LAUSR

Hibernation is a mammalian strategy that uses metabolic plasticity to reduce energy demands and enable long-term fasting. Fasting mitigates winter food scarcity but eliminates dietary nitrogen, jeopardizing body protein balance. Here, we reveal gut microbiome–mediated urea nitrogen recycling in hibernating thirteen-lined ground squirrels (Ictidomys tridecemlineatus). Ureolytic gut microbes incorporate urea nitrogen into metabolites that are absorbed by the host, with the nitrogen reincorporated into the squirrel’s protein pool. Urea nitrogen recycling is greatest after prolonged fasting in late winter, when urea transporter abundance in gut tissue and urease gene abundance in the microbiome are highest. These results reveal a functional role for the gut microbiome during hibernation and suggest mechanisms by which urea nitrogen recycling may contribute to protein balance in other monogastric animals. Description While they sleep Hibernation has evolved to remove animals from seasonal periods that are especially challenging for survival. Despite this protective feature, hibernation poses its own challenges because of the extensive fasting period. One particularly challenging aspect is the lack of dietary nitrogen, which can lead to protein imbalance. Regan et al. looked at gut microbiome activity in hibernating thirteen-lined ground squirrels and found that symbionts recycled nitrogen from urea into their own metabolites, which were then incorporated by the squirrels, allowing them to maintain protein balance (see the Perspective by Sommer and Bäckhed). These results reveal the importance of the gut microbiome to hibernation and suggest that gut microbes could play such a role in other species. —SNV Gut microbiome–mediated urea nitrogen recycling helps ground squirrels survive prolonged fasting during hibernation.