Miraculous Mushrooms Mitigate Mercury Menace

I never hear people proposing policies for cleaning up chemical pollution. I don’t know whether that’s because the ways to do it are less widely known, or because the issue is just less urgent and less in-vogue than climate change, or a secret third thing. Regardless, it’s an issue that I think is important, and (to the great shock of nobody), a problem that I think is best addressed using the abilities of organisms like plants, fungi, and bacteria.

That’s why I was happy to see this research, showing that not only can a particular fungus clean up mercury, in soil and in water, but we can apparently enhance its ability to do so:

“This project, led by Dr. Fang, found that Metarhizium stops plants from taking up mercury,” said St. Leger. “Despite being planted in polluted soil, the plant grows normally and is edible. What’s more, the fungus alone can quickly clear mercury from both fresh and saltwater.”

Metarhizium is a nearly ubiquitous fungi, and previous work by the St. Leger laboratory had shown that it colonizes plant roots and protects them from herbivorous insects. Scientists have known that Metarhizium is often one of the only living things found in soils from toxic sites like mercury mines. But no one had previously determined how the fungus survived in mercury polluted soils, or if that had implications for the plants the fungus normally lives with.

St. Leger and other colleagues had previously sequenced the genome of Metarhizium, and Fang noticed that it contains two genes that are very similar to genes present in a bacterium known to detoxify, or bioremediate, mercury.

For the current study, the researchers ran a variety of laboratory experiments and found that corn infected with Metarhizium grew just as well whether it was planted in clean soil or mercury-laden soil. What’s more, no mercury was found in the plant tissues of corn grown in polluted soil.

The researchers then genetically modified the fungi, removing the two genes that were similar to those in mercury remediating bacteria. When they replicated their experiments, modified Metarhizium no longer protected corn plants from mercury-laden soil, and the corn died.

To verify that the genes were providing the detoxifying qualities, the researchers inserted them into another fungus that does not normally protect corn from mercury. The newly modified fungus performed like the Metarhizium, protecting the plants from mercury-laden soil.

Microbiological analyses revealed that the genes in question expressed enzymes that break down highly toxic organic forms of mercury into less toxic, inorganic mercury molecules. Lastly, the researchers genetically engineered Metarhizium to express more of the detoxifying genes and increase its production of the detoxifying enzymes.

In their final experiment, the researchers found they could clear mercury from both fresh and salt water in 48 hours by mixing in Metarhizium.

The next step will be to conduct experiments in the field in China to see if Metarhizium can turn toxic environments into productive fields for growing corn and other crops. Current methods of remediating polluted soils require toxins to be removed or neutralized from entire fields before anything can be planted. That can be very expensive and take a long time. But Metarhizium simply detoxifies the soil immediately surrounding the plant roots and prevents the plants from taking up the toxin.

“Allowing plants to grow in mercury-rich environments is one of the ways this fungus protects its plant home,” St. Leger explained. “It’s the only microbe we know of with the potential to be used like this, because the bacteria with the same genetic capabilities to detoxify mercury don’t grow on plants. But you can imagine simply dipping seeds in Metarhizium, and planting crops that are now protected from mercury-rich soils.”

In addition to its potential as a cost-effective tool for reclaiming polluted lands for agriculture, Metarhizium may help clear mercury from wetlands and polluted waterways that are increasingly threatened by mercury pollution as climate change and melting permafrost accelerates the release of the toxic metal into soils and oceans.

This seems like great news! What’s more, if the claims made here are born out in future research, then it means that with the right preparation, even toxic soil could grow food that’s safe to eat. I honestly never would have thought of that, and the implications are fascinating, both as an activist, and as a science fiction writer. This is one of those times where I feel like I could see really amazing biotech innovations in my lifetime, that could help in pretty unambiguous ways, like rendering pollution harmless.



  1. says

    That is an extremely interesting finding. I do wonder if other heavy metal pollutants like Cadmium and Vanadium cal also be mitigated this way, either by this organism or some other one?
    It looks like edible stuff could be grown safely atop old waste dumps etc. which would be of some help. Or firewood could be grown on toxic sites without the fear that the resulting ash would contain toxic heavy metals.

  2. sonofrojblake says

    I’ve worked on Mercury-laden sites – to the point that I’ve walked round a patch of concrete we were using as a car park, pipetting up free mercury that was sweating out of the surface in the summer sun.

    This sounds good in principle, but where does the Mercury *go*? “less toxic inorganic mercury molecules” isn’t”no mercury”, which is the ideal.

    For a substance that used to be marketed in kids toys until well into my twenties, it’s remarkably Persistent and horrible stuff.

  3. says

    It’s a valid question.

    I think that for some areas, the default approach will be to just prevent anyone from using the contaminated sites, and basically hope nature buries it, kinda like the Red Forest in Ukraine.

  4. sonofrojblake says

    prevent anyone from using the contaminated sites

    Rather the point of the article seems to be allowing people to use the contaminated sites for growing food. They’re just patting themselves on the back that the food grows at all and doesn’t kill you if you eat it. Keeping people the heck away from it is a valid response. What would worry me is the concept of repeatedly ploughing it up and turning it over and planting in it. When we put a spade in the ground to lay foundations for a new plant near the bit I referred to above, there was free mercury running in the soil in rivulets. At that point the whole job stopped and the area was cordoned off until we could arrange remediation for the limited area we needed – it cost tens of thousands of the project budget, which fortunately I’d accounted for due to the aforementioned experience. But the mercury had already been the for decades. Hoping nature buries it isn’t really a sustainable solution.

  5. says

    Well, yes – that’s the use they tested. That’s not what I personally would do.

    But yes, I agree that a more active approach would be better.

  6. says

    I think if it was me, I’d want to see if we could use fungus like this to grow a layer of “turf” that fixes the heavy metals, and could then be rolled up, processed and stored somewhere. I think trying to farm contaminated soil like that would be a death sentence for the workers, unless decontamination (with adequate protection) was the “crop”

  7. John Morales says

    Phytomining (a form of phytoremediation) is an active area of research.

    (Yes, I know fungi are not plants)

Leave a Reply

Your email address will not be published. Required fields are marked *