The hallucinogenic effects of magic mushrooms are well documented. But nobody knows what psilocybin, the chemical responsible, does for the mushrooms themselves.
Now, one of the first genomic analyses of hallucinogenic fungi has deciphered psilocybin production, and even suggested a function for it. By messing with insect neurochemistry, psilocybin may act as a psychedelic repellent.
A team of researchers led by Jason Slot at Ohio State University compared the genomes of three hallucinogenic fungi with three non-hallucinogenic relatives. By doing so, they identified the cluster of genes responsible for making psilocybin (bioRxiv, doi.org/cbx2).
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The gene cluster is found in several distantly related groups, suggesting that the fungi swapped genes in a process called horizontal gene transfer. This is uncommon in mushrooms: it is the first time genes for a compound that is not necessary for the fungi’s survival – called a secondary metabolite – have been found moving between mushroom lineages.
Since these genes have survived in multiple species, Slot thinks psilocybin must be useful to the fungi. “Strong selection could be the reason this gene cluster was able to overcome the barriers to horizontal gene transfer,” he says.
Hallucinogenic mushrooms often inhabit areas rich in fungi-eating insects, so Slot suggests psilocybin might protect the fungi, or repel insects from a shared food source, by somehow influencing their behaviour.
The specific purpose of many secondary metabolites is unknown, says Peter Spiteller at the University of Bremen, Germany. But that’s not to say they don’t have a use. “Secondary metabolites are not just produced for fun,” he says.
However, while psilocybin has been shown to affect the brains of mammals including mice, there is little evidence that it affects insects or other invertebrates – barring a famous 1962 study showing that it changes the way spiders build webs.
That said, other fungi use similar substances to influence insects, “for example the zombie ant fungus,” says Slot. And insects have nervous system receptors similar to those affected by the psilocybin successor molecule psilocin in humans.
In a second study, a group led by Dirk Hoffmeister at Friedrich Schiller University Jena in Germany was able to go one step further. After obtaining a legal permit, they have developed a way to make psilocybin using enzymes (Angewandte Chemie, doi.org/gbp6hh).
This has never been done before and could set the stage for commercial production. In recent years there has been a revival of interest in psilocybin’s potential as a therapeutic drug, an area of research that had stalled due to tough 1970s drug laws.