Plants, bats magnify neurotoxin in Guam

Researchers have turned up new evidence that a natural toxin that grows more concentrated as it moves up the food chain might have caused a puzzling spike in a neurodegenerative disease in Guam.

BOTTOM LINK. Neurotoxin in a cycad derives from bacteria (green) living in specialized roots. Cox

Starting in the mid-20th century, this disease–which shares traits with Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis (ALS), also known as Lou Gehrig’s disease–began increasing among Guam’s Chamorro people (SN: 5/17/03, p. 310: Available to subscribers at Troubling Treat: Guam mystery disease from bat entrée?). Last year, scientists proposed a new explanation: The presence of flying foxes, a type of bat, on the dinner plate rose with the availability of guns and then declined as the bats became extinct. Abundance of the delicacy exposed people to more of the

neurotoxin beta-methylamino-L-alanine (BMAA) that comes from a local plant that these bats eat, researchers hypothesized.

Concentrations of the neurotoxin indeed rise along the food chain, report ethnobotanist Paul Alan Cox of the National Tropical Botanical Garden based in Kalaheo, Hawaii, and his colleagues in the Nov. 11 Proceedings of the National Academy of Sciences. The bottom link of the chain was a surprise, though. Botanists had assumed that cycad plants, which look like palm trees, produce BMAA. But Cox and his coworkers Susan Murch and Sandra Banack found that the BMAA in these plants derives from nitrogen-fixing cyanobacteria that live in certain roots.

The cycads transport BMAA to tissues around their seeds, the researchers say. Murch also found the neurotoxin in brain tissue from disease victims in Chamorro. Intriguingly, the researchers also detected BMAA in brain tissue from two Canadians who died of Alzheimer’s disease.

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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.

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