Panda gut bacteria can't digest bamboo

Brett Smith for redOrbit.com – Your Universe Online

Think of a giant panda and you’ll probably think of a big bear rolling around in a Chinese forest munching on bamboo all day.

But there’s actually a really good reason why giant pandas always seen to be chewing on bamboo: According to a new study, symbiotic bacteria in the giant panda’s gut is not very effective at breaking down the fibrous plant.

Published in the journal mBio, the new study examined the “carnivore-like” bacteria in the panda’s gut, particularly Escherichia/Shigella and Streptococcus.

“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,” study author Zhihe Zhang, director of the Chengdu Research Base of Giant Panda Breeding in 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.”

Pandas missed the evolution bandwagon

Giant pandas evolved from bears that consumed plants and meat, the study team said, and started consuming just bamboo around two million years ago. Giant pandas get so little nutrition out of bamboo; they must spend up to 14 hours daily eating more than 27 pounds of the plant. However, they can digest only approximately 17 percent of it, with their feces mainly consisting of undigested bamboo fragments. The study team said they had been curious how the animals digest bamboo fiber and draw out nutrients from it.

In the study, researchers used a laboratory process known as 16S rRNA sequencing. They conducted the process on more than 120 fecal samples from 45 giant pandas living at the Chengdu Research Base. Samples were acquired during the spring, summer, and late fall of a single year. Young and adult pandas ate a minimum of 22 pounds of bamboo and bamboo shoots each day, and 1.1 to 1.7 pounds of steamed bread. Overall fecal weights were 22 to 33 pounds each day.

The researchers discovered that despite their diet, giant pandas exhibited extremely low gut microbiota diversity and a general microbial structure that split from non-panda plant-eaters, but was comparable to carnivorous and omnivorous bears. The giant panda gut did not possess plant-degrading bacteria such as Ruminococcaceae and Bacteroides that normally thrive in other herbivores. Instead, giant pandas’ guts were predominated by Escherichia/Shigella and Streptococcus.

The researchers also said panda gut microbiota change with the seasons, possibly due to the lack of bamboo shoots in late fall.

“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,” said study author Xiaoyan Pang, an associate professor in the School of Life Sciences and Biotechnology at Shanghai Jiao Tong University.

The researchers said they plan to further investigate giant panda’s gut microbiota using different scientific techniques.

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