Counting Cells

A person likely carries the same number of human and microbial cells, according to a new estimate.

By Jef Akst | January 11, 2016

Human blood prepared on a slideFLICKR, SMALLER.PATHOLOGICAL.CAMicrobiologist Thomas Luckey, who in 1972 estimated that the number of microbial cells in and on the human body outnumbers those carrying the human genome by 10 to 1, was wrong: people are not more microbe than human, scientists now suggest. According to new research from scientists in Israel and Canada, a 5”7’, 20-year-old man weighing 70 kilograms (154 pounds) likely harbors some 30 trillion human cells (the vast majority of which are red blood cells) and 39 trillion bacteria.

“The numbers are similar enough that each defecation event may flip the ratio to favour human cells over bacteria,” the researchers wrote in a paper posted to the preprint server bioRxiv last week (January 6).

“One-to-one is pretty impressive,” Judah Rosner, a molecular biologist at the National Institute of Diabetes and Digestive and Kidney Diseases who questioned the 10-to-1 ratio in a 2014 issue of Microbe, told Science News. “There’s as much of them as there is of us.” 

Of course, the new estimate could be off by as much as 25 percent, the researchers noted, as it’s based on existing experimental data that could inform an assessment of human and microbial cell counts, such as estimates of bacteria in 1 gram of feces and data on the length of the human colon. Moreover, the team only considered bacteria; virus, fungi, and other microbes could push that ratio up, geneticist Julie Segre of the National Human Genome Research Institute told Science News.

But the exact number may not matter, said Peer Bork, a bioinformatician at the European Molecular Biology Laboratory in Heidelberg, Germany. “It is good that we all now have a better estimate to quote,” he told Nature. “But I don’t think it will actually have any biological significance.”

Update (January 29): The researchers published their results in Cell this week (January 28). 

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Avatar of: James V. Kohl

James V. Kohl

Posts: 531

January 12, 2016

The biological significance of the links from the gut microbiome to the skin microbiome has gone missing. Some people might perceive the missing link to be a deliberate attempt to exclude nutrient energy-dependent metabolism and species-specific pheromones from consideration. 

Gut microbes link metabolic networks and genetic networks to the physiology of reproduction in all vertebrates and invertebrates. Typically the links include food odors and pheromones, but not necessarily when the skin microbiome is excluded.

I'm not demanding a recount, but a common sense approach to nutrient-dependent cell type differentiation and biodiversity should probably include the fact that Feedback loops link odor and pheromone signaling with reproduction.

If not, some of the ammunition is stolen from serious scientists who are Combating Evolution to Fight Disease. A better representation of biologically-based cause and effect is biologically significant to teleophiles -- if not to teleophobes.

See for instance: Effect of two pyrazine-containing chemosignals on cells of bone marrow and testes in male house mice (Mus musculus L.) The skin microbiome and gut microbiome are linked from the mouse model to humans via RNA-mediated events and amino acid substitutions.


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