If you read the article hoping to find out what’s going on here you are:
“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.”
Finding that info on how the fungus does it is why I wanted to read the article, and it was annoyingly buried late in the article after a large number of repetitious paragraphs.
Yes and it still doesn't quite explain things clearly. Mercury is an element so even if it gets broken down into other forms that are less toxic, isn't it still present and not "cleared" as the article claims? Are the new molecules less volitaile/unlikely to revert to their toxic organic forms or more liekly to drain off into waterways?
Organometallic mercury compounds are extremely toxic, so it seems the enzyme is converting the mercury to some inorganic salt with low bioavailability but yeah it appears it becomes less bioavailable but not much else is stated. It’s not removed so I have the same question you do about the possibility of another natural reaction coming along and converting it back
Methyl Mercury is one of the most dangerous forms, because it is volatile and easily absorbed (while liquid metallic mercury is relatively benign). One possibility for the fungus is phenol compounds. They are commonly used by plants to inhibit fungus so the ability to excrete/them would be generically useful to a fungus. Also, mercury phenols are notably quite stable.
And dimethyl mercury is even worse. There's a famous case of a chemist at Dartmouth who died horribly from a single droplet that permeated through a nitrile glove.
I think it would require machinery to dig up the whole field, process the soil and spit it out - which I think is no less expensive than using traditional chemical methods for binding the mercury in stable compounds.
Organic mercury compounds are extremely nasty byproducts of industry. Their badness is largely due to their high bioavailability i.e. they are readily absorbed into our tissues. Inorganic mercury salts, by contrast, tend to have very low bioavailability which limits absorption even in environments with significant background quantities. The toxicity is as much a function of bioavailability as it is presence in the environment. This fungus dramatically changes the bioavailability of mercury compounds in the environment.
There are many highly toxic elements in our environment that are effectively a non-issue due to low bioavailability. In one end and out the other with minimal absorption.
> Mercury is an element so even if it gets broken down into other forms that are less toxic, isn't it still present and not "cleared" as the article claims? Are the new molecules less volitaile/unlikely to revert to their toxic organic forms or more liekly to drain off into waterways?
I have zero specific knowledge, but I can talk about the kind of thing that's generally happening with poisons.
Mercury is extremely toxic. That is probably because various of your enzymes respond to it as if it were a different organic chemical, and use it as a building block in important molecules that they are responsible for building. (It might also be because mercury naturally reacts with important molecules, expelling important functional parts and taking their place. In either case, you're left with defective functional molecules that have useless mercury where they were supposed to have something important.)
Since mercury is an element, it can't be broken down into other forms. But it can be used to build compounds that include mercury atoms. You then have the question of whether these compounds are toxic in the same way that elemental mercury is, whether because they are still (wrongly) recognized as a substitute for something else, or because they still react with proteins to replace important parts of the proteins with mercury atoms, or because the compounds react with something else in the body in a way that ejects their mercury atoms (leaving those atoms free to do their toxic thing).
The goal would be to form mercury compounds that are (1) chemically stable, trapping the mercury atoms; and (2) biologically inert. Ideally those compounds would then either filter through the digestive tract and be excreted in feces, or they'd make their way into the bloodstream, get filtered out by the liver/kidneys, and be excreted in urine.
"Eliminates" in the title seems to contradict the content of the article; the fungus converts organic mercury compounds into less-toxic inorganic compounds.
I see this quite often. Recently I saw a claim that tiger worms can eliminate heavy metals from soil. How do they do that? Do they jump up, and spit the heavy metals onto the garden path? Turns out when you read the paper that the worms just concentrate the heavy metals; to eliminate them, you also have to sift the soil to remove the dead worms.
You can't really get rid of elements in biological systems. So you can only transform the chemicals into a less harmful version or accumulate and store them somewhere where they can't do anything.
Some organo-mercury compounds are dramatically more toxic than elemental mercury, so this is probably quite a bit better than just accumulating them and requiring another method to get rid of the accumulated waste.
In soil it doesn't seem all that useful to accumulate toxic elements, in water I could imagine it being much easier to accumulate them into a non-soluble form that is not bio-available and can be removed much more easily.
Paragraph 3: It sounds unclear whether the elemental mercury accumulates in the fungus, or in the soil, or mostly evaporates. If the fungus is dispersed through the soil, the practical difference between those is limited. The ability of the fungus to prevent uptake of mercury from contaminated soil (by some crops) might be extremely helpful to poor farmers.
BUT - in the context of a water treatment facility, where you might filter contaminated water through a tightly-controlled bit of fungus-filled soil, then actual removal of the mercury seems more plausible. (Admitting that your end-product would probably be closer to "100,000X contaminated soil" than to "nice bottles of shiny stuff".)
Elemental sodium is a violently reactive metal that burns on contact with water.
