Don’t Eat Fruit Bats, and Avoid Algae Blooms!

The peo­ple with the world’s high­est risk of Lou Gehrig’s dis­ease were the Chamor­ro peo­ple, who were the native peo­ple of Guam. These peo­ple also had a high risk of Alzheimer-like demen­tia and dis­or­ders like parkin­son­ism. The prob­lem didn’t seem to be genet­ic or con­ta­gious, and the dis­eases became less com­mon when the pop­u­la­tion became more Amer­i­can­ized after World War II. These facts sug­gest­ed that the prob­lem result­ed from some­thing that the peo­ple had been eat­ing.

The prime sus­pect in this case is a neu­ro­tox­in called BMAA (beta-methy­lamino-L-ala­nine). It’s sim­i­lar to the amino acid ala­nine that your body uses in mak­ing pro­tein. When BMAA was giv­en to rhe­sus macaques, the result­ing dam­age to the ner­vous sys­tem was sim­i­lar to what was hap­pen­ing to the afflict­ed peo­ple on Guam.

The BMAA orig­i­nal­ly came from cyanobac­te­ria. The cyanobac­te­ria are true bac­te­ria, although they are some­times called blue-green algae. The cycad plant, which was an impor­tant food source for the Chamor­ro peo­ple, has a part­ner­ship (sym­bi­ot­ic rela­tion­ship) with cyanobac­te­ria of the genus Nos­toc. The cycads give some sug­ar to the Nos­toc liv­ing on their roots. In return, the Nos­toc con­vert some of the nitro­gen from the atmos­phere into ammo­nia, which the cycad can use as fer­til­iz­er.

Unfor­tu­nate­ly, the Nos­toc also make some BMAA, which is also absorbed by the cycad. The Chamor­ro peo­ple then were exposed to BMAA when they ate seeds from the cycad plant. They got an even big­ger dose of BMAA when they ate fruit bats, because the BMAA had become con­cen­trat­ed in the bats’ bod­ies. This process of con­cen­tra­tion is called bioac­cu­mu­la­tion.

There are two take-home lessons from this sto­ry. The first is that we may need to be care­ful about human expo­sure to cyanobac­te­ria. All types of cyanobac­te­ria but only cyanobac­te­ria pro­duce BMAA. Human beings could be exposed to BMAA as a result of the tox­ic algae blooms that are becom­ing increas­ing­ly com­mon because of fer­til­iz­er runoff. Peo­ple could become exposed to BMAA by drink­ing or swim­ming in con­t­a­m­i­nat­ed water, such as the water in ponds and reser­voirs. They could also be exposed to BMAA through cyanobac­te­ria in foods or sup­ple­ments made from algae.

The sec­ond les­son is that BMAA, like many oth­er tox­ins, becomes more con­cen­trat­ed as you move up the food chain. Fruit bats con­tained more BMAA than the cycad seeds did. Oth­er tox­ins, such as diox­in and mer­cury, also con­cen­trate as you go up the food chain. It’s anoth­er rea­son why it’s bet­ter for us to eat plants, not ani­mals.

Pho­to by Tam­bako the Jaguar