Giant pandas (Ailuropoda melanoleuca) actually harbor carnivore-like gut microbiota predominated by bacteria such as Escherichia/Shigella and Streptococcus, says a team of biologists led by Dr Zhihe Zhang of the Chengdu Research Base of Giant Panda Breeding, China.
Giant panda cub Xiao Liwu and his mother Bai Yun at the San Diego Zoo.
Giant pandas evolved from bears that ate both plants and meat, and started eating bamboo exclusively about 2 million years ago.
The animals spend up to 14 hours daily consuming up to 12.5 kg of bamboo leaves and stems but can digest only about 17% of it; their feces is mainly composed of undigested bamboo fragments.
“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. 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,” said Dr Zhang, senior author on the study published in the journal mBio.
To evaluate the panda gut microbiota, Dr Zhang and coauthors used a laboratory technique called 16S rRNA sequencing.
They analyzed 121 fecal samples from 45 giant pandas (24 adults, 16 juveniles and five cubs) living in the Chengdu Research Base.
Samples were obtained during the spring, summer and late autumn of one year. Juvenile and adult pandas ate at least 10 kg of bamboo and bamboo shoots each day, and 0.5-0.8 kg of steamed bread. Total fecal weight was 10-15 kg per day. The cubs had just fresh milk from their mothers.
The scientists found that despite their diet, they showed extremely low gut microbiota diversity and an overall structure that diverged from non-panda plant-eaters but was similar to carnivorous and omnivorous bears.
The giant panda gut did not harbor plant-degrading bacteria such as Ruminococcaceae and Bacteroides that are typically enriched in other herbivores, but instead was predominated by Escherichia/Shigella and Streptococcus.
Panda gut microbiota also varied by season, with late autumn being quite different from spring and summer.
The researchers are planning a follow-up study combining different scientific techniques to more fully understand the function of the panda’s gut microbiota on the animals’ nutrition and health.
_____
Xue Z et al. 2015. The bamboo-eating giant panda harbors a carnivore-like gut microbiota, with excessive seasonal variations. mBio 6 (3): e00022-15; doi: 10.1128/mBio.00022-15
