What causes magic mushrooms to develop a blue hue when sliced or bruised?
Well, this long-standing puzzle has recently been deciphered by chemists, leading to the surprising discovery that the deep blue pigments involved are akin to indigo, the colorant used in making blue jeans.
Magic mushrooms, also known as Psilocybe, are a type of fungus that generates the psychoactive compounds psilocybin and psilocin. Among various species, they’re known for their immediate shift to a blue tone upon being cut or injured. In Boletales mushrooms, this color transition is due to the oxidation of gyrocyanin or pulvinic acid. However, this explanation doesn’t hold for Psilocybe mushrooms.
Prior studies suggested the bluish transformation was triggered by the oxidation of psilocybin. Yet, the true identity of the pigment and the biochemical processes that led to its formation remained uncertain.
Over the years, Dirk Hoffmeister and his team at the Leibniz Institute for Natural Product Research and Infection Biology in Germany have been conducting research on Psilocybe cubensis. They had observed the intriguing shift to blue multiple times in their lab-grown mushrooms. As Hoffmeister explains, their drive stemmed from pure curiosity to decipher a phenomenon that has been recognized for many years.
Despite numerous attempts, the team was unsuccessful in their efforts to isolate and purify this elusive blue compound. This challenge, rather than dissuading them, served as a compelling incentive. They wanted to go one step further than all other previous researchers had managed to go and decided to do so using unconventional analytical methods.
The research team explored a range of advanced analytical methods, such as liquid chromatography-mass spectrometry, Maldi mass spectrometry, infrared spectroscopy, and time-resolved nuclear magnetic resonance spectroscopy to monitor the formation of the compounds.
The pigment wasn’t a singular substance but rather a complex amalgamation of interlinked psilocybin oxidation products. Among them, most were quinoid psilocyl oligomers – substances bearing a striking resemblance to indigo, the vivid blue dye utilized in jeans. According to Claudius Lenz, the study’s lead author, both the blue compounds and indigo share structural similarities in their indole core, and the color origin in both cases is a quinoid.
The team isolated six mushroom pigments, all of which are outcomes of a cascade reaction initiated with psilocybin. This reaction involves the phosphatase enzyme stripping off its phosphate group to transform into psilocin. Following this, an oxidizing laccase forms psilocyl radicals that bind to create C-5 coupled subunits, which further polymerize via C-7. “Their elucidation of the cascade reaction is quite remarkable,” comments Jaclyn Winter, a researcher specializing in the biosynthesis of natural products in bacteria and fungi at the University of Utah, US.
The precise function of these blue pigments, however, is still unclear. “We theorize, without any supportive evidence yet, that these pigments could potentially play a defensive role, possibly acting as a deterrent against predators,” suggests Hoffmeister. These compounds may generate reactive oxygen species, toxic to insects nibbling on the mushrooms. Winter predicts considerable forthcoming research dedicated to unraveling the actual ecological role of these molecules.
Hoffmeister’s aspiration extends beyond inspiring further fungal studies from a chemical standpoint. He also hopes to alter the prevailing perceptions about psilocybin. He articulates, “Psilocybin is often associated with illicit recreational use, yet it holds promising potential as a treatment for therapy-resistant depression.”
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