The giant panda’s microbiome isn’t doing it any favors

Panda bears are quite unique in the animal kingdom because they are nearly strictly herbivores yet they are descended from omnivores.  In fact, scientists aren’t quite sure why panda’s made the transition to eating bamboo, because it is a relatively inefficient energy source.  Making matters worse for the panda, its gastrointestinal tract is rather short, and resembles other carnivores, whereas most herbivores have very long gastrointestinal tracts that allow for long retention times for the microbiome to do its work.  This microbiome, of course, breaks down plant material into usable sources of energy for the host and it is critical in all herbivores.  Scientists from China recently investigated the panda’s microbiome, and to their surprise discovered that it too, resembled carnivores’ microbiomes, rather than herbivores’ as one might expect.  They published their results last week in MBio.

The scientists measured the fecal microbiomes of 45 captive pandas over the course of one year, including cubs, juveniles, and adults.  They then compared these microbiome samples with previously reported microbiomes of 54 other species, and wild, rather than captive pandas.  Their first discovery was that the panda’s microbiome was not as diverse as many of these other species, and as our regular readers know, low diversity has been implicated in many diseases in humans.  Next, they found that the panda’s microbiome was actually much more similar to other carnivorous species, especially other bears and tigers, than herbivorous species, and was dominated in Escherichia/Shigella, and Streptococcus, rather than bacteria that are known to degrade cellulose from plant matter, such as Ruminococcaceae, and Bacteroides.  Finally, of particular interest in light of the recent research on the importance of diurnal changes in the microbiome, the scientists noted that the panda microbiome undergoes huge shifts in accordance with the seasons, although they do not speculate as to the effects these shifts may be having.

These discoveries are quite surprising, but they help explain why pandas must eat around 25 lbs. of bamboo every day.  Their microbiomes are just not well equipped to digest this food.  In fact, the lack of cellulose degrading bacteria in pandas’ guts has led some scientists to speculate that pandas are merely living off the cellular contents of each plant cell, rather than the energy dense cellulytic plant cell wall.  Whichever the case, their inefficient digestion certainly is not helping them thrive as a species.

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