Cyanobacteria produce high levels of ergothioneine

Ergothioneine (ET) is a unique natural antioxidant. We have examined the origin of ET in zebrafish. There was virtually no ET, measured by LC–MS, in most tank vegetation (plant, green and red alga). However, ET was detected in a Phormidium sample, a cyanobacterium. In commercial fish feed preparations, ET content increased with the content of cyanobacteria Arthrospira platensis or Arthrospira maxima (Spirulina). High levels of ET (up to 0.8 mg per g dry mass) were measured in cyanobacteria preparations sold as dietary supplements for humans and in fresh Scytonema and Oscillatoria cultures. Cyanobacteria contained as much ET as King Oyster mushrooms (Pleurotus eryngii). All samples with substantial ET content also contained the biosynthesis intermediate hercynine; this strongly suggests that cyanobacteria synthesise ET de novo. In conclusion, our data establish that cyanobacteria can produce high levels of ergothioneine. Spirulina is a novel, safe, accessible, and affordable source of ergothioneine for humans.