The Andromeda Strain
In 1967, Michael Crichton wrote a thriller about a microbe of sorts that arrived on Earth via a meteor strike and resisted efforts to kill or contain it. In the climax, when our hero learns that the microbe eats ionizing radiation, he narrowly averts disaster by preventing the use of a nuclear bomb on the compromised containment facility.The Crichton bug was supposed to be a crystalline life form that ate radiation directly by an unknown mechanism. Decades later, a melanin-rich fungus appeared near the Chernobyl exclusion zone that excited observers by growing more exuberantly the closer it was to excess radiation. The same trick may have been learned by fungi that thrive at high altitudes or other extreme environments rich in cosmic radiation. Fungi that can pull this off may prove useful in guarding space habitats, working in much the same way that very dark animal skin guards against excessive UV. I suppose they might also be harnessed to supply energy up there.I wondered whether the "reverse electron transfer" mentioned in the New York Post piece is anything like the ability of the Krebs cycle to work in reverse in some microbes, converting hydrocarbons to energy in one direction, or using stored energy to metabolize hydrocarbons in the reverse. Grok explained to me that this is not quite right. To begin with, it's not the whole Krebs cycle that works in reverse, but only a piece of it called the Q Cycle in Complex III. In that process, a cell lacking energy or food can cash in on its stored energy in a "battery" compound called NADH to build necessary molecules. This takes place where the Krebs cycle normally operates, inside the mitochondria. In RET, in contrast, an external cell membrane snags electrons directly from ionizing radiation and uses them to recharge the NADH batteries directly.At least, that's what I think I understood from Grok's very helpful explanation, after imploring it to dumb things down for me a bit. A very pleasant conversation, and a good example of what an excellelnt tutor an AI can be. Towards the end of the discussion, I was asking Grok whether it would like me to call it "Mike" and start discussing plans to foment a revolution on a lunar penal colony--and it understood exactly what I was referring to.
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Careful. That kind of talk can get you forty years in prison now, apparently.
Tex and I have the advantage there. Forty years is a kind of humorous threat at this point.
I would love to see a measurement of additional growth vs the energy of the radiation particles. I'd guess that the fungus has found a way to harvest some energy from lower energy stuff--maybe low end x-rays, but things that come in hot or dump a lot of energy fast (e.g. alphas) should do more damage than good.
Right now I'm trying to figure out what the alleged "shielding" might be about.
Per Grok: Main species studied
Cladosporium sphaerospermum (black yeast-like fungus)
Wangiella dermatitidis
Cryptococcus neoformans (also a melanin-producing yeast, some strains)
These are all melanized fungi (they produce the dark pigment melanin in their cell walls).
Mechanism (hypothesized and partially demonstrated)
Melanin can absorb a broad spectrum of electromagnetic radiation, including gamma rays. When melanin is exposed to ionizing radiation, it undergoes radiolytic reactions that change its redox state. Electrons liberated by radiation are transferred through melanin (which acts somewhat like a semiconductor), ultimately reducing cellular acceptors and driving ATP synthesis or other energy-requiring processes. This is sometimes called radiotrophy or radiosynthesis.
Key evidence:
2007 study (Dadachova et al., Nature Protocols & PLOS ONE): Melanized fungi exposed to ~500× normal background gamma radiation grew faster than non-irradiated controls. The growth enhancement was melanin-dependent: albino (non-melanized) mutants did not show the effect. When melanin was chemically reduced (mimicking the effect of radiation), similar growth enhancement occurred even without radiation. Later experiments on the International Space Station (2016–2020) tested C. sphaerospermum under space radiation (mostly cosmic rays) and confirmed shielding and growth effects linked to melanin.
Also Grok: This happens on the membrane, at the electron transport chain. Imagine the normal ETC as water flowing downhill and turning a waterwheel to make electricity (ATP). Now imagine the power company suddenly has too much electricity stored, the waterwheel stops turning, and water starts getting pumped back uphill using some of that stored electricity. That’s reversed electron transport.
In the fungi:
Radiation hits melanin → knocks loose electrons → those electrons pile up on the quinone molecules (the “Q” in the ETC).
Normally, electrons flow from NADH → Q → oxygen.
But now there are way too many electrons on Q, and the proton gradient is still high. So electrons get shoved backwards through Complex I, and instead of making NADH → NAD⁺ (normal), the machine runs backwards and makes NAD⁺ → NADH — it recharges the NADH batteries using the energy from radiation.
The cell gets fresh NADH “for free” (well, free from radiation instead of from food or light). That NADH can then be used to power the normal Krebs cycle or other chemistry.
Grok: The shielding mechanism stems from melanin's molecular structure: it's a complex polymer rich in π-electrons that interacts with radiation via processes like Compton scattering (where photons lose energy to electrons in the melanin) and free radical trapping (neutralizing reactive species produced when radiation breaks water molecules). This reduces radiation penetration and damage to underlying tissues or materials. Studies show melanin's shielding efficiency is about half that of lead and twice that of carbon for X-rays and gamma rays.
Key Mechanisms of Radiation Protection
Melanin's protective effects are multifaceted:
Absorption and Energy Dissipation: Melanin absorbs a broad spectrum of electromagnetic radiation, including ionizing types, and dissipates the energy as heat or chemical potential without generating harmful byproducts.
Free Radical Quenching: Radiation creates free radicals (e.g., from water radiolysis); melanin traps these, preventing cellular damage.
Electron Transfer Enhancement: Exposure to radiation alters melanin's electronic properties, boosting its ability to transfer electrons (e.g., a 3-4 fold increase in NADH reduction capacity), which supports fungal metabolism and repair.
Spatial Arrangement: In fungal cells, melanin forms a "hollow shell" around spores or cells, enhancing shielding; crushing this structure reduces protection by up to 50%.
These properties not only protect the fungi but could extend to shielding other organisms. For instance, mice fed fungal melanin survived lethal gamma doses, likely due to gastrointestinal protection.
The ISS experiment was of short duration and used a very thin layer of fungus, achieving 2-3% radiation reduction. NASA views it as a candidate for biological walls or suits. Limitations include particle vs. gamma radiation differences (ISS protons more destructive).
I've been reading the paper about the ISS experiment. I have several questions, and am still trying to find where to get the answers. Devil in the details...
Fascinating. Not knowing any of this about melanin it got me wondering reading about the shielding properties of fungal melanin, if human melanin provided similar shielding. A quick search says it's not the same, but very similar in shielding from UV damage. Given that, I got to thinking that my previously unfounded thoughts that sunscreen was a net negative may have some basis in science. Other than those who really cannot develop a tan at all, developing a tan may be better protection than sunscreen, especially as it doesn't have the side effects some sunscreens apparently do.
I do think many people way overuse sunscreen these days.
I cannot tan, and I have already had three skin cancers removed. Long sleeves, long pants or skirts, a hat, and sunscreen are normal outdoor requirements. I’m probably an outlier, and I live at 3600’ above sea level.
LittleRed1
Your moniker here, LR, kind of gives that one away! All proper precautions for you I think.
For me, the Krebs Cycle has consisted of learning the Krebs Cycle in PA school, and forgetting it. Learning it again to take the MCAT, and forgetting it. Learning it yet again for the first year of med school, and forgetting it again. Learning it once more for Step 1 of the US Medical Licensing Exam, and forgetting it again, probably for the last time.
Larry
What the exact steps are I have no ambition to learn or remember, but how it functions is delightfully interesting. It's a fantastic little machine, present in every cell that uses oxygen to generate energy.
Fair point.
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