[“Fungal appetites are diverse, but there are some materials they won’t break down unless they have to. In one of his workshops, McCoy explained how he had trained Pleurotus mycelium to digest one of the most commonly littered items in the world, cigarette butts, more than 750 thousand tons of which are thrown away every year. Unused cigarette butts will break down, given time, but used cigarette butts are saturated with toxic residues that impede the process. McCoy had weaned Pleurotus onto a diet of used butts by gradually phasing out the alternatives. Over time, the fungus had “learned” how to use them as its sole food source. A time-lapse video showed the mycelium seeping steadily upward through a jam jar filled with crumpled tar-stained butts. A burly oyster mushroom soon bundled itself up and out of the top.
In fact, it is just as much “remembering” as “learning.” A fungus won’t produce an enzyme it doesn’t need. Enzymes, or even entire metabolic pathways, can lie dormant in fungal genomes for generations. For the Pleurotus mycelium to digest the used cigarette butts it might have to dust off an unused metabolic move. Or it might deploy an enzyme normally used for something else and press it into the service of a new cause. Many fungal enzymes, like lignin peroxidases, are not specific. This means that a single enzyme can serve as a multitool, allowing the fungus to metabolize different compounds with similar structures.
As it happens, many toxic pollutants—including those in cigarette butts—resemble the by-products of lignin breakdown. In this sense, to confront Pleurotus mycelium with used cigarette butts is to offer it a commonplace challenge. Much of radical mycology is underwritten by the radical chemistry of white rot fungi. However, it isn’t always easy to predict what a given fungal strain will metabolize. McCoy told us about his attempts to grow Pleurotus mycelium on dishes spotted with drops of the herbicide glyphosate. Some of the Pleurotus strains avoided the drops. Some grew straight through them. Some grew up to the edge of a drop and stopped growing. “It took those ones a week to work out how to break it down,” McCoy recalled. He likened fungi to jailers with bunches of enzymatic keys that can unlock certain chemical bonds. Some strains might have the right key ready to go. Others might have it buried somewhere inside their genome but choose to avoid the new substance anyway. Others might take a week to riffle through the bunch of keys, trying different ones until they get lucky.”]
Merlin Sheldrake, Entangled Life
