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Scholarly Works (3 results)

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Research Theses and Dissertations (1997)

Research results described here are from experiments conducted in organic chemistry and marine microbiology. Sponge derived chemistry has provided the marine natural products field with a higher percentage of bioactive leads than temstrial plants or microorganisms. Inspection of these bioactive leads reveals structure types that occur in more than one Demosponge or invertebrate species. It has been hypothesized that this trend indicates complex biosyntheses occmring which include microorganisms associated with the sponges. This theme built on circumstantial evidence is discussed first.

Initially we investigated jasplakinolide's occurrence from unrelated sponges including Jaspis aff. johnstoni. Fungi were cultured from this sponge to test the possibility of microorganism biosynthetic involvement. From an unidentified culture we discovered the coriolins, previously known from the temstrial fungus Coriolus consors, and new sesquiterpenes named the chloriolins. We tested the biosynthetic potential of C. consors by growing it in liquid broths with varied salt and fresh water media. We characterized a new coriolin type compound and new and known piperazine diones.

Fungi were cultured from the sponge Jaspis aff. coriacea including one strain identified as Aspergillus ochraceus. This fungus produced novel chlorinated polyketides named chlorocarolides which appear to have no ecological connection with sponge's known metabolites. However they do appear analogous to the known Aspergillus metabolite carotic acid. Relative stereochemistry of the chlorocarolides was solved by 1H NMR coupling and molecular modeling analysis.

Our fungi library isolated from sponge tissue provided culture extracts screened in two ways: for bioactivity using in-house and off-campus cancer-based bioassays, and for large molecular weight compounds using electrospray ionization mass spectrometry (ESIMS). Polyketides isolated include new nectriapyrones and the novel compound 14,15-secocurvularin. ESIMS results assisted our dereplication process of known compounds isolated.

We have shown sponges are a good source for isolating fungi cultures and these cultures may be extracted and purified to provide new and bioactive metabolites from polyketide, terpene, and polypeptide structure classes. Our results indicate that the culturable fungi do not influence the biosynthesis of sponges as once hypothesized and that other classes of microorganisms may merit investigation for their ability to influence sponge metabolite biosynthesis.

    Cover page: Investigations of Natural Products from Marine Sponge Derived Fungi
    • Article
    • Peer Reviewed
    UC Irvine Previously Published Works (2013)
    Although several per cent of net carbon assimilation can be re-released as isoprene emissions to the atmosphere by many tropical plants, much uncertainty remains regarding its biological significance. In a previous study, we detected emissions of isoprene and its oxidation products methyl vinyl ketone (MVK) and methacrolein (MACR) from tropical plants under high temperature/light stress, suggesting that isoprene is oxidized not only in the atmosphere but also within plants. However, a comprehensive analysis of the suite of isoprene oxidation products in plants has not been performed and production relationships with environmental stress have not been described. In this study, putative isoprene oxidation products from mango (Mangifera indica) branches under abiotic stress were first identified. High temperature/light and freeze-thaw treatments verified direct emissions of the isoprene oxidation products MVK and MACR together with the first observations of 3-methyl furan (3-MF) and 2-methyl-3-buten-2-ol (MBO) as putative novel isoprene oxidation products. Mechanical wounding also stimulated emissions of MVK and MACR. Photosynthesis under (13)CO2 resulted in rapid (<30 min) labelling of up to five carbon atoms of isoprene, with a similar labelling pattern observed in the putative oxidation products. These observations highlight the need to investigate further the mechanisms of isoprene oxidation within plants under stress and its biological and atmospheric significance.
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    Cover page: Emissions of putative isoprene oxidation products from mango branches under abiotic stress
    • Article
    • Peer Reviewed
    UC Berkeley Previously Published Works (2014)
    The volatile gas isoprene is emitted in teragrams per annum quantities from the terrestrial biosphere and exerts a large effect on atmospheric chemistry. Isoprene is made primarily from recently fixed photosynthate; however, alternate carbon sources play an important role, particularly when photosynthate is limiting. We examined the relative contribution of these alternate carbon sources under changes in light and temperature, the two environmental conditions that have the strongest influence over isoprene emission. Using a novel real-time analytical approach that allowed us to examine dynamic changes in carbon sources, we observed that relative contributions do not change as a function of light intensity. We found that the classical uncoupling of isoprene emission from net photosynthesis at elevated leaf temperatures is associated with an increased contribution of alternate carbon. We also observed a rapid compensatory response where alternate carbon sources compensated for transient decreases in recently fixed carbon during thermal ramping, thereby maintaining overall increases in isoprene production rates at high temperatures. Photorespiration is known to contribute to the decline in net photosynthesis at high leaf temperatures. A reduction in the temperature at which the contribution of alternate carbon sources increased was observed under photorespiratory conditions, while photosynthetic conditions increased this temperature. Feeding [2-(13)C]glycine (a photorespiratory intermediate) stimulated emissions of [(13)C1-5]isoprene and (13)CO2, supporting the possibility that photorespiration can provide an alternate source of carbon for isoprene synthesis. Our observations have important implications for establishing improved mechanistic predictions of isoprene emissions and primary carbon metabolism, particularly under the predicted increases in future global temperatures.
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