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- Marine natural products and brown macroalga cystophora moniliformis chemistry
Ghandourah, Mohammed Ali H.
- University of Newcastle. Faculty of Science & Information Technology, School of Environmental and Life Sciences
- Research Doctorate - Doctor of Philosophy (PhD)
- Chemists have isolated and identified many diverse natural products from both terrestrial and marine organisms. The fascinating structural peculiarities and unusual molecular arrangements of many marine compounds have made the field of marine natural products particularly attractive. In the marine natural products group at The University of Newcastle our research is focussed on the identification of new compounds and, in addition, investigation of chemotaxonomy and ecological chemistry. Much of our work is involved with the marine brown algae of the genus Cystophora which consists of about 20 species endemic to Australasian waters, from the western coast of Australia around to the southeast to Newcastle, including Tasmanian and New Zealand waters. The marine brown algae that was the focus of this research is Cystophora moniliformis, which has a wide distribution across southern Australia. Sixteen secondary metabolites were isolated from C. moniliformis. Fifteen had been previously identified (18, 19, 21, 23-32, 34 and 37). Compound 42 is a new linear terpenoid belonging to the same farnesylacetone family as the other metabolites and possess an unusual quaternary aldehyde functionality. [Figures could not be replicated]. The secondary metabolites of algae potentially have roles such as in allelopathic interactions or as herbivore feeding deterrents. Geranylacetone, a metabolite isolated from a South Australian collection of C. moniliformis was found to act as a feeding deterrent towards the sea urchin Tripneustes gratilla. The concentration of secondary metabolites in the marine ecosystem may be affected by herbivore interactions and seasonal variations. We were interested in seeing whether secondary metabolite production varied in response to the presence of herbivores (and/or the level of herbivory), however, before commencing this study we had to establish the baseline variability of secondary metabolite concentrations throughout the year. Algae were sampled monthly for just over one year and crude extracts examined by gas chromatography - mass spectrometry. We have been able to show that the concentration of the major secondary metabolites generally vary regularly with the seasons, but superimposed on this, there are smaller scale variations, which have significant implications on how the metabolites interact with each other, due to their order of biosynthesis and in response to environmental factors and events. The secondary metabolites could be divided into three groups, those that showed maximum production close to the time of maximum algal metabolic production in late summer, a second that peaked much later, in winter, and the third group which contains "the others" - compounds that peaked somewhere in between the first two groups or showed unique fluctuations in their compound concentration profile. It appears that the biosynthesis of the first group may be quite sensitive to water temperature, whereas the second group are less so. The possible implications of the significance of a compound belonging to the third group is discussed. In one case, the compound may be misplaced (and should be in the second group), perhaps due to limitations in the analysis, while others may be compounds that have responded to environmental or ecological events not measured in this study. Water temperature appears to show the closest association with metabolite production, especially compounds falling in the first group of secondary metabolites and primary metabolism in general. What was especially interesting is that it appears that sudden precipitation events can affect metabolite production by causing changes in water temperature. We conclude that to gain a proper understanding of the details of marine ecosystems and the factors that affect them, purely observational studies of an ecosystem should include as many environmental, chemical and biological variables as possible, so that cause and effect is not mis-attributed as it may be in more limited studies. These can subsequently be confirmed by the sue of well designed and executed manipulative experiments which will allow unambiguous assignment of 'cause and effect'.
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- Copyright 2012 Mohammed Ali H. Ghandourah