Mucor racemosus May Protect the Gut From Radiation

Mould is not normally something you would want growing inside your body.

Yet Mucor racemosus may offer a good reason to reconsider that instinct.

A new study published in PNAS suggests this symbiotic fungus, which resides in the human gut, could help protect us against radiation.

That may seem difficult to accept, but it is not the first example of fungi behaving in unusual ways around radiation.

Radiation-resistant fungi and Mucor racemosus

Several types of radiation-resistant fungi are known, including species able to withstand X-ray exposure of up to 200 times the dose that would be fatal to humans.

Then there are radiotrophic fungi, which harness radiation as an energy source – such as the extraordinary fungus thriving amid the radioactive ruins of the Chernobyl Nuclear Power Plant.

M. racemosus has a different radiation-related talent, though it is no less remarkable.

Scientists in China found that the fungus can protect its host from radiation through two distinct mechanisms. Their results indicate that M. racemosus could be a helpful inhabitant of the gut.

In radiation-exposed mice, animals given M. racemosus lost less weight and showed lower levels of inflammation and oxidative stress than control mice that did not receive the fungus. This indicates that M. racemosus had a radioprotective effect in the treated animals.

The protection became stronger when the scientists pre-adapted the fungus to the low-oxygen environment found in the gut.

Germ-free mice – animals raised without microorganisms – also displayed fewer signs of radiation damage after receiving the fungus than control animals. This suggests that M. racemosus can help defend against radiation harm independently of the host microbiota.

"These results demonstrate that M. racemosus directly alleviates radiation-induced intestinal injury in mice," the researchers explain.

How Mucor racemosus protects against radiation

Further tests involving irradiated intestinal cells and mice identified three amino acids made by the fungus that may account for its radioprotective properties: L-glutamic acid, L-aspartic acid, and DL-lysine.

The researchers say these three amino acids directly support DNA repair and the recovery of intestinal tissue following radiation exposure.

However, that is not the fungus's only protective strategy.

Methylthioadenosine (MTA), another chemical produced by the fungus, also has an important radioprotective function, although it does not directly repair radiation damage in the way the three amino acids do.

Rather, MTA produced by M. racemosus appears to regulate the growth of a bacterium known as Limosilactobacillus reuteri. It also reprogrammes the bacterium to produce more methionine, a chemical whose elevated levels seem to enhance radiation protection.

Fermented cheese and therapeutic potential

To assess the therapeutic potential of M. racemosus, the team gave irradiated mice cheese fermented with the fungus. Compared with mice fed cheese without the fungus, these animals had less intestinal inflammation, stronger intestinal barrier integrity, and lower systemic markers of inflammation.

Much more research is required before anyone can conclude that M. racemosus should form part of everybody's balanced diet. However, the researchers note that the fungus already occurs naturally in, or is added to, certain fermented foods, and is approved by the FDA for dietary use.

Nevertheless, M. racemosus may pose a health risk to immunocompromised people. Care is therefore needed when determining whether the fungus – and perhaps some of its companions – could find a place in the food pyramid or medicine cabinet.

"More broadly, these findings establish filamentous fungi as underappreciated yet influential agents in the microbiota–host axis," the researchers write, "with potential applications for mitigating radiation-induced damage and other health conditions."

The findings are reported in PNAS.

This article was fact-checked and edited by Rebecca Dyer. Although we take pride in our process, we are only human. If you notice an error, please let us know.