Light microscope and transmission electron microscope photographs of Pseudo-nitzschia pungens var. Pungens (top two photos) and Pseudo-nitzschia brasiliana (bottom two photos) found in Luzon shellfish farms. Both species produce domoic acid, a dangerous neurotoxin. Credit: Botavara et al.

The densely-populated island of Luzon is home to over half of the Philippines’ population, many of whom consume shellfish on a regular basis. An international team of scientists has just confirmed the presence there of two species of Pseudo-nitzschia diatoms capable of producing a dangerous neurotoxin that can cause severe sickness and memory loss.

The research is published in the journal Diatom Research.
Poetically described as “algae that live in glass houses,” diatoms are microscopic aquatic organisms that cover themselves in protective milk-colored silica shells. While most diatom species are harmless, half of the 58 known species from the genus Pseudo-nitzschia are notorious for producing domoic acid (DA).
A person who has eaten DA-infected shellfish may experience vomiting, nausea, diarrhea, and abdominal cramps. In some cases, DA has even caused the permanent loss of short-term memory in a condition known as “amnesic shellfish poisoning” (ASP).
Despite this danger, little is known about the extent of Pseudo-nitzschia proliferation in the Philippines. This prompted scientists from the Ateneo de Manila University Department of Biology and from Universiti Malaysia Sarawak to study the physical and genetic characteristics of the diatoms in water samples from shellfish farms in Bacoor Bay and Pagbilao Bay in Luzon.
“It is important to be aware of the toxic potential of these diatoms and to monitor them accordingly, but such efforts must begin by establishing their presence in our waters. To our knowledge, the molecular taxonomy of Pseudo-nitzschia in the Philippines is virtually nonexistent,” say researchers Lorenzo A. Botavara, Janice A. Ragaza, Hong Chang Lim, and Sing Tung Teng.
They confirmed the presence of the DA-producing diatoms Pseudo-nitzschia pungens and Pseudo-nitzschia brasiliana in the samples. They also noted that this is the first time that P. brasiliana has ever been found in Luzon.
At times of excessive growth called harmful algal blooms (HABs) or “red tide,” DA can accumulate in large amounts in filter-feeding shellfish such as mussels and clams.
Thus, “confirming species identities of a genus with half of its constituents known to produce DA is essential to HAB monitoring (in the Philippines),” the scientists say.

More information:
Lorenzo A. Botavara et al, Morphological and molecular characterization of two potentially toxigenic species of the genus Pseudo-nitzschia (Bacillariophyceae) in Luzon Island, Philippines, Diatom Research (2024). DOI: 10.1080/0269249X.2024.2401968

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Ateneo de Manila University

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Amnesia-causing diatoms found in Luzon shellfish farms (2024, November 7)
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