It's no wonder that giant pandas are always chewing and eating, say Chinese researchers: their gut bacteria are not the type for efficiently digesting bamboo. The bamboo-eating giant panda actually harbors a carnivore-like gut microbiota predominated by bacteria such as Escherichia/Shigella and Streptococcus, according to new research published this week in mBio®, the online open-access journal of the American Society for Microbiology.

"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," said lead study author Zhihe Zhang, director of the Chengdu Research Base of Giant Panda Breeding, China. "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," said study coauthor Xiaoyan Pang, PhD, MSc, an associate professor in the School of Life Sciences and Biotechnology at Shanghai Jiao Tong University.

Giant pandas evolved from bears that ate both plants and meat, researchers said, and started eating bamboo exclusively about two million years ago. The animals spend up to 14 hours daily consuming up to 12.5 kg (27.5 pounds) of bamboo leaves and stems but can digest only about 17 percent of it; their feces is mainly composed of undigested bamboo fragments. Researchers had been intrigued by how the animals digest bamboo fiber and extract nutrients from it, Pang said.