properties and chemical profile analysis using the LC-MS. The strain F-1915 was identified to have 96% sequence similarity to Streptomyces violaceusniger on the basis of 16S rDNA sequences using BLAST analysis. The 16S rDNA revealed that the strain F-1915 is a new member of MAR4 clade of actinomycetes. The MAR4 clade is an interesting clade of actinomycetes known for the production of pharmaceutically important hybrid isoprenoid compounds. The ethyl acetate extract of the fermentation product of this strain was purified by silica gel column chromatography and afforded the isolation of one bioactive pure compound. Based on the 1D and 2D NMR spectral data of compound 1 it was identified as a new mono-brominated phenazinone, Marinophenazimycin A, a structure which has already been studied by external collaborators at Scripps Institution of Oceanography but is yet to be published. Compound 1 displayed significant antimicrobial activity against drug resistant human pathogens. The minimum inhibitory concentration (MIC) of compound 1 was against Methicillin Resistant Staphylococcus aureus (MRSA) was about 1.9 μg/ml and MIC recorded against Amphotericin Resistant Candida albicans (ARCA) was about 0.24 μg/ml. The bioactivity of compound 1 against ARCA was found to be better than the standard antifungal agent amphotericin B. Compound 1 however did not show any cytotoxic activity against brine shrimps.
View the PDF document Extraction, isolation, purification and characterization of bioactive compounds from the marine sponge Melophlus sp.
Author: Prasad, Pritesh.
Institution: University of the South Pacific.
Award: M.Sc.
Subject: Marine metabolites -- Solomon Islands , Sponges -- Microbiology -- Solomon Islands , Bioactive compounds , Extraction (Chemistry)
Date: 2011.
Call No.: Pac QP 632 .M37 P7372 2011
BRN: 1182805
Copyright:Under 10% of this thesis may be copied without the authors written permission

Abstract: This thesis describes the isolation and structural elucidation of bioactive compounds from a marine sponge of genus Melophlus collected from the Solomon Islands. The sponge under investigation belongs to the family Ancorinidae under the order Astrophorida. Screening of the crude extract for anti-microbial activity against methicillin resistant Staphylococcus aureas, wild type Staphylococcus aureas, vancomycin resistant Enterococcus faecium, wild type Candida albicans and amphotericin resistant Candida albicans was carried out. In addition, cytotoxicity was checked using the brine shrimp assay. Preliminary bioassay results showed that the crude extract exhibited anti-candida activity as well as cytotoxic properties. Bioassay guided fractionation utilising isolation techniques such as solvent-solvent partitioning, vacuum liquid chromatography, flash column chromatography together with purification by semi-preparative HPLC resulted in the discovery of four cytotoxic compounds. Two known cyclic depsipeptides termed papuamides C (compound III) and D (compound I) together with the new analogues designated as papuamide E (compound IV) and F (compound II) have been isolated from the marine sponge Melophlus sp. The structures were determined by interpretation of the spectroscopic data (1H-NMR, HSQC, 1H-1H COSY, HMBC and HSQC-TOCSY) and LC-MS analysis, as well as with reference to the literature available on papuamides A-D. Papuamides C-F contains 11 amino acid residues which includes glycine (two residues), alanine, threonine (two residues), 3-4-dimethylglutamine, - methoxytyrosine, 3-methoxyalanine, 2-amino-2-butenoic acid, 3-hydroxyleucine and homoproline residues. In addition, papuamides C-D contain 2,3-dihydroxy-2,6,8- trimethyldeca-4,6-dienoic acid moiety which has been substituted in papuamide E and F with a 3-hydroxy-2,6,8-trimethyldeca-4,6-dienoic acid moiety. Moreover, papuamides C-F have been found to be cytotoxic with lethal dosage (LD50) values of 92ppm, 92ppm, 104ppm and 106ppm respectively. This is the first report documenting the LD50 of the known compounds papuamides C-D and the isolation of new analogues, papuamide E and F. This is also the first report stating the isolation of depsipeptides, papuamides C-F, from a marine sponge of the genus Melophlus.
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