Doctor of Philosophy (PhD)
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biochemistry, cellular and molecular physiology, environmental chemistry, environmental health, marine biology, molecular biology
Date of Defense
The dinoflagellate Karenia brevis, blooms annually in the Gulf of Mexico, producing a suite of neurotoxins known as the brevetoxins. The cellular toxin content of K. brevis, however, is highly variable between or even within strains. I investigated biochemical differences between high (KbHT) and low (KbLT) toxin producing cultures both derived from the Wilson strain, related to energy-dependent quenching (qE) by photosystem II, and the content of reduced thiols of the proteome. By characterizing the xanthophyll content of the two strains I was able to determine that KbLT performs qE inconsistently. To investigate the source of the differences in qE, RT-qPCR was utilized to examine gene expression of the xanthophyll cycle enzyme diadinoxanthin de-epoxidase (Dde), however no differences in expression were found. Furthermore, using redox proteomics the protein expression of Dde and monogalactosyldiacylglycerol (MGDG) vii synthase were determined to not be significantly different in the two cultures. Also reported are significant differences in the lipidomes of KbHT and KbLT with respect to MGDG, which facilitates the xanthophyll cycle. Redox proteomics experiments detected a significantly higher proportion of proteinogenic cysteine thiols in the reduced thiol state in the low toxin proteome, including plastid localized thioredoxin (Trx), which can result in inactivation of Dde and activation of MGDG synthase. Moreover, recombinant K. brevis thioredoxin reductase (KbTrxR) was produced in order to characterize the interaction of this enzyme with brevetoxin. Brevetoxin was found to inhibit reductase activity towards various substrates. Using mass spectrometry, I was able to detect an adduct of KbTrxR and brevetoxin on a cysteine residue at the N-terminal redox center. This supports the hypothesis that brevetoxin could mediate redox homeostasis by interacting with thiol-disulfide centers in thioredoxin reductase
Previously Published In
Chen, W., Colon, R., Louda, J. W., del Rey, F. R., Durham, M., & Rein, K. S. (2018). Brevetoxin (PbTx-2) influences the redox status and NPQ of Karenia brevis by way of thioredoxin reductase. Harmful Algae, 71, 29-39
Colon, R., & Rein, K. S. (2021). Essential components of the xanthophyll cycle differ in high and low toxin Karenia brevis. Harmful Algae, 103, 102006.
Colon, Ricardo, "High and Low Toxin Producing Strains of Karenia Brevis Differ Significantly in the Redox Proteome, Lipid Profiles, and Xanthophyll Cycle Pigments" (2021). FIU Electronic Theses and Dissertations. 4746.
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