Domoic acid (DA) is a naturally occurring cyanotoxin, which upon ingestion, is responsible for amnesic shellfish poisoning (ASP) in both humans and animals. Produced by the marine diatom, Pseudonitzschia, DA is accumulated by a number of marine organisms including shellfish, clams and mussels which upon consumption can lead to headaches, nausea and seizures. Possessing a variety of functional groups the structure of DA contains three carboxyl groups, a pyrrole ring and a potent conjugated diene region allowing for binding to glutamate receptors in the dorsal hippocampus of the brain causing the described detrimental effects. Although limitations have been placed regarding the amount of DA that may be contained in seafood no limitations have been placed on the amount present in drinking water. Natural degradation of the toxin may occur through reactive oxygen species such as the hydroxyl radical and singlet oxygen at the conjugated diene region. In this work the photooxidation of DA via singlet oxygen has been studied using sorbic acid as a model compound. The three major reaction pathways observed during the photooxdiation process for both acids include 2 + 4 cycloaddition to produce endoperoxides , 2 + 2 reaction to afford aldehydes and ketones or an ene reaction to generate hydroperoxides. Under similar reaction conditions for SA and DA, the endoperoxide has been seen to be the major product for photoxidation of SA while the hydroperoxide has been seen to be the dominant product during photooxidation of DA.

Diatoms play a fundamental role in marine food webs, and significantly contribute to global primary production and carbon sequestration into the deep ocean. In many offshore areas of the open ocean, iron (Fe) input is low, and its availability often limits phytoplankton biomass. Recently, gene sequences encoding ferritin, a nearly ubiquitous iron storage and detoxifying protein, have been identified in pennate diatoms such as Pseudo-nitzschia, but not in other Stramenopiles (which include centric diatoms, brown algae and some protist plant parasites) or Cryptophyte relatives. Members of this genus readily bloom upon addition of iron to Fe-limited waters, and are known to produce the neurotoxin domoic acid. Until now, the reason for the success of pennate diatoms in the open ocean was uncertain; however, expressing ferritin would allow pennate species to store Fe after a transient input, using it to dominate Fe stimulated algal blooms. Here, the ferritin gene was cloned from the coastal pennate diatom Pseudonitzschia multiseries, overexpressed in Escherichia coli, and purified using liquid chromatography. The ferritin protein sequence appears to encode a non-heme, ferritinlike di-iron carboxylate protein, while gel filtration chromatography and SDS-PAGE indicate that this ferritin is part of the 24 subunit maxi-ferritins. Spectroscopically monitoring the addition of Fe(II) to a buffered ferritin solution shows that the P. multiseries protein demonstrates ferroxidase activity, binding iron and storing it as Fe(III) in excess of 600 equivalents per protein shell. In keeping with the typical stoichiometry of the ferroxidase reaction, oxygen (O₂) is consumed in a 2 Fe:O₂ratio while hydrogen peroxide is produced concurrently. iii Diatoms evolved from secondary endosymbiosis involving eukaryotic red algae; however, a broad phylogenetic comparison suggests that P. multiseries ferritin was likely acquired via lateral gene transfer from cyanobacteria – not from its ancestral endosymbionts. Until recently, no other ferritins have been identified in diatoms, and the protein characterized here is unique in that it seems to be derived from a prokaryotic organism yet it occurs in a marine eukaryote. These findings have direct implications for the success of pennate diatoms in both Fe rich coastal waters and upon Fe addition in the open ocean.