Molecular chlorine is lethal to pretty much all life.
Sodium chloride, ordinary table salt, is a micronutrient mineral essential to pretty much all life.
Mercury nudges a bit higher up the scale to "best to avoid contact", but the degree to which different sodium compounds are catastrophically lethal, and/or accumulate withing the food chain, differs tremendously.
> Fungi are central to every terrestrial and many aquatic ecosystems, but the mechanisms underlying fungal tolerance to mercury, a global pollutant, remain unknown. Here, we show that the plant symbiotic fungus Metarhizium robertsii degrades methylmercury and reduces divalent mercury, decreasing mercury accumulation in plants and greatly increasing their growth in contaminated soils. M. robertsii does this by demethylating methylmercury via a methylmercury demethylase (MMD) and using a mercury ion reductase (MIR) to reduce divalent mercury to volatile elemental mercury. M. robertsii can also remove methylmercury and divalent mercury from fresh and sea water even in the absence of added nutrients. Overexpression of MMD and MIR significantly improved the ability of M. robertsii to bioremediate soil and water contaminated with methylmercury and divalent mercury. MIR homologs, and thereby divalent mercury tolerance, are widespread in fungi. In contrast, MMD homologs were patchily distributed among the few plant associates and soil fungi that were also able to demethylate methylmercury. Phylogenetic analysis suggests that fungi could have acquired methylmercury demethylase genes from bacteria via two independent horizontal gene transfer events. Heterologous expression of MMD in fungi that lack MMD homologs enabled them to demethylate methylmercury. Our work reveals the mechanisms underlying mercury tolerance in fungi, and may provide a cheap and environmentally friendly means of cleaning up mercury pollution.
The technical word for this is chelation / chelating. I've seen it used with respect to iron, lead, mercury and cadmium. When a substance can render one inert it generally does with the others as well.
There are a number of pltants, roots, and fungi that do this. I was looking into this yesterday with respect to curcuma, as the region i am currently visiting is known to be contaminated with lead and everyone likes to eat fish from the nearby river. I came across this article which shows solid evidence that curcuma can also remove lead accumulation from the bodies of mammals. https://pubmed.ncbi.nlm.nih.gov/31489882/
Mushroom hunters are often told to avoid picking in spots contaminated by industry, notably due to the bioaccumulation of heavy metals in the environment, so even non-engineered fungi hold promise in remediation strategies. In part this is attributed to the wide spread of their mycelium.
But as there are still early years in studying the application of these organisms in soil remediation, a whole-systems environmental analysis would seem like a logical next step for these Maryland researchers' upcoming field experiments in China. For instance, although the authors indicate that corn plants immediately grown in the vicinity were absent in Hg, what is the impact on insects that consume (and are actively parasitized by) this fungus, and the bird species a trophic level above, especially after the engineered increase in Hg uptake?
Likewise, how stable are the genes produced by the researchers for the artificially increased mercury uptake (against horizontal gene transfer over time to soil microbiota, e.g. Agrobacterium, or to plant-fungus horizontal gene transfer events directly)?
I am skeptical: this fungus cannot possibly sieve through all the contaminated soil, even on a long timespan, so plants' roots would still be able to absorb mercury. Even considering that it colonises the roots themselves, it is not a tight layer around the roots that prevents any mercury from getting in.
I bet in a hundred years we're using genetically modified fungus to remove all sorts of contaminants from the environment. There's already mushrooms that can feed off radiation.
My understanding of fungus, a side interest, is that you probably don't need to genetically modify them. There is probably a fungus already doing what you want somewhere. You just need to find it. Fungus are amazing, and we understand really nothing about them.
Exactly this, we should to be careful with introducing any modified spieces at scale before we understand the existing ecosystem and before we kill it with some invasive mutants.
I don't think it matters much if something is genetically engineered or not. Normal (unmodified) invasive species already cause a lot of damage to ecosystems. From the point-of-view of the damaged ecosystem, it doesn't matter if the invader is GE or perfectly natural; it still doesn't belong there.
I think something that could accumulate lead would be highly useful, given we've spent much of the last century indelicately vapourising it over everything.
As others have pointed out, the phys.org link is quite vague. I went to the cited article at https://www.pnas.org/doi/10.1073/pnas.2214513119, but there is a paywall. Yet another tedious paywall. It's too early in my day for that.
But at least the pnas page has a link that gets you to a PDF of supplemental material from that site, which might be of help to those who would like to know about the Hg compounds in question here.
I do wish the phys.org article had chosen to feature the word "compounds" in the title, and perhaps also the word "transform" instead of "remove". But that wouldn't be as eye-catching, and it seems that phys.org is all about catching eyes, lately.
“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.”
Finding that info on how the fungus does it is why I wanted to read the article, and it was annoyingly buried late in the article after a large number of repetitious paragraphs.