Periodically I see articles like about “plastic-eating mushrooms”: https://www.smithsonianmag.com/smart-news/chow-down-plastic-eating-fungus-180958127/
Here’s my take, copied from the Fungal Materials facebook group:
There are fungi that can eat one kind of plastic - polyurethane. The biochemical explanation is that plastic is made of chained hydrocarbons, and fungi eat hydrocarbons. They are just very difficult to digest.
The plastic must be degraded first, and mixed with a nutritional medium, and sterilized or pasteurized, and then the fungi grow slowly. This is expensive and there’s no way we will do that instead of chucking plastics into landfills.
This project is a bit unintentionally misleading, I think. Unless I’m missing some things.
The species that can eat polyurethane (a subset of plastics) is Pestalotiopsis microspora. This species in its natural habitat is endopyhtic, meaning it lives as a symbiote inside plants. It is a fungus, but it does not make mushrooms, edible or otherwise.
In this project however, they use Pleurotus and Schizophyllum species, which nowhere else have I ever heard of being able to digest any kind of plastic. I’m pretty sure they did some research, found that those species are good for bioremediation (which they are) and then made a leap to them digesting plastic. [ As was pointed out by a member of the Fungal Materials facebook group, Pleurotus spp, Schizophyllum spp and maybe others can consume photo-degraded polyethylene. So I was partially off-base there! ]
So, as far as I know, there are no mushrooms that grow on plastic. And there is no even remotely feasible mechanism for remediating plastics with fungi, even though technically it is possible.
In terms of dealing with plastic waste, the greatest potential for fungi is to reduce the original use of plastics by developing biofab techniques to replace them.
The question also came up about if CRISPR could be used to engineer a fungus that would consume plastic more quickly. I don’t know enough about the chemistry to say for sure, but I suspect that the reason that the fungus consumes the plastic slowly is linked to the reason that it is so hard to consume plastic that nothing else does - I suspect the energy it takes to digest it is little more than then energy that is released. Energy Return On Energy Invested (EROEI) is probably dismal.
Little spare energy means it will be slow for the organism to grow and reproduce, as a physical constraint. It’s possible that it could be sped up some, maybe even made to go 10 times faster. But that’ll still be slow as industrial processes go, and it would still require pasteurized/sterilized substrates. In the best case, it would be orders of magnitude more expensive than tossing in a landfill, and would produce compost of almost no economic value (like, mushroom compost is great stuff but mushroom farms only make money on the shrooms, at best compost is a tiny marginal sale).
On a personal level, I get really nervous about engineering microorganisms. I’ve watched too much scifi where humanity arrogantly thinks it can get a handle on unintended side effects, only to create a new plague.
For example, Pestalotiopsis microspora can cause disease in some plants. If we engineer it to grow 10 times faster, we might do an oops on who knows what new species of plants, leading to potentially a brand new crop pathogen, with potentially devastating consequences. And that’s just one example that is easy to think of. We could try to mitigate against that and make an error, or we could totally miss possible dangers and not even try to mitigate for them.