A common fungus eliminates toxic mercury from soil and water: researcher
phys.org
phys.org
“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.
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.
Was it outcome of that compound being eaten by fungus? (some process that resulted in energy extraction?)
In such case reverse strategy is possible but less likely
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.
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.
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.
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.
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".)
> 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.
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/
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)?
The fungus collects stuff from the dirt; the plant trades those nutrients for sugars produced with sunlight.
First I should understand what exactly is the expectation to call soil "decontaminated".
Does anyone know if Miyazaki based the fungus forest element of his story on known science?
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.