Microbiome Myth Debunked: Counting Bacteria in Our Gut = A New Ratio

microbiome gut microflora nature weizmann us nih luckey

As reported in Nature, new data has completely contradicted the universally accepted rule than the number of bacteria within our guts greatly outnumbers the number of our own cells.Why?

weizmann_microbiome_nih_luckey_cells_microbiota_gi_tractThe long standing belief in Biology has been solid on the ratio of Microbes, viruses and human cells within our bodies. However, researchers Ron Milo and Ron Sender at the Weizmann Institute of Science in Rehovot (Israel) and Shai Fuchs at the Hospital for Sick Children in Toronto, Canada.

This 10:1 ratio of bacteria to human cells actually originated from a Microbiologist, Thomas Luckey, in 1972, and has persisted ever since to be a common belief in even the most literate of scientists.

Concerned over the paradigm this ratio had created within the Biological community (particularly in the emerging field of Microbiomics), in 2014 researchers at  the US NIH decided to flag (as reported in the Boston Globe).


An infographic from the Biotech Seres Health now depicts potentially outdated Data on the Human Microbiome – although clarity on this issue has yet to be achieed (Source: Seres Health)

Counting Cells‘ was an investigational review by the Weizemann and Canadian researchers. And they identified that a flaw in Luckey’s reasoning, which extrapolated the number of bacteria in the whole Gastrointestinal tract (1014 cells) from the mouth to the rectum was proportional to the amount in a gram of faeces (1011 cells).

However, the colon approximates 40% of the GI tract and is in fact the habitat for the majority of the Microbiota. And perhaps, the team concluded, Luckey had miscalculated the actual number of bacteria within fecal matter, which even then could change with each bowel movement. Lovely!

The numbers are similar enough that each defecation event may flip the ratio to favour human cells over bacteria


However, the results, which concluded a rough re-estimate of the ratio to be more like 1 : 1.3 of human cells to bacteria, was actually highly variable – and perhaps no more accurate than Luckey’s original work.

As a bioinformatician from the European Molecular Biology Laboratory in Heidelberg (Germany), Peer Bork, explained that although progress in this respect is necessary, he doesn’t believe the results are anywhere near statistically significant – yet.

Evidently, a better method to quantify the Human Microbiome needs to be established before any reliable data can be extrapolated. And I can’t help but feels that settling on such fundamentals in Microbiomics should be of higher priority, particularly given how fast we are progressing in the therapeutic applications of manipulating our Microbiota.

Feature Image Credit: The GI Tract – © T. L. Furrer (BigStock ID56636615 )

UPDATE (26/01/16): Corrected typo on Human cell – Microbial ratio (from 1:3) to 1 : 1.3

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