A critical discovery about harmful algal toxins.

A new study published in Nature magazine reveals the molecular basis for resistance and accumulation of paralytic shellfish toxins (PSTs) in softshell clams. Titled A Molecular Basis for Differential Susceptibility and Accumulation of Paralytic Shellfish Poisoning Toxins in Commercial Bivalves, the study was supported by grants from NOAA's Ecology and Oceanography of Harmful Algal Blooms (ECOHAB) program and the National Institutes of Health (NIH).

Paralytic shellfish poisoning is a persistent problem along the East and West coasts of the United States and is caused by algae that naturally produce PSTs. Shellfish feed on these toxic algae and can accumulate concentrations of toxins unsafe for human consumption.

"Harmful algal blooms pose a serious threat to human health and are economically challenging to our coastal communities," said retired Navy Vice Admiral Conrad C. Lautenbacher, Jr., Ph.D., undersecretary of commerce for oceans and atmosphere and NOAA administrator.

Saxitoxin and other PSTs are potent neurotoxins that block movement of sodium through sodium channels in nerve cell membranes, halting the flow of nerve impulses and thereby causing paralysis. Humans who consume affected shellfish can suffer from the paralytic effects of these toxins. There is currently no antidote for paralytic shellfish poisoning, and all cases require immediate medical attention.

The research project began in the late 1990s with the finding that softshell clams from an area that is frequently affected by harmful algal blooms are more resistant to the toxic effects of PSTs than softshell clams from areas that have not experienced harmful algal blooms.

In subsequent research, the scientists discovered that the resistance to PSTs is caused by a mutation in the gene for sodium channels, which makes them more than 1,000 times less sensitive to saxitoxin. This toxin resistance allows the clams to survive and feed during harmful algal blooms and thereby accumulate the high levels of PSTs that cause paralytic shellfish poisoning in humans.

"With this information we may be able to eventually develop genetic markers and selectively breed shellfish stocks that accumulate little or no PST in a given region, reducing paralytic shellfish poisoning incidents and harvest losses, as well as be able to predict the evolution of resistance in areas that have only recently experienced paralytic-shellfish-poisoning outbreaks," commented Monica Bricelj, lead author of the study.