Moelselio Schaechter and Stanley Maloy consider an old, and increasingly good question in the Small Things Considered blog:
How often have you heard it said, or seen it stated in writing, that we carry ten times more microbial cells than cells of our own? We don’t dispute this figure, at least not as a ballpark estimate. But we were curious to find out where it came from. The paper that seems to be quoted most often in this regard is Microbial Ecology of the Gastrointestinal Tract by Dwayne Savage in the Annual Review of Microbiology, 1977, 31:107-33….
Just how authoritative is that? References to experimental work? None are given….
Note, however, that we take leave from a good portion of our intestinal microbiome every day, the lucky among us with satisfying regularity. So, the ratio fluctuates daily. No big deal, but let’s qualify the ten-to-one mantra by saying “estimated.” To say the least.
(Thanks to investigator E.C. Doane for bringing this to our attention.)
BONUS: This ratio will be on display, subtly, in “The Bacterial Opera”, which will premiere on September 30 as part of the Twentieth 1st Annual Ig Nobel Prize Ceremony.