Many cyanobacteria make a neurotoxin

A brain-damaging toxin, once believed to come only from a group of tropical plants and their live-in microbes, turns out to be much more widespread.

The discovery comes out of investigations into a long-standing medical mystery. During the last century, a neurological disease akin to amyotrophic lateral sclerosis spiked among the Chamorro people in Guam. An international research team led by Paul Cox of the National Tropical Botanical Garden based in Kalaheo, Hawaii, has suggested that the spike came from a rise in exposure to the neurotoxic amino acid β-N-methylamino-L alanine (BMAA).

According to this theory, the toxin becomes more concentrated as it moves up the food chain from the microbes, Nostoc cyanobacteria, to tropical plants called cycads to bats to the Chamorro people (SN: 8/14/04, p. 110: Available to subscribers at Mechanism suggested for Guam illness).

Now, Cox’s team suggests that people far from Guam could be exposed to BMAA. A survey found the toxin in 20 of 21 genera of cyanobacteria that live in water and soil around the world, the researchers report in the April 5 Proceedings of the National Academy of Sciences. They also isolated the toxin from cyanobacteria living symbiotically with other organisms, including a lichen and four species of flowering plants.

In other small, preliminary studies, the researchers also found BMAA in brain tissues of 9 Canadians who died with Alzheimer’s disease, but not in the brains of 14 others who died of causes not related to neurological disease. However, the researchers caution that the link between BMAA and neurological diseases remains unclear.

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.