Giant pandas are known for their voracious appetite for bamboo, but these furry mammals are actually meant to eat meat.

That's at least according to a new study published in the journal mBio®, which details how the gut bacteria of giant pandas are not the type for efficiently digesting bamboo. Instead, they boast a carnivore-like gut microbiota predominated by bacteria such as Escherichia/Shigella and Streptococcus, a team of Chinese researchers says.

What's more, this evolutionary mishap doesn't just leave giant pandas chewing and eating bamboo all day, but it may even be leading them down the road to extinction.

"Unlike other plant-eating animals that have successfully evolved, anatomically specialized digestive systems to efficiently deconstruct fibrous plant matter, the giant panda still retains a gastrointestinal tract typical of carnivores," lead study author Zhihe Zhang, director of the Chengdu Research Base of Giant Panda Breeding, China, said in a press release. "The animals also do not have the genes for plant-digesting enzymes in their own genome. This combined scenario may have increased their risk for extinction."

"This result is unexpected and quite interesting, because it implies the giant panda's gut microbiota may not have well adapted to its unique diet, and places pandas at an evolutionary dilemma," added study co-author Xiaoyan Pang.

Giant pandas evolved from bears that ate both plants and meat, researchers say, and started eating bamboo exclusively about two million years ago. These black-and-white bears spend up to 14 hours a day eating as much as 27.5 pounds of bamboo leaves and stems. However, they can digest only about 17 percent of it.

As a result, panda poop is mostly composed of undigested bamboo fragments, leaving scientists wondering how they digest even a little bamboo at all and receive nutrients from it.

To find the answer and better understand panda gut microbiota, Pang and colleagues used a laboratory technique called 16S rRNA sequencing on 121 fecal samples from 45 giant pandas living in Zhang's Research Base. Their results showed that juvenile and adult pandas ate at least 22 pounds of bamboo and bamboo shoots each day, and 1.1 to 1.7 pounds of steamed bread.

Despite their diet, these giant pandas possess extremely low gut microbiota diversity and an overall structure that is unique compared to other plant-eaters, and is actually more similar to carnivorous and omnivorous bears. Unlike other herbivores, the giant panda gut did not harbor plant-degrading bacteria such as Ruminococcaceae and Bacteroides, but rather mostly the bacteria Escherichia/Shigella and Streptococcus.

Panda gut microbiota also varied by season, with late autumn being quite different from spring and summer. The lack of bamboo shoots in late autumn could be an important factor, according to the researchers.

Pang and his colleagues are planning to conduct further research on the matter, combining different scientific techniques to more fully understand the function of the panda's gut microbiota on the animals' nutrition and health.

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