Neurotoxin-producing diatoms

Amyotrophic lateral sclerosis, or ALS, commonly known as ‘Lou Gehrig’s disease,’ a neurodegenerative disease that destroys motor neurons and eventually leads to paralysis and death, currently affects about 30,000 people in the United States. (Before she passed away in 2009, my grandmother numbered among them.)

In recent years, scientists have discovered a link between ALS (and other neurodegenerative diseases) and a neurotoxin produced by cyanobacteria called β-N-methylamino-L-alanine, or BMAA. Cyanobacteria, along with other types of algae, form the base of the aquatic food web; as algae is consumed by zooplankton, and zooplankton are eaten by larger organisms in turn, the neurotoxin can accumulate in animals that may end up on the menu for humans, including oysters, mussels, crabs, and other seafood.

Earlier this year, a team of scientists reported the discovery of an additional source of BMAA in aquatic environments in the journal PLoS ONE. Diatoms, intricate single-celled photosynthetic organisms that are nearly ubiquitous in aquatic environments, and which are eaten by a variety of larger organisms – much like cyanobacteria – also produce BMAA.

The researchers found BMAA in each of the six species of diatoms they cultured in the lab. From samples of naturally occurring diatoms collected off the west coast of Sweden, they identified four dominant groups of diatoms, one of which contained BMAA.

The natural samples contained both diatoms and cyanobacteria. An experimental inhibition of diatom growth in the BMAA-producing samples (elicited by adding a compound which deters diatom growth but doesn’t affect cyanobacteria) resulted in BMAA levels that were one-third the amount detected in untreated samples, suggesting that two-thirds of the BMAA was produced by diatoms.

The production of BMAA by an additional group of aquatic organisms is cause for concern, according to the scientists. “Taken together, the data reported here give a clear answer supported by solid evidence that BMAA is not exclusively produced by cyanobacteria. As diatoms are a major bloom-forming phytoplankton in aquatic environments, the impact of this discovery suggests new bioaccumulation routes and that the risk of human exposure may have increased tremendously.”

Several species of diatoms magnified under a microscope. Rigid cell walls made of silica result in the intricate, crystalline structures characteristic of diatoms. 

(Original image by Wipeter via Wikimedia Commons)