Page 305 - Algae

288 Algae: Anatomy, Biochemistry, and Biotechnology

mussels (Mytilus edulis). Scallops are reported not to contain these elimination bacteria. Ancho-
vies can also contain domoic acid in their guts, by feeding on toxic Pseudonitzschia spp.; this
toxin affects their behavior and survival. Effects are also seen in seals. In humans, consumption
of contaminated seafood mostly affected the elderly or infirm. Heat does not destroy domoic
acid, although shellfish toxicity can decrease during cooking or freezing via domoic acid transfer
from the meats to the surrounding liquid. The sea otter is the only animal known to be able to
avoid intoxication, probably recognizing toxic prey by their odor. The mechanism of domoic acid
toxicity is explained by its structural similarity with the excitatory neurotransmitter glutamic acid
and its analogs, but with a much stronger receptor affinity. Domoic acid is three times more
potent than its analog kainic acid and up to 100 times more potent than glutamic acid. After
exposure, domoic acid binds predominately to N-methyl-D-aspartate (NMDA) receptors in the
central nervous system, causing depolarization of the neurones. Subsequently, the intercellular
calcium concentration increases, resulting in sustained activation of calcium-sensitive enzymes,
eventually leading to depletion of energy, neuronal swelling, and cell death. The affected
neurones are mainly located in the hippocampus, explaining the most striking effect of
domoic acid poisoning, which is short-term memory loss, observed in 25% of the affected
persons in the 1987 contaminated mussel event. Other symptoms are confusion, nausea,
vomiting, gastroenteritis, cramps and diarrhea, all within 24 h. Neurological complaints, includ-
ing ataxia, headaches, disorientation, difficulty in breathing and coma, develop 48 h after
consumption. Permanent brain damage can also be caused by domoic acid intoxication.
Effects of chronic low level ingestion are unknown. Domoic acid from mussels is more neuro-
toxic than the chemically pure compound. This increase is due to domoic acid potentiation,
caused by high concentrations of glutamic and aspartic acids present in mussel tissue. This
neurotoxic synergism occurs through a reduction in the voltage-dependent Mg 2 block at the
receptor associated channel, following activation of non-NMDA receptors, in addition to the
NMDA receptor activation by domoic acid itself.
Intensive research over the last years has revealed a new class of phytotoxins produced by
diatoms with more subtle and less specific effects, a discovery that has drawn a lot of attention
as the diatoms have traditionally been regarded a key component of the food chain. Three

TABLE 7.8
Summary of Toxic Algae and the Corresponding Metabolites
Scientific Name Class Toxin

Nodularia spp. Cyanophyceae Nodularin
Microcystis spp. Cyanophyceae Microcystin
Chondrus armata Floridophyceae ASP domoic acid
Prymnesium parvum Haptophyceae Fish toxin
Phaeocystis pouchetii Haptophyceae PUA
Chrysochromulina polylepis Haptophyceae Ichtytoxic glycolipids
Alexandrium spp. Dinophyceae PSP
Dinophysis spp. Dinophyceae DSP
Prorocentrum lima Dinophyceae DSP
Gymnodinium breve Dinophyceae NSP
Ptychodiscus brevis Dinophyceae NSP
Gambierdiscus toxicus Dinophyceae Ciguatoxin/maitotoxin
Pseudonizschia spp. Bacillariophyceae ASP domoic acid
Thalassiosira rotula Bacillariophyceae PUA
Skeletonema costatum Bacillariophyceae PUA