Diatoms play a fundamental role in marine food webs, and significantly contribute to global primary production and carbon sequestration into the deep ocean. In many offshore areas of the open ocean, iron (Fe) input is low, and its availability often limits phytoplankton biomass. Recently, gene sequences encoding ferritin, a nearly ubiquitous iron storage and detoxifying protein, have been identified in pennate diatoms such as Pseudo-nitzschia, but not in other Stramenopiles (which include centric diatoms, brown algae and some protist plant parasites) or Cryptophyte relatives. Members of this genus readily bloom upon addition of iron to Fe-limited waters, and are known to produce the neurotoxin domoic acid. Until now, the reason for the success of pennate diatoms in the open ocean was uncertain; however, expressing ferritin would allow pennate species to store Fe after a transient input, using it to dominate Fe stimulated algal blooms. Here, the ferritin gene was cloned from the coastal pennate diatom Pseudonitzschia multiseries, overexpressed in Escherichia coli, and purified using liquid chromatography. The ferritin protein sequence appears to encode a non-heme, ferritinlike di-iron carboxylate protein, while gel filtration chromatography and SDS-PAGE indicate that this ferritin is part of the 24 subunit maxi-ferritins. Spectroscopically monitoring the addition of Fe(II) to a buffered ferritin solution shows that the P. multiseries protein demonstrates ferroxidase activity, binding iron and storing it as Fe(III) in excess of 600 equivalents per protein shell. In keeping with the typical stoichiometry of the ferroxidase reaction, oxygen (O₂) is consumed in a 2 Fe:O₂ratio while hydrogen peroxide is produced concurrently. iii Diatoms evolved from secondary endosymbiosis involving eukaryotic red algae; however, a broad phylogenetic comparison suggests that P. multiseries ferritin was likely acquired via lateral gene transfer from cyanobacteria – not from its ancestral endosymbionts. Until recently, no other ferritins have been identified in diatoms, and the protein characterized here is unique in that it seems to be derived from a prokaryotic organism yet it occurs in a marine eukaryote. These findings have direct implications for the success of pennate diatoms in both Fe rich coastal waters and upon Fe addition in the open ocean.

Diatoms play a fundamental role in marine food webs, and significantly contribute to global primary production and carbon sequestration into the deep ocean. In many offshore areas of the open ocean, iron (Fe) input is low, and its availability often limits phytoplankton biomass. Recently, gene sequences encoding ferritin, a nearly ubiquitous iron storage and detoxifying protein, have been identified in pennate diatoms such as Pseudo-nitzschia, but not in other Stramenopiles (which include centric diatoms, brown algae and some protist plant parasites) or Cryptophyte relatives. Members of this genus readily bloom upon addition of iron to Fe-limited waters, and are known to produce the neurotoxin domoic acid. Until now, the reason for the success of pennate diatoms in the open ocean was uncertain; however, expressing ferritin would allow pennate species to store Fe after a transient input, using it to dominate Fe stimulated algal blooms. Here, the ferritin gene was cloned from the coastal pennate diatom Pseudonitzschia multiseries, overexpressed in Escherichia coli, and purified using liquid chromatography. The ferritin protein sequence appears to encode a non-heme, ferritinlike di-iron carboxylate protein, while gel filtration chromatography and SDS-PAGE indicate that this ferritin is part of the 24 subunit maxi-ferritins. Spectroscopically monitoring the addition of Fe(II) to a buffered ferritin solution shows that the P. multiseries protein demonstrates ferroxidase activity, binding iron and storing it as Fe(III) in excess of 600 equivalents per protein shell. In keeping with the typical stoichiometry of the ferroxidase reaction, oxygen (O₂) is consumed in a 2 Fe:O₂ratio while hydrogen peroxide is produced concurrently. iii Diatoms evolved from secondary endosymbiosis involving eukaryotic red algae; however, a broad phylogenetic comparison suggests that P. multiseries ferritin was likely acquired via lateral gene transfer from cyanobacteria – not from its ancestral endosymbionts. Until recently, no other ferritins have been identified in diatoms, and the protein characterized here is unique in that it seems to be derived from a prokaryotic organism yet it occurs in a marine eukaryote. These findings have direct implications for the success of pennate diatoms in both Fe rich coastal waters and upon Fe addition in the open ocean. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate