seafood dish

Paralytic shellfish poisoning is caused by eating contaminated shellfish © Frits Hoogesteger

Scientists in Malaysia have identified a gene coding for the production of a harmful toxin in the marine dinoflagellate Alexandrium minutum.

The toxin in question is responsible for ‘paralytic shellfish poisoning’ which causes toxicity and mortality for those eating contaminated shellfish.

Understanding how the toxins are produced could help scientists to develop preventative strategies.

Paralytic shellfish poisoning (also known as PSP) is widely reported in Southeast Asia, and is caused by eating shellfish contaminated with a biotoxin called saxitoxin.

Saxitoxin accumulates in filter-feeding shellfish including mussels, clams and oysters when they ingest microscopic saxitoxin-producing algae such as cyanobacteria or dinoflagellates. In humans this toxin blocks sodium channels in the nerves, causing paralysis and death. There is no known antidote.

Current efforts aim to identify the genes which code for saxitoxin production, but is difficult to do, given that saxitoxin is produced as the result of many interconnected molecular pathways which all involve different enzymes and proteins. In addition, it is likely to be synthesised differently in different organisms.

Greatly enlarged (1000x) model of a tiny dinoflagellate

Greatly enlarged (1000x) model of a tiny dinoflagellate on display at the Sant Ocean Hall in the National Museum of Natural History in Washington, DC. © Mr T in DC

In Malaysia the main culprits are three dinoflagellates: Alexandrium minutum, A. tamiyavanichii and Pyrodinium bahamense compressum. Until recently, the saxitoxin genes and biosynthesis pathways in all three of these species remained a mystery, but researchers from Universiti Malaysia Sarawak have now identified a saxitoxin biosynthesis gene in A. minutum using a ‘reverse genetics’ approach, whereby gene sequences are used to investigate unknown traits or characteristics.

They found the gene which codes for an enzyme called OTC, which is responsible for one of the crucial first steps in saxitoxin production.

The team hopes to characterise more genes involved in saxitoxin synthesis using similar techniques. In future, it may be possible to genetically manipulate dinoflagellate algae by blocking the action of crucial enzymes so that it cannot manufacture the poison and therefore can’t contaminate shellfish or water supplies.

Finding the right target genes is crucial, however, as knocking out the wrong enzymes could disrupt other cell processes and limit the algae’s survival.

For further information contact:

Dr Leaw Chui Pin
Institute of Biodiversity and Environmental Conservation
Universiti Malaysia Sarawak