The gut microbiome determines the body’s response to seasonal dietary shifts in the giant panda by synchronizing the body’s peripheral biorhythms that modulate metabolism, new research from China shows. The findings provide insights on the link between the gut microbiome and phenotypes such as body mass and fat metabolism, providing new avenues to improve fitness.

The new study was published on January 18 in the journal Cell Reports in an article titled, “Seasonal shift of the gut microbiome synchronizes host peripheral circadian rhythm for physiological adaptation to a low-fat diet in the giant panda.” This study that clarifies the link between seasonal changes and the body’s adaptive responses, deepens our understanding of host-microbe interactions in wild animals.

Butyrate synthesized by the panda’s gut microbiota during shoot-eating season increases circulating phospholipids, fat storage and body weight through synchronized expression of the circadian gene Per2 in the liver (Huang G, et. al., Cell Reports, 2022).

Giant pandas stay chubby and healthy on a diet consisting solely of bamboo shoots, leaves and stems. Pandas prefer shoots, which are the most nutritious, followed by leaves and stems. In the new study, a team led by researchers at the Institute of Zoology at the Chinese Academy of Sciences in Beijing shows that the bear’s gut microbiome undergoes seasonal changes allowing it to store more fat and gain more weight when nutritious bamboo shoots are available in the spring. This shift in its gut microbiome compensates for the lack of nutritious shoots during other seasons.

“This is the first time we established a causal relationship between a panda’s gut microbiota and its phenotype,” said Guangping Huang, PhD, scientist at the Institute of Zoology, Chinese Academy of Sciences (CAS) and first author of the paper. “We’ve known these pandas have a different set of gut microbiota during the shoot-eating season for a long time, and it’s very obvious that they are chubbier during this time of the year.”

Huang said, “Causal research of host phenotype and gut microbiota in wild animals is just beginning. Identifying what bacteria are beneficial for animals is very important, because one day we may be able to treat some diseases with probiotics.”

Fuwen Wei, PhD, a scientist at the CAS Institute of Zoology, has been studying wild giant pandas of the Qinling Mountains in central China for decades. Wei said, these wild pandas have a significantly higher level of a bacterium called Clostridium butyricum in their gut during the shoot-eating season.

The team simulated seasonal changes in the panda’s gut microbiome in germ-free mice through classic experiments involving fecal microbiota transplantation (FMT) to explore whether changes in the gut microbiota could affect the panda’s metabolism. The scientists fed mice that were transplanted with the panda’s microbiota from the shoot-eating season or the off season, a bamboo-based diet that reflected the panda’s diet.

“For endangered and vulnerable wild animals, we can’t really run tests on them directly. Our research created a mouse model for future fecal transplant experiments that can help study wild animals’ gut microbiota,” said Huang.

Although mice in both groups consumed the same amount of food, the researchers found mice transplanted with the panda’s gut microbiota from the shoot-eating season stored more fat, had higher levels of phospholipids in the circulation, and gained more weight than mice transplanted with the panda’s gut microbiota from the leaf-eating season.

To explore the underlying mechanism that causes this effect of the gut microbiome on the metabolism, the researchers conducted metabolomics studies on liver and plasma samples from the mouse models.

Through a multi-omics approach followed by experimental validation the researchers found that butyrate produced by the gut microbiota, particularly C. butyricum, affected the expression of key circadian genes such as Per2, leading to fluctuations in circulating phospholipids, lipid synthesis and storage. This indicates, seasonal changes in the panda’s gut microbiota synchronizes the bear’s peripheral circadian rhythm that in turn modulates lipid metabolism.

This shift in the composition of the gut microbiota is not unique to giant pandas. Certain species of monkeys have different gut microbiota in summer when fresh leaves and fruits are available compared to their gut microbiota in winter when they must subsist on tree barks. The Hadza, or Hadzabe, a Tanzanian indigenous ethnic group who are modern day hunter-gatherers also show a similar seasonal change of their gut microbiomes.

In future studies, the team plans to chart how other members of the panda’s gut microbiome affect the animal’s metabolism and health.