Carbon recycling in nature
Regan’s team focused on the ground squirrel, a hibernator from the marmot family (not the urban squirrels that populate Montreal’s parks). The scientists uncovered a remarkable survival strategy: the squirrels’ gut microbes salvage carbon from urea, a waste product usually flushed out in urine.
Instead of being excreted through the bladder, the squirrels' urea is rerouted to their intestines. There, microbes equipped with enzymes not found in vertebrates break it down and repurpose the carbon to create acetate.
To trace this process, the researchers injected ground squirrels with urea containing carbon-13, an isotope that rarely occurs naturally in the organism and is therefore easily tracked in the body.
“We found that gut microbes extracted carbon from the urea and converted it into acetate, a critical biomolecule which the squirrels then absorbed and used during hibernation,” Regan said. “When we eliminated the microbes using antibiotics, the carbon recycling process stopped dead.”
Previous research by the team found a similar process involving nitrogen, an essential element for protein production that is similarly cut off during hibernation. Nitrogen, which is also present in urea, is reabsorbed and reused to build proteins, helping to preserve muscle and vital functions.
Could humans benefit?
Regan believes these findings could have implications for humans. Urea nitrogen recycling is well-documented in ruminants such as cows and camels, whose digestive systems are specifically adapted to collaborate with microbes.
“Humans theoretically have the same capacity,” Regan explained. “Studies from the 1990s show that we have the necessary microbes and ‘biological infrastructure,’ including cellular transporters, enzymes and metabolic pathways. But we’re far less efficient than hibernators.”
He noted that squirrels gradually ramp up their recycling ability during hibernation, peaking just before they wake in the spring. Their physiology therefore changes to maximize this life-sustaining process.
A solution for space travel?
Humans begin losing muscle mass and strength—a process known as sarcopenia—by age 30 or 40. Poor nutrition, poor protein balance and some illnesses can accelerate this process.
So can spaceflight. Muscles deteriorate rapidly in microgravity. Astronauts must train for several hours per day to limit the damage, and recovery can still be slow.
“Hibernators have evolved near-total resistance to muscle atrophy,” Regan said. “Understanding how they recycle nitrogen so efficiently could yield new ways to protect muscle mass in humans, whether on Earth or in space.”
The takeaway? Survival isn’t always about finding more resources. Sometimes, it’s about recycling what we already have.
