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article imageOp-Ed: Giant 2500-year-old fungus raises a lot of questions

By Paul Wallis     Jan 9, 2019 in Science
New York - How does an ancient, gigantic fungus become so genetically stable that its level of mutation is virtually non-existent? How did this huge thing manage to live for 2500 years? Answer those questions, and you have some Big Biology to work with.
Researchers seem to have hit the jackpot in fungal mysteries with this monster. The giant fungus (Armillaria gallica) is in Michigan, and covers a whopping 180 acres. It was first discovered in the 1990s, pre-genome technology, and its size and age were underestimated. New studies have found a true monument to fungi, a fungal empire with some truly astonishing characteristics.
That’s no minor achievement. Fungi are primary drivers for the entire global ecology, breaking down organic materials and recycling everything. To find a big, super-stable fungal system like this is quite like a Rosetta Stone in mycology, a series of messages to be understood. This particular fungus could hold keys to a whole range of genomic science aspirations, from curing cancer to fundamental ecological research. See the Royal Society paper for the technical information.)
There’s more than meets the eye to fungi, in more ways than one. Mushrooms are the flowering bodies of fungi, but the rest of the organism is a complex of substrate organic materials, covering large areas. How this vast fungus grew so big is a major issue, and it comes with some truly stunning problems to solve:
1. The fungus doesn’t replicate very often, yet it’s managed to cover 180 acres? Is this another case of a low speed (in this case downright laidback) reproductive cycle delivering longevity?
2. There are far fewer mutations in the fungal genome than would be expected from such a massive organism. This relates to a thing called “homozygosity”, which is usually associated with inbreeding of organisms, which in turn is supposed to be bad for them. Not in this case, apparently?
3. Now consider the fact that this organism has been around for 2500 years, and still has a lower rate of mutation. What sort of biology and ecology support that situation?
4. This is not a passive organism. Fungi can break down dead wood, and attack weakened trees. This particular fungus would also need to have been very successful at these core functions to spread so consistently, over such a long time.
The environment
This particular Armillaria gallica is definitely located in a sweet spot, ecologically. It’s in the middle of a pine plantation, great for a wood-digesting fungus, and Michigan is right in the southern end of the old coniferous Boreal forest which used to cover North America.
The fungus isn’t located in the toxic hell zone of Michigan for pollution, and is in a fairly typical, almost near natural area near the Paint River, with obviously good water resources. This is promised land country for fungi, good soil, plenty of food, and lots of water. If you were a fungus planning a holiday, this is where you’d go.
So – Is this a sort of idealized giant fungus in an idealized location? Ah, um, … Maybe not. The “maybe not” is based on a very slow replication level. In the last 2500 years, a lot will have happened in this environment. Forests don’t grow evenly. They can be infested with pests, invasive plants, etc., too. Dry spells, in particular, can affect fungi pretty drastically. Conifers are also pyrogenic, meaning they need regular fires for them to reproduce.
So if you’re a savvy fungus, you don’t go nuts with your replication. You do it at optimum times, and use your ability to go dormant in the bad times. At least a few seasons and events will be negative over any given decade or so. 250 decades later, this Armillaria gallica has obviously got the routine down to perfection.
Genetic issues, and plenty of them
The low level of mutation has a lot of issues attached:
1. Have there been no environmental genetic impacts to deliver at least occasional mutations? Not many, apparently, and if so, they’ve obviously been shut down, method unknown. The Armillaria are known for their “pleiomorphic” characteristics (ability to change shape and size), so does that have something to do with this genetic high fidelity? An organism of this level of versatility would be quite able to be selective, as researchers speculate, and maintain gene integrity.
2. If Armillaria gallica can maintain such genetic stability, how? Does it have a gene stabilizing mechanism, or just better gene management than practically everything else on Earth? You can see why this has the genome guys fascinated. If the fungus has solved the dangerous mutations issue, it’s a major deal.
3. To make the genetic mystery even more baffling - The “inbreeding” effect is having the exact opposite effect to the usual outbreaks of lethal genes that inbreeding causes in other organisms. Why not in this case? This fungus simply doesn’t have anything like the range, let alone the incidence, of genetic issues of other organisms.
4. The very slow growth rate may be the key. The longest lived organisms on Earth have continuous growth over very long periods of time, usually combined with a slow metabolism. Fungi are a bit different. Fungal enzymes are powerful chemistry, and certainly not slow. In terms of biological dynamics, they’re arguably more active than most other organisms unless actually dormant.
5. The observed information still doesn’t answer how a fungus attains a mass of 8 x 10 to the 5th power kilograms, over such a huge area, unless sporulation is basically a colonizing process rather than random growth. Colonizing would block out competitors, and monopolize local resources. Could be the fungal answer to ant super colonies, virtually indestructible, and functionally immortal. Great survival tactic, for sure.
6. Evolutionary breakthrough? Mastering the basic weirdness of genetics and turning yourself in to something bigger than a few blue whales requires some good evolutionary practices.
Fungi are among the oldest organisms on Earth, so it may be they’ve solved the rogue genes problem. Older, highly evolved species are typically tougher than hell, highly adaptive, and very well able to handle Nature’s moods.
This fungus could be the blueprint for a whole new perspective on so many biological things it’s almost ridiculous. Go to the fungus, thou sluggard, consider her ways, and be wise. Makes sense, doesn’t it?
This opinion article was written by an independent writer. The opinions and views expressed herein are those of the author and are not necessarily intended to reflect those of
More about mycology, Armillaria gallica, fungal genetics, low mutation in fungi, fungal homozygosity
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