Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Chemistry

First Advisor's Name

John P. Berry

First Advisor's Committee Title

Committee Chair

Second Advisor's Name

Ligia Collado-Vides

Second Advisor's Committee Title

Committee Member

Third Advisor's Name

Anthony P. DeCaprio

Third Advisor's Committee Title

Committee Member

Fourth Advisor's Name

Piero R. Gardinali

Fourth Advisor's Committee Title

Committee Member

Fifth Advisor's Name

Johanna Mejia-Fava

Fifth Advisor's Committee Title

Committee Member

Sixth Advisor's Name

Yuk-Ching Tse-Dinh

Sixth Advisor's Committee Title

Committee Member

Keywords

Lyngbya, Neolyngbya, cyanobacteria, Harmful Algal Bloom, Brevetoxin, Eudesmacarbonate, Tursiops truncatus, Bottlenose Dolphins, Intoxication, Florida Keys, Danio rerio, Zebrafish, Neurotoxicity

Date of Defense

4-1-2020

Abstract

Bottlenose dolphins (Tursiops truncatus) living in captivity in the Florida Keys have recently been observed grazing macrophytic algal communities, and particularly, filamentous cyanobacteria, within their enclosures, and subsequently presenting apparent signs of intoxication. Collections of a mixed assemblage of marine filamentous cyanobacteria were morphologically related to the taxonomically complex and toxigenic polyphyletic genus, Lyngbya, sensu lato. Phylogenetic characterization, using 16S rDNA methods, identified an undescribed member of the recently accepted genus Neolyngbya (Oscillatoriales) among Neolyngbya arenicola, and an unknown Oscillatoriacean species within a poorly resolved clade clustering between the genera Limnoraphis and Capilliphycus.

A dual approach was subsequently utilized to identify a putative neurotoxic metabolite from cyanobacteria associated with the intoxication events. Initial chemical screening was unable to detect recognized algal and cyanobacterial neurotoxins including anatoxin-a, brevetoxin-2 (PbTx-2), domoic acid, b-methylamino-L-alanine and saxitoxin. In tandem, however, toxicity testing – and concomitant bioassay-guided fractionation- based on early life stages (i.e., embryo, larvae) of the zebrafish (Danio rerio) as a vertebrate toxicological model, was employed to identify relevant metabolites from cyanobacterial collections. Using the latter approach, relevant toxicity including, particularly, endpoints of neurotoxicity were identified for extracts and subsequent fractions. Apparent neurotoxicity was comparatively assessed against the recognized algal neurotoxin, PbTx-2. Crude lipophilic extracts, and subsequent chemical fractions, notably aligned with observed neurotoxic effects of PbTx-2. Further bioassay-guided fractionation enabled purification and structural elucidation of a previously undocumented, neurotoxic metabolite, (4S,5R,6R,7S,10S)-eudesman-(4S,6R)-cyclocarbonate (i.e., eudesmacarbonate), from the mixed filamentous cyanobacteria (dominated by Neolyngbya sp.) which, may, in turn, contribute to the observed intoxications of captive dolphins.

Identifier

FIDC008959

Available for download on Thursday, March 10, 2022

Included in

Chemistry Commons

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