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dc.contributor.advisorSmith, Valerie J.
dc.contributor.authorDesbois, Andrew Paul
dc.description.abstractThe aim of this thesis was to isolate the compounds responsible for the antibacterial activity of cell extracts of the marine diatom, Phaeodactylum tricornutum. Marine microalgae are not only important primary producers but, due to their phylogenetic diversity, they are also a potential source of novel bioactive compounds. The marine diatom, P. tricornutum, was selected for study because its cell extracts are known to be antibacterial but the compounds responsible have not been isolated. In this thesis, the compounds responsible for the antibacterial activity are isolated from aqueous methanol P. tricornutum cell extracts by column chromatography and reverse phase high-performance liquid chromatography using a bioassay-guided approach. The compounds in three active fractions were identified by mass spectrometry and nuclear magnetic resonance spectroscopy as the unsaturated fatty acids (5Z, 8Z, 11Z, 14Z, 17Z)-eicosapentaenoic acid, (9Z)-hexadecenoic acid and (6Z, 9Z, 12Z)-hexadecatrienoic acid. The fatty acids were found to be antibacterial against Staphylococcus aureus at micromolar concentrations. P. tricornutum exists in different cell morphs and, interestingly, extracts prepared from cultures in the fusiform morph were found to have greater antibacterial activity than extracts from oval cultures. This is explained by greater levels of the three antibacterial fatty acids in the fusiform cell extracts. The antibacterial fatty acids are proposed to be released by enzyme action when the diatom cells lose their integrity. The release of free fatty acids by diatoms is suggested to be a simple, very low cost population-level activated defence mechanism against potential pathogenic bacteria triggered when the cell loses its integrity. Further, this pathway may act against multiple threats to the microalga, including grazers, as fatty acids exhibit activity in diverse biological assays. Finally, whilst two of the fatty acids, (9Z)-hexadecenoic acid and (5Z, 8Z, 11Z, 14Z, 17Z)-eicosapentaenoic acid, inhibited the growth of MRSA their usefulness as therapeutic compounds may be limited due to their instability and their broad biological activity.en
dc.format.extent2675 bytes
dc.publisherUniversity of St Andrews
dc.rightsCreative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported
dc.subjectNatural productsen
dc.subjectDrug resistanceen
dc.subjectEicosapentaenoic aciden
dc.subjectPalmitoleic aciden
dc.subjectHexadecatrienoic aciden
dc.subjectMultidrug-resistant Staphylococcus aureusen
dc.subjectChemical ecologyen
dc.titleAntibacterial free fatty acids from the marine diatom, Phaeodactylum tricornutumen
dc.contributor.sponsorBiotechnology and Biological Sciences Research Council (BBSRC)en
dc.contributor.sponsorAquapharm Bio-Discovery Ltd.en
dc.type.qualificationnamePhD Doctor of Philosophyen
dc.publisher.institutionThe University of St Andrewsen

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Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported
Except where otherwise noted within the work, this item's licence for re-use is described as Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported